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      Media Gateway Control (megaco)                C. Groves, M. Pantaleo
      Internet Draft                                           LM Ericsson
      Document: draft-ietf-megaco-h248v2-04.txt                T. Anderson
      Expires: October 2003                            Lucent Technologies
                                                                 T. Taylor
                                                           Nortel Networks
                                                                 (Editors)
                                                                April 2003
   
   
              The Megaco/H.248 Gateway Control Protocol, version 2
   
   Status of this Memo
   
      This document is an Internet-Draft and is in full conformance with
      all provisions of Section 10 of RFC2026.
   
      Internet-Drafts are working documents of the Internet Engineering
      Task Force (IETF), its areas, and its working groups.  Note that
      other groups may also distribute working documents as Internet-
      Drafts.
   
      Internet-Drafts are draft documents valid for a maximum of six months
      and may be updated, replaced, or obsoleted by other documents at any
      time.  It is inappropriate to use Internet-Drafts as reference
      material or to cite them other than as "work in progress."
   
      The list of current Internet-Drafts can be accessed at
           http://www.ietf.org/ietf/1id-abstracts.txt
      The list of Internet-Draft Shadow Directories can be accessed at
           http://www.ietf.org/shadow.html.
   
   Abstract
   
      This document describes the second version of the general-purpose
      gateway control protocol standardized as Megaco in the IETF and as
      Recommendation H.248 (now H.248.1) in the ITU-T.  It is common text
      with Recommendation H.248.1 (05/02), published by the ITU-T.  Megaco
      v2 includes the corrections to RFC 3015 which resulted in RFC xxxx
      [draft-ietf-megaco-3015corr-02.txt], plus the following new
      capabilities:
   
      - ability to audit specific properties, events, signals and
        statistics
      - use of serviceChange to indicate that capabilities have changed in
        the Media Gateway
      - playing a signal on the Root Termination
      - limiting the number of repetitions of transaction pending
      - allowing topology to be set per stream
      - ability to audit context properties
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      - new Nx64K multiplex type
      - provision for digit buffering when a digit map completes.
   
      In addition, the use of the Modem Descriptor was deprecated.
   
      A detailed list of changes from draft-ietf-megaco-3015corr-
      02.txt/H.248.1 (03/02) to this document is given in Appendix II at
      the end of this document.
   
   Conventions used in this document
   
      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
      "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
      document are to be interpreted as described in RFC-2119.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
   Table of Contents
   
      1           SCOPE.................................................6
   
      2           REFERENCES............................................6
      2.1         Normative references..................................7
      2.2         Informative references................................9
   
      3           DEFINITIONS..........................................10
   
      4           ABBREVIATIONS........................................11
   
      5           A NOTE ON CONVENTIONS................................12
   
      6           CONNECTION MODEL.....................................12
      6.1         Contexts.............................................15
      6.1.1       Context attributes and descriptors...................16
      6.1.2       Creating, deleting and modifying Contexts............16
      6.2         Terminations.........................................16
      6.2.1       Termination dynamics.................................20
      6.2.2       TerminationIDs.......................................20
      6.2.3       Packages.............................................21
      6.2.4       Termination properties and descriptors...............22
      6.2.5       Root Termination.....................................24
   
      7           COMMANDS.............................................25
      7.1         Descriptors..........................................26
      7.1.1       Specifying parameters................................26
      7.1.2       Modem descriptor.....................................27
      7.1.3       Multiplex descriptor.................................27
      7.1.4       Media descriptor.....................................28
      7.1.5       TerminationState descriptor..........................28
      7.1.6       Stream descriptor....................................29
      7.1.7       LocalControl descriptor..............................30
      7.1.8       Local and Remote descriptors.........................31
      7.1.9       Events descriptor....................................34
      7.1.10      EventBuffer descriptor...............................37
      7.1.11      Signals descriptor...................................37
      7.1.12      Audit descriptor.....................................39
      7.1.13      ServiceChange descriptor.............................40
      7.1.14      DigitMap descriptor..................................40
      7.1.14.1    DigitMap definition, creation, modification and
                      deletion.........................................40
      7.1.14.2    DigitMap Timers......................................41
      7.1.14.3    DigitMap Syntax......................................41
      7.1.14.4    DigitMap Completion Event............................42
      7.1.14.5    DigitMap Procedures..................................43
      7.1.14.6    DigitMap Activation..................................45
      7.1.14.7    Interaction Of DigitMap and Event Processing.........45
   
   
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      7.1.14.8    Wildcards............................................46
      7.1.14.9    Example..............................................46
      7.1.15      Statistics descriptor................................47
      7.1.16      Packages descriptor..................................47
      7.1.17      ObservedEvents descriptor............................47
      7.1.18      Topology descriptor..................................47
      7.1.19      Error Descriptor.....................................51
   
      7.2         Command Application Programming Interface............51
      7.2.1       Add..................................................52
      7.2.2       Modify...............................................53
      7.2.3       Subtract.............................................54
      7.2.4       Move.................................................56
      7.2.5       AuditValue...........................................57
      7.2.6       AuditCapabilities....................................60
      7.2.7       Notify...............................................62
      7.2.8       ServiceChange........................................63
      7.2.9       Manipulating and Auditing Context Attributes.........68
      7.2.10      Generic Command Syntax...............................69
   
      8           TRANSACTIONS.........................................69
      8.1         Common parameters....................................71
      8.1.1       Transaction Identifiers..............................71
      8.1.2       Context Identifiers..................................71
      8.2         Transaction Application Programming Interface........71
      8.2.1       TransactionRequest...................................72
      8.2.2       TransactionReply.....................................72
      8.2.3       TransactionPending...................................74
      8.3         Messages.............................................75
   
      9           TRANSPORT............................................75
      9.1         Ordering of Commands.................................76
      9.2         Protection against Restart Avalanche.................77
   
      10          SECURITY CONSIDERATIONS..............................78
      10.1        Protection of Protocol Connections...................79
      10.2        Interim AH scheme....................................79
      10.3        Protection of Media Connections......................80
   
      11          MG-MGC CONTROL INTERFACE.............................81
      11.1        Multiple Virtual MGs.................................81
      11.2        Cold start...........................................82
      11.3        Negotiation of protocol version......................82
      11.4        Failure of a MG......................................83
      11.5        Failure of an MGC....................................84
   
      12          PACKAGE DEFINITION...................................85
      12.1        Guidelines for defining packages.....................85
      12.1.1      Package..............................................86
   
   
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      12.1.2      Properties...........................................87
      12.1.3      Events...............................................88
      12.1.4      Signals..............................................88
      12.1.5      Statistics...........................................89
      12.1.6      Procedures...........................................89
      12.2        Guidelines to defining Parameters to Events and
                      Signals..........................................89
      12.3        Lists................................................90
      12.4        Identifiers..........................................90
      12.5        Package registration.................................91
   
      13          PROFILE DEFINITION...................................91
   
      14          IANA CONSIDERATIONS..................................92
      14.1        Packages.............................................92
      14.2        Error codes..........................................93
      14.3        ServiceChange reasons................................93
      14.4        Profiles.............................................94
   
      ANNEX A     BINARY ENCODING OF THE PROTOCOL......................95
      A.1         Coding of wildcards..................................95
      A.2         ASN.1 syntax specification...........................96
   
      ANNEX B     TEXT ENCODING OF THE PROTOCOL.......................120
      B.1         Coding of wildcards.................................120
      B.2         ABNF specification..................................120
      B.4         Hexadecimal octet sequence..........................137
   
      ANNEX C     TAGS FOR MEDIA STREAM PROPERTIES....................138
      C.1         General media attributes............................138
      C.2         Mux properties......................................140
      C.3         General bearer properties...........................140
      C.4         General ATM properties..............................141
      C.5         Frame Relay.........................................145
      C.6         IP 146
      C.7         ATM AAL2............................................146
      C.8         ATM AAL1............................................148
      C.9         Bearer capabilities.................................150
      C.10        AAL5 properties.....................................161
      C.11        SDP equivalents.....................................162
      C.12        H.245...............................................164
   
      ANNEX D     TRANSPORT OVER IP...................................165
      D.1         Transport over IP/UDP using Application Level Framing
                     (ALF)............................................165
      D.1.1       Providing At-Most-Once functionality................165
      D.1.2       Transaction identifiers and three-way handshake.....166
      D.1.2.1     Transaction identifiers.............................166
      D.1.2.2     Three-way handshake.................................166
   
   
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      D.1.3       Computing retransmission timers.....................167
      D.1.4       Provisional responses...............................168
      D.1.5       Repeating Requests, Responses and Acknowledgements..168
      D.2         Using TCP...........................................170
      D.2.1       Providing the At-Most-Once functionality............170
      D.2.2       Transaction identifiers and three-way handshake.....170
      D.2.3       Computing retransmission timers.....................170
      D.2.4       Provisional responses...............................171
      D.2.5       Ordering of commands................................171
   
      ANNEX E     BASIC PACKAGES......................................172
      E.1         Generic.............................................172
      E.2         Base Root Package...................................174
      E.3         Tone Generator Package..............................178
      E.4         Tone Detection Package..............................179
      E.5         Basic DTMF Generator Package........................182
      E.6         DTMF detection Package..............................184
      E.7         Call Progress Tones Generator Package...............186
      E.8         Call Progress Tones Detection Package...............187
      E.9         Analog Line Supervision Package.....................188
      E.10        Basic Continuity Package............................192
      E.11        Network Package.....................................195
      E.12        RTP Package.........................................197
      E.13        TDM Circuit Package.................................199
   
      APPENDIX I  Example Call Flows..................................201
      I.1         Residential Gateway to Residential Gateway Call.....201
      I.1.1       Programming Residential GW Analog Line Terminations
                      for Idle Behaviour..............................201
      I.1.2       Collecting Originator Digits and Initiating Termination
                     .................................................203
   
      APPENDIX II CHANGES FROM RFC XXXX [draft-ietf-megaco-3015corr
                     -02.txt].........................................213
   
      INTELLECTUAL PROPERTY RIGHTS....................................217
      Acknowledgments.................................................218
      Authors' Addresses..............................................219
   
   
   
   
   
   
   
   
   
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
   1  SCOPE
   
      This document defines the protocols used between elements of a
      physically decomposed multimedia gateway. There are no functional
      differences from a system view between a decomposed gateway, with
      distributed sub-components potentially on more than one physical
      device, and a monolithic gateway such as described in Recommendation
      H.246. This document does not define how gateways, multipoint control
      units or interactive voice response units (IVRs) work. Instead it
      creates a general framework that is suitable for these applications.
   
      Packet network interfaces may include IP, ATM or possibly others. The
      interfaces will support a variety of Switched Circuit Network (SCN)
      signalling systems, including tone signalling, ISDN, ISUP, QSIG and
      GSM. National variants of these signalling systems will be supported
      where applicable.
   
      Products claiming compliance with Version 1 of H.248.1 shall comply
      with all of the mandatory requirements of H.248.1 originally approved
      in 06/2000 and reissued in 03/2002.  H.248.1 (03/2002) is common text
      with RFC xxxx [draft-ietf-megaco-3015corr-03.txt].
   
      Products claiming compliance with Version 2 of H.248.1 shall comply
      with all of the mandatory requirements of H.248.1 approved on
      05/2002.  H.248.1 (05/2002) is common text with this document.
   
      Products shall indicate the version of the protocol in use by using
      ServiceChangeVersion as æ1Æ to refer to RFC xxxx/H.248.1 (03/2002)
      and æ2Æ to refer to this specification/H.248.1 (05/2002).
   
   
   2  REFERENCES
   
      The following ITU-T Recommendations and other references contain
      provisions which, through reference in this text, constitute
      provisions of this Recommendation. At the time of publication, the
      editions indicated were valid. All Recommendations and other
      references are subject to revision; all users of this Recommendation
      are therefore encouraged to investigate the possibility of applying
      the most recent edition of the Recommendations and other references
      listed below. A list of the currently valid ITU-T Recommendations is
      regularly published.
   
   2.1   Normative references
   
      -  ITU-T Recommendation H.225.0 (2000), Call signalling protocols and
         media stream packetization for packet-based multimedia
         communication systems.
   
   
   
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      -  ITU-T Recommendation H.235 (1998), Security and encryption for H-
         Series (H.323 and other H.245-based) multimedia terminals.
   
      -  ITU-T Recommendation H.245 (1998), Control protocol for multimedia
         communication.
   
      -  ITU-T Recommendation H.246 (1998), Interworking of H-series
         multimedia terminals with H-series multimedia terminals and
         voice/voiceband terminals on GSTN and ISDN.
   
      -  ITU-T Recommendation H.248.4 (2000), Transport over Stream Control
         Transmission Protocol (SCTP).
   
      -  ITU-T Recommendation H.248.5 (2000), Transport over ATM.
   
      -  ITU-T Recommendation H.248.8 (2002), H.248 Error Codes and Service
         Change Reasons.
   
      -  ITU-T Recommendation H.323 (1999), Packet-based multimedia
         communication systems.
   
      -  ITU-T Recommendation I.363.1 (1996), B-ISDN ATM adaptation layer
         (AAL) specification: Type 1 AAL.
   
      -  ITU-T Recommendation I.363.2 (1997), B-ISDN ATM adaptation layer
         (AAL) specification: Type 2 AAL.
   
      -  ITU-T Recommendation I.363.5 (1996), B-ISDN ATM adaptation layer
         (AAL) specification: Type 5 AAL.
   
      -  ITU-T Recommendation I.366.1 (1998), Segmentation and Reassembly
         Service Specific Convergence Sublayer for the AAL type 2.
   
      -  ITU-T Recommendation I.366.2 (1999), AAL type 2 service specific
         convergence sublayer for trunking.
   
      -  ITU-T Recommendation I.371 (2000), Traffic control and congestion
         control in B-ISDN.
   
      -  ITU-T Recommendation Q.763 (1999), Signalling System No. 7 - ISDN
         user part formats and codes.
   
      -  ITU-T Recommendation Q.765.5 (2001), Application transport
         mechanism - Bearer independent call control (BICC).
   
      -  ITU-T Recommendation Q.931 (1998), ISDN user-network interface
         layer 3 specification for basic call control.
   
   
   
   
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      -  ITU-T Recommendation Q.2630.1 (1999), AAL type 2 signalling
         protocol (Capability Set 1).
   
      -  ITU-T Recommendation Q.2931 (1995), Digital Subscriber Signalling
         System No. 2 (DSS2) - User-Network Interface (UNI)  Layer 3
         specification for basic call/connection control.
   
      -  ITU-T Recommendation Q.2941.1 (1997), Digital Subscriber
         Signalling System No. 2 - Generic identifier transport.
   
      -  ITU-T Recommendation Q.2961.1 (1995), Additional signalling
         capabilities to support traffic parameters for the tagging option
         and the sustainable call note parameter set.
   
      -  ITU-T Recommendation Q.2961.2 (1997), Additional traffic
         parameters: Support of ATM transfer capability in the broadband
         bearer capability information element.
   
      -  ITU-T Recommendation Q.2965.1 (1999), Digital subscriber
         signalling system No. 2 - Support of Quality of Service classes.
   
      -  ITU-T Recommendation Q.2965.2 (1999), Digital subscriber
         signalling system No. 2 - Signalling of individual Quality of
         Service parameters.
   
      -  ITU-T Recommendation V.76 (1996), Generic multiplexer using V.42
         LAPM-based procedures.
   
      -  ITU-T Recommendation X.213 (1995), Information technology - Open
         Systems Interconnection - Network service definition plus
         Amendment 1 (1997), Addition of the Internet protocol address
         format identifier.
   
      -  ITU-T Recommendation X.680 (1997), Information technology -
         Abstract Syntax Notation One (ASN.1): Specification of basic
         notation.
   
      -  ITU-T Recommendation X.690 (1997), Information Technology - ASN.1
         Encoding Rules: Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished Encoding Rules
         (DER).
   
      -  ATM Forum (1996), ATM User-Network Interface (UNI) Signalling
         Specification - Version 4.0.
   
      -  RFC 1006, ISO Transport Service on top of the TCP, Version 3.
   
      -  RFC 2026, The Internet Standards Process -- Revision 3.
   
   
   
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      -  RFC 2119, Key words for use in RFCs to Indicate Requirement
         Levels.
   
      -  RFC 2234, Augmented BNF for Syntax Specifications: ABNF.
   
      -  RFC 2327, SDP: Session Description Protocol.
   
      -  RFC 2402, IP Authentication Header.
   
      -  RFC 2406, IP Encapsulating Security Payload (ESP).
   
   2.2   Informative references
   
      -  ITU-T Recommendation E.180/Q.35 (1998), Technical characteristics
         of tones for the telephone service.
   
      -  ITU-T Recommendation G.711 (1988), Pulse Code Modulation (PCM) of
         voice frequencies.
   
      -  ITU-T Recommendation H.221 (1999), Frame structure for a 64 to
         1920 kbit/s channel in audiovisual teleservices.
   
      -  ITU-T Recommendation H.223 (1996), Multiplexing protocol for low
         bit rate multimedia communication.
   
      -  ITU-T Recommendation H.226 (1998), Channel aggregation protocol
         for multilink operation on circuit-switched networks.
   
      -  ITU-T Recommendation Q.724 (1998), Signalling procedures.
   
      -  ITU-T Recommendation Q.764 (1999), Signalling system No. 7 - ISDN
         user part signalling procedures.
   
      -  ITU-T Recommendation Q.1902.4 (2001), Bearer independent call
         control protocol - Basic call procedures.
   
      -  RFC 768, User Datagram Protocol.
   
      -  RFC 791, Internet protocol.
   
      -  RFC 793, Transmission control protocol.
   
      -  RFC 1661, The Point-to-Point Protocol (PPP).
   
      -  RFC 1889, RTP: A Transport Protocol for Real-Time Applications.
   
      -  RFC 1890, RTP Profile for Audio and Video Conferences with Minimal
         Control.
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      -  RFC 2401, Security Architecture for the Internet Protocol.
   
      -  RFC 2543, SIP: Session Initiation Protocol.
   
      -  RFC 2460, Internet Protocol, Version 6 (IPv6) Specification.
   
      -  RFC 2805, Media Gateway Control Protocol Architecture and
         Requirements.
   
   
   3  DEFINITIONS
   
      This document defines the following terms:
   
      Access gateway:
      A type of gateway that provides a User-Network Interface (UNI) such
      as ISDN.
   
      Descriptor:
      A syntactic element of the protocol that groups related properties.
      For instance, the properties of a media flow on the MG can be set by
      the MGC by including the appropriate descriptor in a command.
   
      Media Gateway (MG):
      The media gateway converts media provided in one type of network to
      the format required in another type of network. For example, a MG
      could terminate bearer channels from a switched circuit network (e.g.
      DS0s) and media streams from a packet network (e.g. RTP streams in an
      IP network). This gateway may be capable of processing audio, video
      and T.120 alone or in any combination, and will be capable of full
      duplex media translations. The MG may also play audio/video messages
      and perform other IVR functions, or may perform media conferencing.
   
      Media Gateway Controller (MGC):
      Controls the parts of the call state that pertain to connection
      control for media channels in a MG.
   
      Multipoint Control Unit (MCU):
      An entity that controls the setup and coordination of a multi-user
      conference that typically includes processing of audio, video and
      data.
   
      Residential gateway:
      A gateway that interworks an analogue line to a packet network. A
      residential gateway typically contains one or two analogue lines and
      is located at the customer premises.
   
   
   
   
   
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      SCN FAS signalling gateway:
      This function contains the SCN Signalling Interface that terminates
      SS7, ISDN or other signalling links where the call control channel
      and bearer channels are collocated in the same physical span.
   
      SCN NFAS signalling gateway:
      This function contains the SCN Signalling Interface that terminates
      SS7 or other signalling links where the call control channels are
      separated from bearer channels.
   
      Stream:
      Bidirectional media or control flow received/sent by a media gateway
      as part of a call or conference.
   
      Trunk:
      A communication channel between two switching systems such as a DS0
      on a T1 or E1 line.
   
      Trunking gateway:
      A gateway between SCN network and packet network that typically
      terminates a large number of digital circuits.
   
   
   4  ABBREVIATIONS
   
      This document uses the following abbreviations:
   
      ALF   Application Layer Framing
   
      ATM   Asynchronous Transfer Mode
   
      CAS   Channel Associated Signalling
   
      DTMF  Dual Tone Multi-Frequency
   
      FAS   Facility Associated Signalling
   
      GSM   Global System for Mobile communications
   
      GW    GateWay
   
      IANA  Internet Assigned Numbers Authority (superseded by Internet
            Corporation for Assigned Names and Numbers (ICANN))
   
      IP    Internet Protocol
   
      ISUP  ISDN User Part
   
      IVR   Interactive Voice Response
   
   
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      MG    Media Gateway
   
      MGC   Media Gateway Controller
   
      NFAS  Non-Facility Associated Signalling
   
      PRI   Primary Rate Interface
   
      PSTN  Public Switched Telephone Network
   
      QoS   Quality of Service
   
      RTP   Real-time Transport Protocol
   
      SCN   Switched Circuit Network
   
      SG    Signalling Gateway
   
      SS7   Signalling System No. 7
   
   
   5  A NOTE ON CONVENTIONS
   
      According to ITU-T practice, "SHOULD" refers to a suggested but
      optional feature or procedure.  "SHOULD" as used by the ITU-T is thus
      a weaker requirement level than in IETF practice as defined in RFC
      2119 and cited at the beginning of this document.  In view of this
      difference, the present document calls out all instances of "SHOULD"
      for review and replacement by "suggested" where that appears to be
      the intent.
   
   6  CONNECTION MODEL
   
      The connection model for the protocol describes the logical entities,
      or objects, within the Media Gateway that can be controlled by the
      Media Gateway Controller. The main abstractions used in the
      connection model are Terminations and Contexts.
   
      A Termination sources and/or sinks one or more streams. In a
      multimedia conference, a Termination can be multimedia and sources or
      sinks multiple media streams. The media stream parameters, as well as
      bearer parameters are encapsulated within the Termination.
   
      A Context is an association between a collection of Terminations.
      There is a special type of Context, the null Context, which contains
      all Terminations that are not associated to any other Termination.
      For instance, in a decomposed access gateway, all idle lines are
      represented by Terminations in the null Context.
   
   
   
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      Following is a graphical depiction of these concepts. The diagram of
      Figure 1 gives several examples and is not meant to be an all-
      inclusive illustration. The asterisk box in each of the Contexts
      represents the logical association of Terminations implied by the
      Context.
   
            +------------------------------------------------------+
            |Media Gateway                                         |
            | +-------------------------------------------------+  |
            | |Context                          +-------------+ |  |
            | |                                 | Termination | |  |
            | |                                 |-------------| |  |
            | |  +-------------+             +->| SCN Bearer  |<---+->
            | |  | Termination |   +-----+   |  |   Channel   | |  |
            | |  |-------------|   |     |---+  +-------------+ |  |
          <-+--->| RTP Stream  |---|  *  |                      |  |
            | |  |             |   |     |---+  +-------------+ |  |
            | |  +-------------+   +-----+   |  | Termination | |  |
            | |                              |  |-------------| |  |
            | |                              +->| SCN Bearer  |<---+->
            | |                                 |   Channel   | |  |
            | |                                 +-------------+ |  |
            | +-------------------------------------------------+  |
            |                                                      |
            |                                                      |
            |                    +------------------------------+  |
            |   (NULL Context)   |Context                       |  |
            |  +-------------+   |              +-------------+ |  |
            |  | Termination |   | +-----+      | Termination | |  |
            |  |-------------|   | |     |      |-------------| |  |
            |  | SCN Bearer  |   | |  *  |------| SCN Bearer  |<---+->
            |  |   Channel   |   | |     |      |   Channel   | |  |
            |  +-------------+   | +-----+      +-------------+ |  |
            |                    +------------------------------+  |
            |                                                      |
            |                                                      |
            | +-------------------------------------------------+  |
            | |Context                                          |  |
            | |  +-------------+                +-------------+ |  |
            | |  | Termination |   +-----+      | Termination | |  |
            | |  |-------------|   |     |      |-------------| |  |
          <-+--->| SCN Bearer  |---|  *  |------| SCN Bearer  |<---+->
            | |  |   Channel   |   |     |      |   Channel   | |  |
            | |  +-------------+   +-----+      +-------------+ |  |
            | +-------------------------------------------------+  |
            | ___________________________________________________  |
            +------------------------------------------------------+
   
               Figure 1: Examples of Megaco/H.248 Connection Model
   
   
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      The example in Figure 2 shows an example of one way to accomplish a
      call-waiting scenario in a decomposed access gateway, illustrating
      the relocation of a Termination between Contexts. Terminations T1 and
      T2 belong to Context C1 in a two-way audio call. A second audio call
      is waiting for T1 from Termination T3. T3 is alone in Context C2. T1
      accepts the call from T3, placing T2 on hold. This action results in
      T1 moving into Context C2, as shown in Figure 3.
   
            +------------------------------------------------------+
            |Media Gateway                                         |
            | +-------------------------------------------------+  |
            | |Context C1                                       |  |
            | |  +-------------+                +-------------+ |  |
            | |  | Term. T2    |   +-----+      | Term. T1    | |  |
            | |  |-------------|   |     |      |-------------| |  |
          <-+--->| RTP Stream  |---|  *  |------| SCN Bearer  |<---+->
            | |  |             |   |     |      |   Channel   | |  |
            | |  +-------------+   +-----+      +-------------+ |  |
            | +-------------------------------------------------+  |
            |                                                      |
            | +-------------------------------------------------+  |
            | |Context C2                                       |  |
            | |                                 +-------------+ |  |
            | |                    +-----+      | Term. T3    | |  |
            | |                    |     |      |-------------| |  |
            | |                    |  *  |------| SCN Bearer  |<---+->
            | |                    |     |      |   Channel   | |  |
            | |                    +-----+      +-------------+ |  |
            | +-------------------------------------------------+  |
            +------------------------------------------------------+
   
        Figure 2: Example Call Waiting Scenario / Alerting Applied to T1
   
   
            +------------------------------------------------------+
            |Media Gateway                                         |
            | +-------------------------------------------------+  |
            | |Context C1                                       |  |
            | |  +-------------+                                |  |
            | |  | Term. T2    |   +-----+                      |  |
            | |  |-------------|   |     |                      |  |
          <-+--->| RTP Stream  |---|  *  |                      |  |
            | |  |             |   |     |                      |  |
            | |  +-------------+   +-----+                      |  |
            | +-------------------------------------------------+  |
            |                                                      |
            | +-------------------------------------------------+  |
   
   
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            | |Context C2                                       |  |
            | |  +-------------+                +-------------+ |  |
            | |  | Term. T1    |   +-----+      | Term. T3    | |  |
            | |  |-------------|   |     |      |-------------| |  |
          <-+--->| SCN Bearer  |---|  *  |------| SCN Bearer  |<---+->
            | |  |   Channel   |   |     |      |   Channel   | |  |
            | |  +-------------+   +-----+      +-------------+ |  |
            | +-------------------------------------------------+  |
            +------------------------------------------------------+
   
             Figure 3. Example Call Waiting Scenario / Answer by T1
   
   
   
   6.1   Contexts
   
      A Context is an association between a number of Terminations. The
      Context describes the topology (who hears/sees whom) and the media
      mixing and/or switching parameters if more than two Terminations are
      involved in the association.
   
      There is a special Context called the null Context. It contains
      Terminations that are not associated to any other Termination.
      Terminations in the null Context can have their parameters examined
      or modified, and may have events detected on them.
   
      In general, an Add command is used to add Terminations to Contexts.
      If the MGC does not specify an existing Context to which the
      Termination is to be added, the MG creates a new Context. A
      Termination may be removed from a Context with a Subtract command,
      and a Termination may be moved from one Context to another with a
      Move command. A Termination SHALL exist in only one Context at a
      time.
   
      The maximum number of Terminations in a Context is a MG property.
      Media gateways that offer only point-to-point connectivity might
      allow at most two Terminations per Context. Media gateways that
      support multipoint conferences might allow three or more Terminations
      per Context.
   
   6.1.1 Context attributes and descriptors
   
      The attributes of Contexts are:
   
      -  ContextID.
   
      -  The topology (who hears/sees whom).
   
   
   
   
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         The topology of a Context describes the flow of media between the
         Terminations within a Context. In contrast, the mode of a
         Termination (send/receive/...) describes the flow of the media at
         the ingress/egress of the media gateway.
   
      -  The priority is used for a Context in order to provide the MG with
         information about a certain precedence handling for a Context. The
         MGC can also use the priority to control autonomously the traffic
         precedence in the MG in a smooth way in certain situations (e.g.
         restart), when a lot of Contexts must be handled simultaneously.
         Priority 0 is the lowest priority and a priority of 15 is the
         highest priority.
   
      -  An indicator for an emergency call is also provided to allow a
         preference handling in the MG.
   
   6.1.2 Creating, deleting and modifying Contexts
   
      The protocol can be used to (implicitly) create Contexts and modify
      the parameter values of existing Contexts. The protocol has commands
      to add Terminations to Contexts, subtract them from Contexts, and to
      move Terminations between Contexts. Contexts are deleted implicitly
      when the last remaining Termination is subtracted or moved out.
   
   6.2   Terminations
   
      A Termination is a logical entity on a MG that sources and/or sinks
      media and/or control streams. A Termination is described by a number
      of characterizing Properties, which are grouped in a set of
      Descriptors that are included in commands. Terminations have unique
      identities (TerminationIDs), assigned by the MG at the time of their
      creation.
   
      Terminations representing physical entities have a semi-permanent
      existence. For example, a Termination representing a TDM channel
      might exist for as long as it is provisioned in the gateway.
      Terminations representing ephemeral information flows, such as RTP
      flows, would usually exist only for the duration of their use.
   
      Ephemeral Terminations are created by means of an Add command. They
      are destroyed by means of a Subtract command. In contrast, when a
      physical Termination is Added to or Subtracted from a Context, it is
      taken from or to the null Context, respectively.
   
      Terminations may have signals applied to them (see 7.1.11).
      Terminations may be programmed to detect Events, the occurrence of
      which can trigger notification messages to the MGC, or action by the
      MG. Statistics may be accumulated on a Termination. Statistics are
   
   
   
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      reported to the MGC upon request (by means of the AuditValue command,
      see 7.2.5) and when the Termination is subtracted from a context.
   
      Multimedia gateways may process multiplexed media streams. For
      example, Recommendation H.221 describes a frame structure for
      multiple media streams multiplexed on a number of digital 64 kbit/s
      channels. Such a case is handled in the connection model in the
      following way. For every bearer channel that carries part of the
      multiplexed streams, there is a physical or ephemeral "bearer
      Termination". The bearer Terminations that source/sink the digital
      channels are connected to a separate Termination called the
      "multiplexing Termination". The multiplexing termination is an
      ephemeral termination representing a frame-oriented session. The
      MultiplexDescriptor for this Termination describes the multiplex used
      (e.g. H.221 for an H.320 session) and indicates the order in which
      the contained digital channels are assembled into a frame.
   
      Multiplexing terminations may be cascades (e.g., H.226 multiplex of
      digital channels feeding into a H.223 multiplex supporting an H.324
      session).
   
      The individual media streams carried in the session are described by
      StreamDescriptors on the multiplexing Termination. These media
      streams can be associated with streams sourced/sunk by Terminations
      in the Context other than the bearer Terminations supporting the
      multiplexing Termination.  Each bearer Termination supports only a
      single data stream.  These data streams do not appear explicitly as
      streams on the multiplexing Termination and they are hidden from the
      rest of the context.
   
      Figures 4, 5, 6, and 6a illustrate typical applications of the
      multiplexing termination and Multiplex Descriptor.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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                     +-----------------------------------+
                     | Context     +-------+             |
                    +----+         |       |             |
      Circuit 1 -|--| TC1|---------+ Tmux  |             |
                 |  +----+ (Str 1) |       |  Audio    +-----+
                 |   |             |       +-----*-----+     |-----
                 |  +----+         | H.22x | Stream 1  |     |
      Circuit 2 -|--| TC2|---------+ multi-|           | TR1 |
                 |  +----+ (Str 1) | plex  |           |(RTP)|
                 |   |             |       |  Video    |     |
                 |  +----+         |       +-----*-----+     |-----
      Circuit 3 -|--| TC3|---------+       | Stream 2  |     |
                 /  +----+ (Str 1) |       |           +-----+
                /    |             +-------+             |
               /     +-----------------\-----------------+
      Audio, video, and control         \
      signals are carried in frames    Tmux is an ephemeral with two
      spanning the circuits.           explicit Stream Descriptors
                                       and a Multiplex Descriptor.
   
         Figure 4: Multiplexed Termination Scenario - Circuit to Packet
                 (Asterisks * denote the centre of the context)
   
   
   
                       Context
                     +--------------------------------------+
                     |       +-------+        +-------+     |
                    +----+   |       |        |       |   +----+
      Circuit 1 ----| TC1|---+ Tmux1 |  Audio | Tmux2 +---| TC4|---
                    +----+   |       +---*----+       |   +----+
                     |       |       |  Str 1 |       |     |
                    +----+   | H.22x |        | H.22x |   +----+
      Circuit 2 ----| TC2|---+ multi-|        | multi-+---| TC5|---
                    +----+   | plex  |        | plex  |   +----+
                     |       |       |  Video |       |     |
                    +----+   |       +---*----+       |   +----+
      Circuit 3 ----| TC3|---+       |  Str 2 |       +---| TC6|---
                    +----+   |       |        |       |   +----+
                     |       +-------+        +-------+     |
                     +-----------------\-----/--------------+
                                        \   /
                Tmux1 and Tmux2 are ephemerals each with two
      .         explicit Stream Descriptors and a Multiplex Descriptor.
   
         Figure 5: Multiplexed Termination Scenario - Circuit to Circuit
                 (Asterisks * denote the centre of the context)
   
   
   
   
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                     +-----------------------------------+
                     | Context     +-------+             |
                    +----+         |       |             |
      Circuit 1 -|--| TC1|---------+ Tmux  |             |
                 |  +----+ (Str 1) |       |  Audio    +-----+
                 |   |             |       +-----*-----+ TR1 |-----
                 |  +----+         | H.22x | Stream 1  |(RTP)|
      Circuit 2 -|--| TC2|---------+ multi-|           +-----+
                 |  +----+ (Str 1) | plex  |             |
                 |   |             |       |  Video    +-----+
                 |  +----+         |       +-----*-----+ TR2 |-----
      Circuit 3 -|--| TC3|---------+       | Stream 2  |(RTP)|
                 /  +----+ (Str 1) |       |           +-----+
                /    |             +-------+             |
               /     +-----------------\-----------------+
      Audio, video, and control         \
      signals are carried in frames    Tmux is an ephemeral with two
      spanning the circuits.           explicit Stream Descriptors
                                       and a Multiplex Descriptor.
   
         Figure 6: Multiplexed Termination Scenario - Single to Multiple
                                  Terminations
                 (Asterisks * denote the centre of the context)
   
   
   
   
               Context
             +---------------------------------------------+
             |       +-------+       +-------+             |
      Cct 1 +----+   |       |       |       | Audio     +-----+
        ----| TC1|---+ Tmux1 |       | Tmux2 +-----*-----| TR1 |-----
            +----+   |       |       |       | Stream 1  |(RTP)|
             |       |       | Data  |       |           +-----+
      Cct 2 +----+   | H.226 +-------+ H.223 |             |
        ----| TC2|---+ multi-|(Str 1)| multi-| Control   +-----+
            +----+   | plex  |       | plex  +-----*-----+ Tctl|-----
             |       |       |       |       | Stream 3  +-----+
      Cct 3 +----+   |       |       |       |             |
        ----| TC3|---+       |       |       |           +-----+
            +----+   |       |       |       +-----*-----+ TR2 |-----
             |       +-------+       |       |  Video    |(RTP)|
             |                       +-------+ Stream 2  +-----+
             |                                             |
             +---------------------------------------------+
           Tmux1 has a Multiplex Descriptor and a single data stream.
           Tmux2 has a Multiplex Descriptor with a single bearer and
           three explicit Stream Descriptors.
   
   
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       Figure 6a: Multiplexed Termination Scenario - Cascaded Multiplexes
                 (Asterisks * denote the centre of the context)
               Note: this figure does not appear in Rec. H.248.1.
   
      ----
   
      Unlike the multiplexing terminations described in the previous
      paragraphs, multiplexed bearer terminations, which represent
      multiplexed bearers such as ATM AAL Type 2 bearers, carry no media
      streams.  They are present strictly for the purpose of modeling the
      creation and destruction of the actual bearer.  When a new
      multiplexed bearer is to be created, an ephemeral Termination is
      created in a Context established for this purpose.  When the
      Termination is subtracted, the multiplexed bearer is destroyed.
   
   6.2.1 Termination dynamics
   
      The protocol can be used to create new Terminations and to modify
      property values of existing Terminations. These modifications include
      the possibility of adding or removing events and/or signals. The
      Termination properties, and events and signals are described in the
      ensuing subclauses. An MGC can only release/modify Terminations and
      the resources that the Termination represents, which it has
      previously seized via e.g. the Add command.
   
   6.2.2 TerminationIDs
   
      Terminations are referenced by a TerminationID, which is an arbitrary
      schema chosen by the MG.
   
      TerminationIDs of physical Terminations are provisioned in the Media
      Gateway. The TerminationIDs may be chosen to have structure. For
      instance, a TerminationID may consist of trunk group and a trunk
      within the group.
   
      A wildcarding mechanism using two types of wildcards can be used with
      TerminationIDs. The two wildcards are ALL and CHOOSE. The former is
      used to address multiple Terminations at once, while the latter is
      used to indicate to a media gateway that it must select a Termination
      satisfying the partially specified TerminationID. This allows, for
      instance, that a MGC instructs a MG to choose a circuit within a
      trunk group.
   
      When ALL is used in the TerminationID of a command, the effect is
      identical to repeating the command with each of the matching
      TerminationIDs. The use of ALL does not address the ROOT termination.
      Since each of these commands may generate a response, the size of the
      entire response may be large. If individual responses are not
   
   
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      required, a wildcard response may be requested. In such a case, a
      single response is generated, which contains the UNION of all of the
      individual responses which otherwise would have been generated, with
      duplicate values suppressed. For instance, given a Termination Ta
      with properties p1=a, p2=b and Termination Tb with properties p2=c,
      p3=d, a UNION response would consist of a wildcarded TerminationId
      and the sequence of properties p1=a, p2=b,c and p3=d. Wildcard
      response may be particularly useful in the Audit commands.
   
      The encoding of the wildcarding mechanism is detailed in Annexes A
      and B.
   
   6.2.3 Packages
   
      Different types of gateways may implement Terminations that have
      widely differing characteristics. Variations in Terminations are
      accommodated in the protocol by allowing Terminations to have
      optional Properties, Events, Signals and Statistics implemented by
      MGs.
   
      In order to achieve MG/MGC interoperability, such options are grouped
      into Packages, and typically a Termination realizes a set of such
      Packages. More information on definition of packages can be found in
      clause 12. An MGC can audit a Termination to determine which Packages
      it realizes.
   
      Properties, Events, Signals and Statistics defined in Packages, as
      well as parameters to them, are referenced by identifiers (Ids).
      Identifiers are scoped. For each package, PropertyIds, EventIds,
      SignalIds, StatisticsIds and ParameterIds have unique name spaces and
      the same identifier may be used in each of them. Two PropertyIds in
      different packages may also have the same identifier, etc.
   
      To support a particular package the MG must support all properties,
      signals, events and statistics defined in a package. It must also
      support all Signal and Event parameters. The MG may support a subset
      of the values listed in a package for a particular Property or
      Parameter.
   
      When packages are extended, the properties, events, signals and
      statistics defined in the base package can be referred to using
      either the extended package name or the base package name.  For
      example, if Package A defines event e1, and Package B extends Package
      A, then B/e1 is an event for a termination implementing Package B. By
      definition, the MG MUST also implement the base Package, but it is
      optional to publish the base package as an allowed interface.  If it
      does publish  A, then A would be reported on the Package Descriptor
      in AuditValue as well as B, and event A/e1 would be available on a
      termination.  If the MG does not publish A, then only B/e1 would be
   
   
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      available.  If published through AuditValue, A/e1 and B/e1 are the
      same event.
   
      For improved interoperability and backward compatibility, an MG MAY
      publish all Packages supported by its Terminations, including base
      Packages from which extended Packages are derived.  An exception to
      this is in cases where the base packages are expressly "Designed to
      be extended only".
   
   6.2.4 Termination properties and descriptors
   
      Terminations have properties. The properties have unique PropertyIDs.
      Most properties have default values, which are explicitly defined in
      this protocol specification or in a package (see clause 12) or set by
      provisioning. If not provisioned otherwise, the properties in all
      descriptors except TerminationState and LocalControl default to
      empty/"no value" when a Termination is first created or returned to
      the null Context. The default contents of the two exceptions are
      described in 7.1.5 and 7.1.7.
   
      The provisioning of a property value in the MG will override any
      default value, be it supplied in this protocol specification or in a
      package.  Therefore if it is essential for the MGC to have full
      control over the property values of a Termination, it SHOULD supply
      explicit values when ADDing the Termination to a Context.
      Alternatively, for a physical Termination the MGC can determine any
      provisioned property values by auditing the Termination while it is
      in the NULL Context.
   
      There are a number of common properties for Terminations and
      properties specific to media streams. The common properties are also
      called the Termination state properties. For each media stream, there
      are local properties and properties of the received and transmitted
      flows.
   
      Properties not included in the base protocol are defined in Packages.
      These properties are referred to by a name consisting of the
      PackageName and a PropertyId. Most properties have default values
      described in the Package description. Properties may be read-only or
      read/write. The possible values of a property may be audited, as can
      their current values. For properties that are read/write, the MGC can
      set their values. A property may be declared as "Global" which has a
      single value shared by all Terminations realizing the package.
      Related properties are grouped into descriptors for convenience.
   
      When a Termination is added to a Context, the value of its read/write
      properties can be set by including the appropriate descriptors as
      parameters to the Add command. Similarly, a property of a Termination
      in a Context may have its value changed by the Modify command.
   
   
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      Properties may also have their values changed when a Termination is
      moved from one Context to another as a result of a Move command. In
      some cases, descriptors are returned as output from a command.
   
      In general, if a Descriptor is completely omitted from one of the
      aforementioned Commands, the properties in that Descriptor retain
      their prior values for the Termination(s) upon which the Command
      acts. On the other hand, if some read/write properties are omitted
      from a Descriptor in a Command (i.e., the Descriptor is only
      partially specified), those properties will be reset to their default
      values for the Termination(s) upon which the Command acts, unless the
      package specifies other behavior. For more details, see clause 7.1
      dealing with the individual Descriptors.
   
      The following table lists all of the possible descriptors and their
      use. Not all descriptors are legal as input or output parameters to
      every command.
   
      Descriptor name   Description
   
      Modem             Identifies modem type and properties when
                         applicable(*).
   
      Mux               Describes multiplex type for multimedia
                         Terminations (e.g. H.221, H.223, H.225.0) and
                         Terminations forming the input mux.
   
      Media             A list of media stream specifications (see
                         7.1.4).
   
      TerminationState  Properties of a Termination (which can be
                         defined in Packages) that are not stream
                         specific.
   
      Stream            A list of remote/local/localControl
                         descriptors for a single stream.
   
      Local             Contains properties that specify the media
                         flows that the MG receives from the remote
                         entity.
   
      Remote            Contains properties that specify the media
                         flows that the MG sends to the remote entity.
   
      LocalControl      Contains properties (which can be defined in
                         packages) that are of interest between the MG
                         and the MGC.
   
   
   
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      Descriptor name   Description
   
      Events            Describes events to be detected by the MG and
                         what to do when an event is detected.
   
      EventBuffer       Describes events to be detected by the MG when
                         Event Buffering is active.
   
      Signals           Describes signals (see 7.1.11) applied  to
                         Terminations.
   
      Audit             In Audit commands, identifies which
                         information is desired.
   
      Packages          In AuditValue, returns a list of Packages
                         realized by Termination.
   
      DigitMap          Defines patterns against which sequences of a
                         specified set of events  are to be matched so
                         they can be reported as a group rather than
                         singly.
   
      ServiceChange     In ServiceChange, what, why service change
                         occurred, etc.
   
      ObservedEvents    In Notify or AuditValue, report of events
                         observed.
   
      Statistics        In Subtract and Audit, report of Statistics
                         kept on a Termination.
   
      Topology          Specifies flow directions between Terminations
                         in a Context.
   
      Error             Contains an error code and optionally error
                         text; it may occur in command replies and in
                         Notify requests.
   
      (*) ModemDescriptor has been deprecated in Megaco v2/H.248.1
      (05/2002).
   
   
   
   6.2.5 Root Termination
   
      Occasionally, a command must refer to the gateway as an entity in
      itself, rather than a Termination within it. A special TerminationID,
      "Root" is reserved for this purpose. Packages may be defined on Root.
   
   
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      Root thus may have properties, events, signals and statistics.
      Accordingly, the root TerminationID may appear in:
   
      -  a Modify command - to change a property, send a signal or set an
         event
   
      -  a Notify command - to report an event
   
      -  an AuditValue return - to examine the values of properties and
         statistics implemented on root
   
      -  an AuditCapability - to determine what properties of root are
         implemented
   
      -  a ServiceChange - to declare the gateway in or out of service.
   
      Any other use of the root TerminationID is an error. Error code 410 -
      "Incorrect identifier" shall be returned in these cases.
   
   
   7  COMMANDS
   
      The protocol provides commands for manipulating the logical entities
      of the protocol connection model, Contexts and Terminations. Commands
      provide control at the finest level of granularity supported by the
      protocol. For example, Commands exist to add Terminations to a
      Context, modify Terminations, subtract Terminations from a Context,
      and audit properties of Contexts or Terminations. Commands provide
      for complete control of the properties of Contexts and Terminations.
      This includes specifying which events a Termination is to report,
      which signals/actions are to be applied to a Termination and
      specifying the topology of a Context (who hears/sees whom).
   
      Most commands are for the specific use of the Media Gateway
      Controller as command initiator in controlling Media Gateways as
      command responders. The exceptions are the Notify and ServiceChange
      commands: Notify is sent from Media Gateway to Media Gateway
      Controller, and ServiceChange may be sent by either entity. Below is
      an overview of the commands; they are explained in more detail in
      7.2.
   
      1) Add: The Add command adds a Termination to a Context. The Add
         command on the first Termination in a Context is used to create a
         Context.
   
      2) Modify: The Modify command modifies the properties, events and
         signals of a Termination.
   
   
   
   
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      3) Subtract: The Subtract command disconnects a Termination from its
         Context and returns statistics on the Termination's participation
         in the Context. The Subtract command on the last Termination in a
         Context deletes the Context.
   
      4) Move: The Move command atomically moves a Termination to another
         Context.
   
      5) AuditValue: The AuditValue command returns the current state of
         properties, events, signals and statistics of Terminations.
   
      6) AuditCapabilities: The AuditCapabilities command returns all the
         possible values for Termination properties, events and signals
         allowed by the Media Gateway.
   
      7) Notify: The Notify command allows the Media Gateway to inform the
         Media Gateway Controller of the occurrence of events in the Media
         Gateway.
   
      8) ServiceChange: The ServiceChange command allows the Media Gateway
         to notify the Media Gateway Controller that a Termination or group
         of Terminations is about to be taken out of service or has just
         been returned to service. ServiceChange is also used by the MG to
         announce its availability to a MGC (registration), and to notify
         the MGC of impending or completed restart of the MG. The MGC may
         announce a handover to the MG by sending it a ServiceChange
         command. The MGC may also use ServiceChange to instruct the MG to
         take a Termination or group of Terminations in or out of service.
   
      These commands are detailed in 7.2.1 through 7.2.8.
   
   7.1   Descriptors
   
      The parameters to a command are termed Descriptors. A descriptor
      consists of a name and a list of items. Some items may have values.
      Many Commands share common descriptors. This subclause enumerates
      these descriptors. Descriptors may be returned as output from a
      command. In any such return of descriptor contents, an empty
      descriptor is represented by its name unaccompanied by any list.
      Parameters and parameter usage specific to a given Command type are
      described in the subclause that describes the Command.
   
   7.1.1 Specifying parameters
   
      Command parameters are structured into a number of descriptors. In
      general, the text format of descriptors is
         DescriptorName=<someID>{parm=value, parm=value, ...}.
   
      Parameters may be fully specified, overspecified or underspecified:
   
   
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      1) Fully specified parameters have a single, unambiguous value that
         the command initiator is instructing the command responder to use
         for the specified parameter.
   
      2) Underspecified parameters, using the CHOOSE value, allow the
         command responder to choose any value it can support.
   
      3) Overspecified parameters have a list of potential values. The list
         order specifies the command initiator's order of preference of
         selection. The command responder chooses one value from the
         offered list and returns that value to the command initiator.
   
      If a required descriptor other than the Audit descriptor is
      unspecified (i.e. entirely absent) from a command, the previous
      values set in that descriptor for that Termination, if any, are
      retained. In commands other than Subtract, a missing Audit descriptor
      is equivalent to an empty Audit descriptor. The Behaviour of the MG
      with respect to unspecified parameters within a descriptor varies
      with the descriptor concerned, as indicated in succeeding subclauses.
      Whenever a parameter is underspecified or overspecified, the
      descriptor containing the value chosen by the responder is included
      as output from the command.
   
      Each command specifies the TerminationId the command operates on.
      This TerminationId may be "wildcarded". When the TerminationId of a
      command is wildcarded, the effect shall be as if the command was
      repeated with each of the TerminationIds matched.
   
   7.1.2 Modem descriptor
   
      The Modem descriptor specifies the modem type and parameters, if any,
      required for use in e.g. H.324 and text conversation. The descriptor
      includes the following modem types: V.18, V.22, V.22 bis, V.32, V.32
      bis, V.34, V.90, V.91, Synchronous ISDN, and allows for extensions.
      By default, no Modem descriptor is present in a Termination.
   
      Use of the ModemDescriptor is deprecated in Megaco v2/H.248.1
      (05/2002) and subsequent versions. This means that the
      ModemDescriptor shall not be included as part of transmitted content
      and if received shall either be ignored or processed at the option of
      the implementation. Modem type is to be specified as an attribute of
      data streams in LocalDescriptor and RemoteDescriptor.
   
   7.1.3 Multiplex descriptor
   
      In multimedia calls, a number of media streams are carried on a
      (possibly different) number of bearers. The multiplex descriptor
      associates the media and the bearers. The descriptor includes the
      multiplex type:
   
   
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      -  H.221;
      -  H.223;
      -  H.226;
      -  V.76;
      -  Nx64K;
      -  possible extensions,
   
      and a set of TerminationIDs representing the multiplexed bearers, in
      order. For example:
   
         Mux = H.221{ MyT3/1/2, MyT3/2/13, MyT3/3/6, MyT3/21/22}
   
      The Nx64K Multiplex type implements the Nx64K service (e.g. as
      defined by Q.931 Information Transfer Rate or Q.763 Transmission
      Medium Requirement). On the context side it supports a single stream
      of wideband data.  When a bearer termination is added implicitly to a
      context as a result of the creation of an Nx64K multiplexing
      termination, the streamDescriptor for the bearer termination shall
      take on the same values as the streamDescriptor defined for the
      Multiplex termination, except that the bearer termination bandwidth
      shall be 64 kilobits per second.
   
   7.1.4 Media descriptor
   
      The Media descriptor specifies the parameters for all the media
      streams. These parameters are structured into two descriptors: a
      TerminationState descriptor, which specifies the properties of a
      Termination that are not stream dependent, and one or more Stream
      descriptors each of which describes a single media stream.
   
      A stream is identified by a StreamID. The StreamID is used to link
      the streams in a Context that belong together. Multiple streams
      exiting a Termination shall be synchronized with each other. Within
      the Stream descriptor, there are up to three subsidiary descriptors:
      LocalControl, Local, and Remote. The relationship between these
      descriptors is thus:
   
      Media descriptor
         TerminationState Descriptor
         Stream descriptor
            LocalControl descriptor
            Local descriptor
            Remote descriptor
   
      As a convenience, LocalControl, Local, or Remote descriptors may be
      included in the Media descriptor without an enclosing Stream
      descriptor. In this case, the StreamID is assumed to be 1.
   
   
   
   
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   7.1.5 TerminationState descriptor
   
      The TerminationState descriptor contains the ServiceStates property,
      the EventBufferControl property and properties of a Termination
      (defined in Packages) that are not stream specific.
   
      The ServiceStates property describes the overall state of the
      Termination (not stream specific). A Termination can be in one of the
      following states: "test", "out of service", or "in service". The
      "test" state indicates that the Termination is being tested. The
      state "out of service" indicates that the Termination cannot be used
      for traffic. The state "in service" indicates that a Termination can
      be used or is being used for normal traffic. "in service" is the
      default state.
   
      Values assigned to Properties may be simple values
      (integer/string/enumeration) or may be underspecified, where more
      than one value is supplied and the MG may make a choice:
   
      -  Alternative Values - multiple values in a list, one of which must
         be selected
   
      -  Ranges - minimum and maximum values, any value between min and max
         must be selected, boundary values included
   
      -  Greater Than/Less Than - value must be greater/less than specified
         value
   
      -  CHOOSE Wildcard - the MG chooses from the allowed values for the
         property
   
      The EventBufferControl property specifies whether events are buffered
      following detection of an event in the Events descriptor, or
      processed immediately. See 7.1.9 for details.
   
   7.1.6 Stream descriptor
   
      A Stream descriptor specifies the parameters of a single
      bidirectional stream. These parameters are structured into three
      descriptors: one that contains Termination properties specific to a
      stream and one each for local and remote flows. The Stream Descriptor
      includes a StreamID which identifies the stream. Streams are created
      by specifying a new StreamID on one of the Terminations in a Context.
      A stream is deleted by setting empty Local and Remote descriptors for
      the stream with ReserveGroup and ReserveValue in LocalControl set to
      "false" on all Terminations in the Context that previously supported
      that stream.
   
   
   
   
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      StreamIDs are of local significance between MGC and MG and they are
      assigned by the MGC. Within a Context, StreamID is a means by which
      to indicate which media flows are interconnected: streams with the
      same StreamID are connected.
   
      If a Termination is moved from one Context to another, the effect on
      the Context to which the Termination is moved is the same as in the
      case that a new Termination were added with the same StreamIDs as the
      moved Termination.
   
   7.1.7 LocalControl descriptor
   
      The LocalControl descriptor contains the Mode property, the
      ReserveGroup and ReserveValue properties and properties of a
      Termination (defined in Packages) that are stream specific, and are
      of interest between the MG and the MGC. Values of properties may be
      specified as in 7.1.1.
   
      The allowed values for the mode property are send-only, receive-only,
      send/receive, inactive and loop-back. "Send" and "receive" are with
      respect to the exterior of the Context, so that, for example, a
      stream set to mode=sendOnly does not pass received media into the
      Context. The default value for the mode property is "Inactive".
      Signals and Events are not affected by mode.
   
      The boolean-valued Reserve properties, ReserveValue and ReserveGroup,
      of a Termination indicate what the MG is expected to do when it
      receives a Local and/or Remote descriptor.
   
      If the value of a Reserve property is True, the MG SHALL reserve
      resources for all alternatives specified in the Local and/or Remote
      descriptors for which it currently has resources available. It SHALL
      respond with the alternatives for which it reserves resources. If it
      cannot not support any of the alternatives, it SHALL respond with a
      reply to the MGC that contains empty Local and/or Remote descriptors.
      If media begins to flow while more than a single alternative is
      reserved, media packets may be sent/received on any of the
      alternatives and must be processed, although only a single
      alternative may be active at any given time.
   
      If the value of a Reserve property is False, the MG SHALL choose one
      of the alternatives specified in the Local descriptor (if present)
      and one of the alternatives specified in the Remote descriptor (if
      present). If the MG has not yet reserved resources to support the
      selected alternative, it SHALL reserve the resources. If, on the
      other hand, it already reserved resources for the Termination
      addressed (because of a prior exchange with ReserveValue and/or
      ReserveGroup equal to True), it SHALL release any excess resources it
      reserved previously. Finally, the MG shall send a reply to the MGC
   
   
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      containing the alternatives for the Local and/or Remote descriptor
      that it selected. If the MG does not have sufficient resources to
      support any of the alternatives specified, is SHALL respond with
      Error 510 - "Insufficient resources".
   
      The default value of ReserveValue and ReserveGroup is False. More
      information on the use of the two Reserve properties is provided in
      7.1.8.
   
      A new setting of the LocalControl Descriptor completely replaces the
      previous setting of that descriptor in the MG. Thus, to retain
      information from the previous setting, the MGC must include that
      information in the new setting. If the MGC wishes to delete some
      information from the existing descriptor, it merely resends the
      descriptor (in a Modify command) with the unwanted information
      stripped out.
   
   7.1.8 Local and Remote descriptors
   
      The MGC uses Local and Remote descriptors to reserve and commit MG
      resources for media decoding and encoding for the given Stream(s) and
      Termination to which they apply. The MG includes these descriptors in
      its response to indicate what it is actually prepared to support. The
      MG SHALL include additional properties and their values in its
      response if these properties are mandatory yet not present in the
      requests made by the MGC (e.g. by specifying detailed video encoding
      parameters where the MGC only specified the payload type).
   
      Local refers to the media received by the MG and Remote refers to the
      media sent by the MG.
   
      When text encoding the protocol, the descriptors consist of session
      descriptions as defined in SDP (RFC 2327). In session descriptions
      sent from the MGC to the MG, the following exceptions to the syntax
      of RFC 2327 are allowed:
   
      -  the "s=", "t=" and "o=" lines are optional;
   
      -  the use of CHOOSE is allowed in place of a single parameter value;
         and
   
      -  the use of alternatives is allowed in place of a single parameter
         value.
   
      A Stream Descriptor specifies a single bi-directional media stream
      and so a single session description MUST NOT include more than one
      media description ("m=" line). A Stream Descriptor may contain
      additional session descriptions as alternatives.  Each media stream
      for a termination must appear in distinct Stream Descriptors. When
   
   
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      multiple session descriptions are provided in one descriptor, the
      "v=" lines are required as delimiters; otherwise they are optional in
      session descriptions sent to the MG. Implementations shall accept
      session descriptions that are fully conformant to RFC 2327. When
      binary encoding the protocol the descriptor consists of groups of
      properties (tag-value pairs) as specified in Annex C. Each such group
      may contain the parameters of a session description.
   
      Below, the semantics of the Local and Remote descriptors are
      specified in detail. The specification consists of two parts. The
      first part specifies the interpretation of the contents of the
      descriptor. The second part specifies the actions the MG must take
      upon receiving the Local and Remote descriptors. The actions to be
      taken by the MG depend on the values of the ReserveValue and
      ReserveGroup properties of the LocalControl descriptor.
   
      Either the Local or the Remote descriptor or both may be:
   
      -  unspecified (i.e. absent);
   
      -  empty;
   
      -  underspecified through use of CHOOSE in a property value;
   
      -  fully specified; or
   
      -  overspecified through presentation of multiple groups of
         properties and possibly multiple property values in one or more of
         these groups.
   
      Where the descriptors have been passed from the MGC to the MG, they
      are interpreted according to the rules given in 7.1.1, with the
      following additional comments for clarification:
   
      a) An unspecified Local or Remote descriptor is considered to be a
         missing mandatory parameter. It requires the MG to use whatever
         was last specified for that descriptor. It is possible that there
         was no previously specified value, in which case the descriptor
         concerned is ignored in further processing of the command.
   
      b) An empty Local (Remote) descriptor in a message from the MGC
         signifies a request to release any resources reserved for the
         media flow received (sent).
   
      c) If multiple groups of properties are present in a Local or Remote
         descriptor or multiple values within a group, the order of
         preference is descending.
   
   
   
   
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      d) Underspecified or overspecified properties within a group of
         properties sent by the MGC are requests for the MG to choose one
         or more values which it can support for each of those properties.
         In case of an overspecified property, the list of values is in
         descending order of preference.
   
      Subject to the above rules, subsequent action depends on the values
      of the ReserveValue and ReserveGroup properties in LocalControl.
   
      If ReserveGroup is True, the MG reserves the resources required to
      support any of the requested property group alternatives that it can
      currently support. If ReserveValue is True, the MG reserves the
      resources required to support any of the requested property value
      alternatives that it can currently support.
   
      NOTE - If a Local or Remote descriptor contains multiple groups of
      properties, and ReserveGroup is True, then the MG is requested to
      reserve resources so that it can decode or encode the media stream
      according to any of the alternatives. For instance, if the Local
      descriptor contains two groups of properties, one specifying
      packetized G.711 A-law audio and the other G.723.1 audio, the MG
      reserves resources so that it can decode one audio stream encoded in
      either G.711 A-law format or G.723.1 format. The MG does not have to
      reserve resources to decode two audio streams simultaneously, one
      encoded in G.711 A-law and one in G.723.1. The intention for the use
      of ReserveValue is analogous.
   
      If ReserveGroup is true or ReserveValue is True, then the following
      rules apply:
   
      -  If the MG has insufficient resources to support all alternatives
         requested by the MGC and the MGC requested resources in both Local
         and Remote, the MG SHOULD reserve resources to support at least
         one alternative each within Local and Remote.
   
      -  If the MG has insufficient resources to support at least one
         alternative within a Local (Remote) descriptor received from the
         MGC, it shall return an empty Local (Remote) in response.
   
      -  In its response to the MGC, when the MGC included Local and Remote
         descriptors, the MG SHALL include Local and Remote descriptors for
         all groups of properties and property values it reserved resources
         for. If the MG is incapable of supporting at least one of the
         alternatives within the Local (Remote) descriptor received from
         the MGC, it SHALL return an empty Local (Remote) descriptor.
   
      -  If the Mode property of the LocalControl descriptor is RecvOnly,
         SendRecv, or LoopBack, the MG must be prepared to receive media
   
   
   
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         encoded according to any of the alternatives included in its
         response to the MGC.
   
      If ReserveGroup is False and ReserveValue is False, then the MG
      SHOULD apply the following rules to resolve Local and Remote to a
      single alternative each:
   
      -  The MG chooses the first alternative in Local for which it is able
         to support at least one alternative in Remote.
   
      -  If the MG is unable to support at least one Local and one Remote
         alternative, it returns Error 510 - "Insufficient resources".
   
      -  The MG returns its selected alternative in each of Local and
         Remote.
   
      A new setting of a Local or Remote descriptor completely replaces the
      previous setting of that descriptor in the MG. Thus, to retain
      information from the previous setting, the MGC must include that
      information in the new setting. If the MGC wishes to delete some
      information from the existing descriptor, it merely resends the
      descriptor (in a Modify command) with the unwanted information
      stripped out.
   
   7.1.9 Events descriptor
   
      The EventsDescriptor parameter contains a RequestIdentifier and a
      list of events that the Media Gateway is requested to detect and
      report. The RequestIdentifier is used to correlate the request with
      the notifications that it may trigger. Requested events include, for
      example, fax tones, continuity test results, and on-hook and off-hook
      transitions. The RequestIdentifier is omitted if the EventsDescriptor
      is empty (i.e. no events are specified).
   
      Each event in the descriptor contains the Event name, an optional
      streamID, an optional KeepActive flag, and optional parameters. The
      Event name consists of a Package Name (where the event is defined)
      and an EventID. The ALL wildcard may be used for the EventID,
      indicating that all events from the specified package have to be
      detected. The default streamID is 0, indicating that the event to be
      detected is not related to a particular media stream. Events can have
      parameters. This allows a single event description to have some
      variation in meaning without creating large numbers of individual
      events. Further event parameters are defined in the package.
   
      If a digit map completion event is present or implied in the
      EventsDescriptor, the EventDM parameter is used to carry either the
      name or the value of the associated digit map. See 7.1.14 for further
      details.
   
   
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      When an event is processed against the contents of an active Events
      Descriptor and found to be present in that descriptor ("recognized"),
      the default action of the MG is to send a Notify command to the MGC.
      Notification may be deferred if the event is absorbed into the
      current dial string of an active digit map (see 7.1.14). Any other
      action is for further study. Moreover, event recognition may cause
      currently active signals to stop, or may cause the current Events
      and/or Signals descriptor to be replaced, as described at the end of
      this subclause. Unless the Events Descriptor is replaced by another
      Events Descriptor, it remains active after an event has been
      recognized.
   
      If the value of the EventBufferControl property equals LockStep,
      following detection of such an event, normal handling of events is
      suspended. Any event which is subsequently detected and occurs in the
      EventBuffer descriptor is added to the end of the EventBuffer (a FIFO
      queue), along with the time that it was detected. The MG SHALL wait
      for a new EventsDescriptor to be loaded. A new EventsDescriptor can
      be loaded either as the result of receiving a command with a new
      EventsDescriptor, or by activating an embedded EventsDescriptor.
   
      If EventBufferControl equals Off, the MG continues processing based
      on the active EventsDescriptor.
   
      In the case of an embedded EventsDescriptor being activated, the MG
      continues event processing based on the newly activated
      EventsDescriptor.
   
      NOTE 1 - For purposes of EventBuffer handling, activation of an
      embedded EventsDescriptor is equivalent to receipt of a new
      EventsDescriptor.
   
      When the MG receives a command with a new EventsDescriptor, one or
      more events may have been buffered in the EventBuffer in the MG. The
      value of EventBufferControl then determines how the MG treats such
      buffered events.
   
   
      Case 1
   
      If EventBufferControl equals LockStep and the MG receives a new
      EventsDescriptor, it will check the FIFO EventBuffer and take the
      following actions:
   
      1) If the EventBuffer is empty, the MG waits for detection of events
         based on the new EventsDescriptor.
   
      2) If the EventBuffer is non-empty, the MG processes the FIFO queue
         starting with the first event:
   
   
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         a) If the event in the queue is in the events listed in the new
            EventsDescriptor, the MG acts on the event and removes the
            event from the EventBuffer. The time stamp of the Notify shall
            be the time the event was actually detected. The MG then waits
            for a new EventsDescriptor. While waiting for a new
            EventsDescriptor, any events detected that appear in the
            EventsBufferDescriptor will be placed in the EventBuffer. When
            a new EventsDescriptor is received, the event processing will
            repeat from step 1.
   
         b) If the event is not in the new EventsDescriptor, the MG SHALL
            discard the event and repeat from step 1.
   
   
      Case 2
   
      If EventBufferControl equals Off and the MG receives a new
      EventsDescriptor, it processes new events with the new
      EventsDescriptor.
   
      If the MG receives a command instructing it to set the value of
      EventBufferControl to Off, all events in the EventBuffer SHALL be
      discarded.
   
      The MG may report several events in a single Transaction as long as
      this does not unnecessarily delay the reporting of individual events.
   
      For procedures regarding transmitting the Notify command, refer to
      the appropriate annex or Recommendation of the H.248 sub-series for
      specific transport considerations.
   
      The default value of EventBufferControl is Off.
   
      NOTE 2 - Since the EventBufferControl property is in the
      TerminationStateDescriptor, the MG might receive a command that
      changes the EventBufferControl property and does not include an
      EventsDescriptor.
   
      Normally, recognition of an event shall cause any active signals to
      stop. When KeepActive is specified in the event, the MG shall not
      interrupt any signals active on the Termination on which the event is
      detected.
   
      An event can include an Embedded Signals descriptor and/or an
      Embedded Events descriptor which, if present, replaces the current
      Signals/Events descriptor when the event is recognized. It is
      possible, for example, to specify that the dial-tone Signal be
      generated when an off-hook Event is recognized, or that the dial-tone
      Signal be stopped when a digit is recognized. A media gateway
   
   
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      controller shall not send EventsDescriptors with an event both marked
      KeepActive and containing an embedded SignalsDescriptor.
   
      Only one level of embedding is permitted. An embedded
      EventsDescriptor SHALL NOT contain another embedded EventsDescriptor;
      an embedded EventsDescriptor MAY contain an embedded
      SignalsDescriptor.
   
      An EventsDescriptor received by a media gateway replaces any previous
      Events descriptor. Event notification in process shall complete, and
      events detected after the command containing the new EventsDescriptor
      executes, shall be processed according to the new EventsDescriptor.
   
      An empty Events Descriptor disables all event recognition and
      reporting.  An empty EventBuffer Descriptor clears the EventBuffer
      and disables all event accumulation in LockStep mode: the only events
      reported will be those occurring while an Events Descriptor is
      active.  If an empty Events Descriptor is activated while the
      Termination is operating in LockStep mode, the events buffer is
      immediately cleared.
   
   7.1.10   EventBuffer descriptor
   
      The EventBuffer descriptor contains a list of events, with their
      parameters if any, that the MG is requested to detect and buffer when
      EventBufferControl equals LockStep (see 7.1.9).
   
   7.1.11   Signals descriptor
   
      Signals are MG generated media such as tones and announcements as
      well as bearer-related signals such as hookswitch. More complex
      signals may include a sequence of such simple signals interspersed
      with and conditioned upon the receipt and analysis of media or
      bearer-related signals. Examples include echoing of received data as
      in Continuity Test package.  Signals may also request preparation of
      media content for future signals.
   
      A SignalsDescriptor is a parameter that contains the set of signals
      that the Media Gateway is asked to apply to a Termination. A
      SignalsDescriptor contains a number of signals and/or sequential
      signal lists. A SignalsDescriptor may contain zero signals and
      sequential signal lists. Support of sequential signal lists is
      optional.
   
      Signals are defined in packages. Signals shall be named with a
      Package name (in which the signal is defined) and a SignalID. No
      wildcard shall be used in the SignalID. Signals that occur in a
      SignalsDescriptor have an optional StreamID parameter (default is 0,
      to indicate that the signal is not related to a particular media
   
   
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      stream), an optional signal type (see below), an optional duration
      and possibly parameters defined in the package that defines the
      signal. This allows a single signal to have some variation in
      meaning, obviating the need to create large numbers of individual
      signals.
   
      Finally, the optional parameter "notifyCompletion" allows a MGC to
      indicate that it wishes to be notified when the signal finishes
      playout. The possible cases are that the signal timed out (or
      otherwise completed on its own), that it was interrupted by an event,
      that it was halted when a Signals descriptor was replaced, or that it
      stopped or never started for other reasons. If the notifyCompletion
      parameter is not included in a Signals descriptor, notification is
      generated only if the signal stopped or was never started for other
      reasons. For reporting to occur, the signal completion event (see
      E.1.2) must be enabled in the currently active Events descriptor.
   
      The duration is an integer value that is expressed in hundredths of a
      second.
   
      There are three types of signals:
   
      -  on/off - the signal lasts until it is turned off;
   
      -  timeout - the signal lasts until it is turned off or a specific
         period of time elapses;
   
      -  brief - the signal will stop on its own unless a new Signals
         descriptor is applied that causes it to stop; no timeout value is
         needed.
   
      If a signal of default type other than TO has its type overridden to
      type TO in the Signals descriptor, the duration parameter must be
      present.
   
      If the signal type is specified in a SignalsDescriptor, it overrides
      the default signal type (see 12.1.4). If duration is specified for an
      on/off signal, it SHALL be ignored.
   
      A sequential signal list consists of a signal list identifier and a
      sequence of signals to be played sequentially. Only the trailing
      element of the sequence of signals in a sequential signal list may be
      an on/off signal. The duration of a sequential signal list is the sum
      of the durations of the signals it contains.
   
      Multiple signals and sequential signal lists in the same
      SignalsDescriptor shall be played simultaneously.
   
   
   
   
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      Signals are defined as proceeding from the Termination towards the
      exterior of the Context unless otherwise specified in a package. When
      the same Signal is applied to multiple Terminations within one
      Transaction, the MG SHOULD consider using the same resource to
      generate these Signals.
   
      Production of a Signal on a Termination is stopped by application of
      a new SignalsDescriptor, or detection of an Event on the Termination
      (see 7.1.9).
   
      A new SignalsDescriptor replaces any existing SignalsDescriptor. Any
      signals applied to the Termination not in the replacement descriptor
      shall be stopped, and new signals are applied, except as follows.
      Signals present in the replacement descriptor and containing the
      KeepActive flagshall be continued if they are currently playing and
      have not already completed. If a replacement signal descriptor
      contains a signal that is not currently playing and contains the
      KeepActive flag, that signal SHALL be ignored. If the replacement
      descriptor contains a sequential signal list with the same identifier
      as the existing descriptor, then
   
      -  the signal type and sequence of signals in the sequential signal
         list in the replacement descriptor shall be ignored; and
   
      -  the playing of the signals in the sequential signal list in the
         existing descriptor shall not be interrupted.
   
   7.1.12   Audit descriptor
   
      The Audit descriptor specifies what information is to be audited. The
      Audit descriptor specifies the list of descriptors and-or individual
      properties to be returned. Audit may be used in any command to force
      the return of any descriptor containing the current values of its
      properties, events, signals and statistics even if that descriptor
      was not present in the command, or had no underspecified parameters.
      Possible items in the Audit descriptor are:
   
      -  Modem (Deprecated, see clause 7.1.2)
      -  Mux
      -  Events
      -  Media
      -  Signals
      -  ObservedEvents
      -  DigitMap
      -  Statistics
      -  Packages
      -  EventBuffer
      -  Individual Audit Items:
         -  Media Properties
   
   
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         -  Events
         -  Event Buffer
         -  Signals, Signal Lists
         -  Digit Maps
         -  Statistics
         -  Packages
   
      Audit may be empty, in which case, no descriptors are returned. This
      is useful in Subtract, to inhibit return of statistics, especially
      when using wildcard.
   
   7.1.13   ServiceChange descriptor
   
      The ServiceChangeDescriptor contains the following parameters:
   
      -  ServiceChangeMethod
      -  ServiceChangeReason
      -  ServiceChangeAddress
      -  ServiceChangeDelay
      -  ServiceChangeProfile
      -  ServiceChangeVersion
      -  ServiceChangeMGCId
      -  TimeStamp
      -  Extension
   
      See 7.2.8.
   
   7.1.14   DigitMap descriptor
   
   7.1.14.1 DigitMap definition, creation, modification and deletion
   
      A DigitMap is a dialing plan resident in the Media Gateway used for
      detecting and reporting digit events received on a Termination. The
      DigitMap descriptor contains a DigitMap name and the DigitMap to be
      assigned. A digit map may be preloaded into the MG by management
      action and referenced by name in an EventsDescriptor, may be defined
      dynamically and subsequently referenced by name, or the actual
      digitmap itself may be specified in the EventsDescriptor. It is
      permissible for a digit map completion event within an Events
      descriptor to refer by name to a DigitMap which is defined by a
      DigitMap descriptor within the same command, regardless of the
      transmitted order of the respective descriptors.
   
      DigitMaps defined in a DigitMapDescriptor can occur in any of the
      standard Termination manipulation Commands of the protocol. A
      DigitMap, once defined, can be used on all Terminations specified by
      the (possibly wildcarded) TerminationID in such a command. DigitMaps
      defined on the root Termination are global and can be used on every
      Termination in the MG, provided that a DigitMap with the same name
   
   
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      has not been defined on the given Termination. When a DigitMap is
      defined dynamically in a DigitMap descriptor:
   
      -  A new DigitMap is created by specifying a name that is not yet
         defined. The value shall be present.
   
      -  A DigitMap value is updated by supplying a new value for a name
         that is already defined. Terminations presently using the digitmap
         shall continue to use the old definition; subsequent
         EventsDescriptors specifying the name, including any
         EventsDescriptor in the command containing the DigitMap
         descriptor, shall use the new one.
   
      -  A DigitMap is deleted by supplying an empty value for a name that
         is already defined. Terminations presently using the digitmap
         shall continue to use the old definition.
   
   7.1.14.2 DigitMap Timers
   
      The collection of digits according to a DigitMap may be protected by
      three timers, viz. a start timer (T), short timer (S), and long timer
      (L).
   
      1) The start timer (T) is used prior to any digits having been
         dialed. If the start timer is overridden with the value set to
         zero (T=0), then the start timer shall be disabled.  This implies
         that the MG will wait indefinitely for digits.
   
      2) If the Media Gateway can determine that at least one more digit is
         needed for a digit string to match any of the allowed patterns in
         the digit map, then the interdigit timer value SHOULD be set to a
         long (L) duration (e.g. 16 seconds).
   
      3) If the digit string has matched one of the patterns in a digit
         map, but it is possible that more digits could be received which
         would cause a match with a different pattern, then instead of
         reporting the match immediately, the MG must apply the short timer
         (S) and wait for more digits.
   
      The timers are configurable parameters to a DigitMap. Default values
      of these timers SHOULD be provisioned on the MG, but can be
      overridden by values specified within the DigitMap.
   
   7.1.14.3 DigitMap Syntax
   
      The formal syntax of the digit map is described by the DigitMap rule
      in the formal syntax description of the protocol (see Annex A and
      Annex B). A DigitMap, according to this syntax, is defined either by
      a string or by a list of strings. Each string in the list is an
   
   
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      alternative event sequence, specified either as a sequence of digit
      map symbols or as a regular expression of digit map symbols. These
      digit map symbols, the digits "0" through "9" and letters "A" through
      a maximum value depending on the signalling system concerned, but
      never exceeding "K", correspond to specified events within a package
      which has been designated in the Events descriptor on the Termination
      to which the digit map is being applied. (The mapping between events
      and digit map symbols is defined in the documentation for packages
      associated with channel-associated signalling systems such as DTMF,
      MF, or R2. Digits "0" through "9" MUST be mapped to the corresponding
      digit events within the signalling system concerned. Letters SHOULD
      be allocated in logical fashion, facilitating the use of range
      notation for alternative events.)
   
      The letter "x" is used as a wildcard, designating any event
      corresponding to symbols in the range "0"-"9". The string may also
      contain explicit ranges and, more generally, explicit sets of
      symbols, designating alternative events any one of which satisfies
      that position of the digit map. Finally, the dot symbol "." stands
      for zero or more repetitions of the event selector (event, range of
      events, set of alternative events, or wildcard) that precedes it. As
      a consequence of the third timing rule above, inter-event timing
      while matching a terminal dot symbol uses the short timer by default.
   
      In addition to these event symbols, the string may contain "S" and
      "L" inter-event timing specifiers and the "Z" duration modifier. "S"
      and "L" respectively indicate that the MG SHOULD use the short (S)
      timer or the long (L) timer for subsequent events, overriding the
      timing rules described above. If an explicit timing specifier is in
      effect in one alternative event sequence, but none is given in any
      other candidate alternative, the timer value set by the explicit
      timing specifier must be used. If all sequences with explicit timing
      controls are dropped from the candidate set, timing reverts to the
      default rules given above. Finally, if conflicting timing specifiers
      are in effect in different alternative sequences, the long timer
      shall be used.
   
      A "Z" designates a long duration event: placed in front of the
      symbol(s) designating the event(s) which satisfy a given digit
      position, it indicates that that position is satisfied only if the
      duration of the event exceeds the long-duration threshold. The value
      of this threshold is assumed to be provisioned in the MG, but, like
      the T, L, and S timers, can be overridden by specification within the
      DigitMap.
   
   7.1.14.4 DigitMap Completion Event
   
      A digit map is active while the Events descriptor which invoked it is
      active and it has not completed. A digit map completes when:
   
   
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      -  a timer has expired; or
   
      -  an alternative event sequence has been matched and no other
         alternative event sequence in the digit map could be matched
         through detection of an additional event (unambiguous match); or
   
      -  an event has been detected such that a match to a complete
         alternative event sequence of the digit map will be impossible no
         matter what additional events are received.
   
      Upon completion, a digit map completion event as defined in the
      package providing the events being mapped into the digit map shall be
      generated. At that point the digit map is deactivated. Subsequent
      events in the package are processed as follows:
   
      -  If EventBufferControl is ON, subsequent digit events are processed
         in the same way as any other events;
   
      -  If EventBufferControl is OFF, if the active EventsDescriptor did
         not change, and if individual digit events are not enabled within
         that descriptor, then digit buffering will be initiated.
         Buffering will continue until the buffering time specified in the
         original digit map completion event has expired or until the
         active EventsDescriptor is replaced.
   
      The digit buffer shall take the logical form of a dial string which
      includes the digit characters as represented in the digit map,
      possibly preceded by 'Z'.  The threshold value of tone duration used
      to identify long events shall be the same as that used with the most
      recently completed digit map.
   
      Buffering time defaults to zero (no buffering) unless explicitly set
      otherwise within the digit map completion event.  If buffering ceases
      due to buffering timer expiry, the contents of the digit buffer are
      discarded.
   
      If buffering was stopped by a new EventsDescriptor, then if that
      EventsDescriptor contains a new digit map completion event from the
      same package as the previous one, any buffered digits are processed
      against the digit map as described below.  Buffered digits not
      consumed by the new digit map are handled as if they had were
      observed after that map completed.
   
      If instead the new EventsDescriptor enables the reporting of
      individual digit events, the entire set of buffered digits shall
      immediately be processed, the applicable events reported, and the
      buffer cleared.
   
   
   
   
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      Finally, if the new EventsDescriptor enables neither a digit map
      completion event nor the reporting of individual digit events from
      the package concerned, the buffer contents are discarded and
      buffering is terminated.
   
   7.1.14.5 DigitMap Procedures
   
      Pending completion, successive events shall be processed according to
      the following rules:
   
      1) The "current dial string", an internal variable, is initially
         empty. The set of candidate alternative event sequences includes
         all of the alternatives specified in the digit map.
   
      2) At each step, if buffered digits are available, the oldest one
         (with possible accompanying long digit (Z) qualifier) is removed
         from the buffer and processing moves to the next step as if the
         digit event had just been observed. Otherwise a timer is set to
         wait for the next event, based either on the default timing rules
         given above or on explicit timing specified in one or more
         alternative event sequences. If the timer expires and a member of
         the candidate set of alternatives is fully satisfied, a timeout
         completion with full match is reported. If the timer expires and
         part or none of any candidate alternative is satisfied, a timeout
         completion with partial match is reported. In either case, if the
         digit map completion event allows for detailed timeout reporting,
         the reported dial string will end with 'L', 'S', or 'T' as
         appropriate.
   
      3) If an event is detected before the timer expires, it is mapped to
         a digit string symbol and provisionally added to the end of the
         current dial string. The duration of the event (long or not long)
         is noted if and only if this is relevant in the current symbol
         position (because at least one of the candidate alternative event
         sequences includes the "Z" modifier at this position in the
         sequence).
   
      4) The current dial string is compared to the candidate alternative
         event sequences. If and only if a sequence expecting a long-
         duration event at this position is matched (i.e. the event had
         long duration and met the specification for this position), then
         any alternative event sequences not specifying a long duration
         event at this position are discarded, and the current dial string
         is modified by inserting a "Z" in front of the symbol representing
         the latest event. Any sequence expecting a long-duration event at
         this position but not matching the observed event is discarded
         from the candidate set. If alternative event sequences not
         specifying a long duration event in the given position remain in
         the candidate set after application of the above rules, the
   
   
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         observed event duration is treated as irrelevant in assessing
         matches to them.
   
      5) If exactly one candidate remains and it has been fully matched, a
         completion event is generated indicating an unambiguous match. If
         no candidates remain, the latest event is removed from the current
         dial string and a completion event is generated indicating full
         match if one of the candidates from the previous step was fully
         satisfied before the latest event was detected, or partial match
         otherwise. The event removed from the current dial string will
         then be reported a separate event, buffered, or discarded
         according to the rules described in the previous section.  This
         statement is qualified as follows:
   
         a) The digit map completion event may specify that the removed
            event be reported as a parameter of the completion event.  This
            occurs independently of subsequent processing of the digit
            event.
   
         b) The digit map completion event may specify that the extra digit
            SHOULD be discarded.  In this case, it is discarded
            immediately.  Any buffering or other processing applies only to
            subsequent events.
   
      6) If no completion event is reported out of step 5, processing
         returns to step 2.
   
   7.1.14.6 DigitMap Activation
   
      A digit map is activated whenever a new Event descriptor is applied
      to the Termination or embedded Event descriptor is activated, that
      Event descriptor contains a digit map completion event. The digit map
      completion event contains an eventDM field in the requested actions
      field. Each new activation of a digit map begins at step 1 of the
      above procedure, with a clear current dial string. Any previous
      contents of the current dial string from an earlier activation are
      lost.
   
      A digit map completion event that does not contain an eventDM field
      in its requested actions field is considered an error.  Upon receipt
      of such an event in an EventsDescriptor, a MG shall respond with an
      error reponse, including Error 457 - "Missing parameter in signal or
      event".
   
   7.1.14.7 Interaction Of DigitMap and Event Processing
   
      While the digit map is activated, detection is enabled for all events
      defined in the package containing the specified digit map completion
      event. Normal event behaviour (e.g. stopping of signals unless the
   
   
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      digit completion event has the KeepActive flag enabled) continues to
      apply for each such event detected, except that:
   
      -  the events in the package containing the specified digit map
         completion event other than the completion event itself are not
         individually notified and have no side-effects unless separately
         enabled; and
   
      -  an event that triggers a partial match completion event is not
         recognized and therefore has no side effects until reprocessed
         following the recognition of the digit map completion event.
         Similarly buffered digit events are not recognized and have no
         side effects until processed.
   
   7.1.14.8 Wildcards
   
      Note that if a package contains a digit map completion event, then an
      event specification consisting of the package name with a wildcarded
      ItemID (Property Name) will activate a digit map; to that end, the
      event specification must include an eventDM field according to
      section 7.1.14.6. If the package also contains the digit events
      themselves, this form of event specification will cause the
      individual events to be reported to the MGC as they are detected.
   
   7.1.14.9 Example
   
      As an example, consider the following dial plan:
   
          0                          Local operator
   
          00                         Long-distance operator
   
          xxxx                       Local extension number (starts
                                     with 1-7)
   
          8xxxxxxx                   Local number
   
          #xxxxxxx                   Off-site extension
   
          *xx                        Star services
   
          91xxxxxxxxxx               Long-distance number
   
          9011 + up to 15 digits     International number
   
   
   
   
   
   
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      If the DTMF detection package described in E.6 is used to collect the
      dialled digits, then the dialling plan shown above results in the
      following digit map:
   
       (0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)
   
   7.1.15   Statistics descriptor
   
      The Statistics Descriptor provides information describing the status
      and usage of a Termination during its existence within a specific
      Context. There is a set of standard statistics kept for each
      Termination where appropriate (number of octets sent and received for
      example). The particular statistical properties that are reported for
      a given Termination are determined by the Packages realized by the
      Termination. By default, statistics are reported when the Termination
      is Subtracted from the Context. This behaviour can be overridden by
      including an empty AuditDescriptor in the Subtract command.
      Statistics may also be returned from the AuditValue command, or any
      Add/Move/Modify command using the Audit descriptor.
   
      Statistics are cumulative; reporting Statistics does not reset them.
      Statistics are reset when a Termination is Subtracted from a Context.
   
   7.1.16   Packages descriptor
   
      Used only with the AuditValue command, the PackageDescriptor returns
      a list of Packages realized by the Termination.
   
   7.1.17   ObservedEvents descriptor
   
      ObservedEvents is supplied with the Notify command to inform the MGC
      of which event(s) were detected. Used with the AuditValue command,
      the ObservedEventsDescriptor returns events in the event buffer which
      have not been Notified. ObservedEvents contains the RequestIdentifier
      of the EventsDescriptor that triggered the notification, the event(s)
      detected, optionally the detection time(s) and any parameters of the
      observed event. Detection times are reported with a precision of
      hundredths of a second.
   
   7.1.18   Topology descriptor
   
      A Topology descriptor is used to specify flow directions between
      Terminations in a Context. Contrary to the descriptors in previous
      subclauses, the Topology descriptor applies to a Context instead of a
      Termination. The default topology of a Context is that each
      Termination's transmission is received by all other Terminations. The
      Topology descriptor is optional to implement. An MG that does not
      support Topology descriptors, but receives a command containing one,
      returns Error 444 - "Unsupported or unknown descriptor", and
   
   
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      optionally includes a string containing the name of the unsupported
      Descriptor ("Topology") in the error text in the error descriptor.
   
      The Topology descriptor occurs before the commands in an action. It
      is possible to have an action containing only a Topology descriptor,
      provided that the Context to which the action applies already exists.
   
      A Topology descriptor consists of a sequence of tuples of associated
      terminations of the form (T1, T2, association[,StreamId]). T1 and T2
      specify Terminations within the Context, possibly using the ALL or
      CHOOSE wildcard. If the optional StreamId field is used, the
      association applies only to the particular stream between T1 and T2
      labeled by the StreamId. If the StreamId field is omitted, the
      topology applies to all streams in the termination. The association
      specifies how media flows between these two Terminations as follows.
   
      -  (T1, T2, isolate) means that the Terminations matching T2 do not
         receive media from the Terminations matching T1, nor vice versa.
   
      -  (T1, T2, oneway) means that the Terminations that match T2 receive
         media from the Terminations matching T1, but not vice versa. In
         this case use of the ALL wildcard such that there are Terminations
         that match both T1 and T2 is not allowed.
   
      -  (T1, T2, bothway) means that the Terminations matching T2 receive
         media from the Terminations matching T1, and vice versa. In this
         case it is allowed to use wildcards such that there are
         Terminations that match both T1 and T2. However, if there is a
         Termination that matches both, no loopback is introduced.
   
      CHOOSE wildcards may be used in T1 and T2 as well, under the
      following restrictions:
   
      -  the action (see clause 8) of which the topology descriptor is part
         contains an Add command in which a CHOOSE wildcard is used;
   
      -  if a CHOOSE wildcard occurs in T1 or T2, then a partial name SHALL
         NOT be specified.
   
      The CHOOSE wildcard in a Topology descriptor matches the
      TerminationID that the MG assigns in the first Add command that uses
      a CHOOSE wildcard in the same action. An existing Termination that
      matches T1 or T2 in the Context to which a Termination is added, is
      connected to the newly added Termination as specified by the Topology
      descriptor. If a termination is not mentioned within a topology
      descriptor, any topology associated with it remains unchanged. If,
      however, a new termination is added into a context its association
      with the other terminations within the context defaults to bothway,
      unless a topology descriptor is given to change this (eg. if T3 is
   
   
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      added to a context with T1 and T2 with topology (T3, T1, oneway) it
      will be connected bothway to T2).
   
      If the topology is applied to one particular stream (T1, T2,
      association, StreamId), the topology of other streams between the
      terminations does not change.
   
      A topology descriptor SHALL NOT include a combination of associations
      between two terminations (Ti,Tj) with and without the optional
      StreamID field, to avoid undefined behavior. For example (T1,T2,
      bothway) and (T1,T2,isolate,S1) shall not appear in the same
      descriptor. Upon receipt of such a topology descriptor, a MG shall
      respond with an error response, including Error 421 - "Unknown action
      or illegal combination of actions".
   
      Figure 7, and the table following it and Figure 8 following it show
      some examples of the effect of including topology descriptors in
      actions. In these examples it is assumed that the topology
      descriptors are applied in sequence.
   
         +------------------+  +------------------+  +------------------+
         |      +----+      |  |      +----+      |  |      +----+      |
         |      | T2 |      |  |      | T2 |      |  |      | T2 |      |
         |      +----+      |  |      +----+      |  |      +----+      |
         |       ^  ^       |  |          ^       |  |          ^       |
         |       |  |       |  |          |       |  |          |       |
         |    +--+  +--+    |  |          +---+   |  |          +--+    |
         |    |        |    |  |              |   |  |             |    |
         |    v        v    |  |              v   |  |             |    |
         | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
         | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |
         | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
         +------------------+  +------------------+  +------------------+
         1. No Topology Desc.   2. T1, T2, Isolate    3. T3, T2, Oneway
   
         +------------------+  +------------------+  +------------------+
         |      +----+      |  |      +----+      |  |      +----+      |
         |      | T2 |      |  |      | T2 |      |  |      | T2 |      |
         |      +----+      |  |      +----+      |  |      +----+      |
         |          |       |  |          ^       |  |       ^  ^       |
         |          |       |  |          |       |  |       |  |       |
         |          +--+    |  |          +---+   |  |    +--+  +--+    |
         |             |    |  |              |   |  |    |        |    |
         |             v    |  |              v   |  |    v        v    |
         | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
         | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |
         | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
         +------------------+  +------------------+  +------------------+
         4. T2, T3 oneway      5. T2, T3 bothway     6. T1, T2 bothway
   
   
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                          Figure 7: Example topologies
        Note: the direction of the arrow indicates the direction of flow
   
   
       Topology Description
   
       1        No topology descriptors
   
                 When no topology descriptors are included, all
                 Terminations have a bothway connection to all other
                 Terminations.
   
       2        T1, T2 Isolate
   
                 Removes the connection between T1 and T2. T3 has a
                 bothway connection with both T1 and T2. T1 and T2
                 have bothway connection to T3.
   
       3        T3, T2 oneway
   
                 A oneway connection from T3 to T2 (i.e. T2 receives
                 media flow from T3). A bothway connection between T1
                 and T3.
   
       4        T2, T3 oneway
   
                 A oneway connection between T2 to T3. T1 and T3
                 remain bothway connected
   
       5        T2, T3 bothway
   
                 T2 is bothway connected to T3. This results in the
                 same as 2.
   
       6        T1, T2 bothway (T2, T3 bothway and T1, T3 bothway
                 may be implied or explicit). All Terminations have a
                 bothway connection to all other Terminations.
   
   
                 +----+             +----+                 +----+
                 | T2 |             | T2 |                 | T2 |
                 +----+             +----+                 +----+
                  //\\               //\\                   //\\
                 //  \\             //  \\                 //  \\
               1//2  1\\2         1//2  1\\2             1//2  1\\2
              +---+   +---+      +---+   +---+          +---+   +---+
              |   | 1 |   |      |   | 1 |   |          |   | 1 |   |
   
   
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              |   |<->|   |      |   |<->|   |          |   |<--|   |
              |T1 |   |T3 |      |T1 |   |T3 |          |T1 |   |T3 |
              |   | 2 |   |      |   | 2 |   |          |   | 2 |   |
              |   |<->|   |      |   |-->|   |          |   |-->|   |
              |   |   |   |      |   |   |   |          |   |   |   |
              +---+   +---+      +---+   +---+          +---+   +---+
   
         1. No Topology Desc.  2. T1,T3, oneway,2      3. T3, T1,oneway,1
   
                   Figure 8: Example Topology at stream level
   
   
   
      A oneway connection must be implemented in such a way that the other
      Terminations in the Context are not aware of the change in topology.
   
   7.1.19   Error Descriptor
   
      If a responder encounters an error when processing a transaction
      request, it must include an error descriptor in its response.  A
      Notify request may contain an error descriptor as well.
   
      An error descriptor consists of an IANA-registered error code,
      optionally accompanied by an error text.  H.248.8 contains a list of
      valid error codes and error descriptions.
   
      An error descriptor shall be specified at the "deepest level" that is
      semantically appropriate for the error being described and that is
      possible given any parsing problems with the original request. An
      error descriptor may refer to a syntactical construct other than
      where it appears. For example, Error 422 - "Syntax Error in Action",
      could appear within a command even though it refers to the larger
      construct - the action - and not the particular command within which
      it appears.
   
   
   7.2   Command Application Programming Interface
   
      Following is an Application Programming Interface (API) describing
      the Commands of the protocol. This API is shown to illustrate the
      Commands and their parameters and is not intended to specify
      implementation (e.g. via use of blocking function calls). It
      describes the input parameters in parentheses after the command name
      and the return values in front of the Command. This is only for
      descriptive purposes; the actual Command syntax and encoding are
      specified in later subclauses. The order of parameters to commands is
      not fixed. Descriptors may appear as parameters to commands in any
      order. The descriptors SHALL be processed in the order in which they
      appear.
   
   
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      Any reply to a command may contain an error descriptor; the API does
      not specifically show this.
   
      All parameters enclosed by square brackets ([. . .]) are considered
      optional.
   
   7.2.1 Add
   
      The Add Command adds a Termination to a Context.
   
      TerminationID
      [,MediaDescriptor]
      [,ModemDescriptor] (*)
      [,MuxDescriptor]
      [,EventsDescriptor]
      [,SignalsDescriptor]
      [,DigitMapDescriptor]
      [,ObservedEventsDescriptor]
      [,EventBufferDescriptor]
      [,StatisticsDescriptor]
      [,PackagesDescriptor]
         Add( TerminationID
            [, MediaDescriptor]
            [, ModemDescriptor] (*)
            [, MuxDescriptor]
            [, EventsDescriptor]
            [, EventBufferDescriptor]
            [, SignalsDescriptor]
            [, DigitMapDescriptor]
            [, AuditDescriptor]
         )
   
      (*) ModemDescriptor has been deprecated in H.248.1 (05/2002).
   
      The TerminationID specifies the Termination to be added to the
      Context. The Termination is either created, or taken from the null
      Context. If a CHOOSE wildcard is used in the TerminationID, the
      selected  TerminationID will be returned. Wildcards may be used in an
      Add, but such usage would be unusual. If the wildcard matches more
      than one TerminationID, all possible matches are attempted, with
      results reported for each one. The order of attempts when multiple
      TerminationIDs match is not specified.
   
      The optional MediaDescriptor describes all media streams.
   
      The optional MuxDescriptor specifies a multiplexer if applicable. For
      convenience, if a Multiplex descriptor is present in an Add command
      and lists any Terminations that are not currently in the Context,
      such Terminations are added to the Context as if individual Add
   
   
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      commands listing the Terminations were invoked. If an error occurs on
      such an implied Add, error 471 - Implied Add for Multiplex failure
      shall be returned and further processing of the command shall cease.
   
      The EventsDescriptor parameter is optional. If present, it provides
      the list of events that SHOULD be detected on the Termination.
   
      The EventBufferDescriptor parameter is optional.  If present, it
      provides the list of events that the MG is requested to detect and
      buffer when EventBufferControl equals LockStep.
   
      The SignalsDescriptor parameter is optional. If present, it provides
      the list of signals that SHOULD be applied to the Termination.
   
      The DigitMapDescriptor parameter is optional. If present, it defines
      a DigitMap definition that may be used in an EventsDescriptor.
   
      The AuditDescriptor is optional. If present, the command will return
      descriptors as specified in the AuditDescriptor.
   
      All descriptors that can be modified could be returned by MG if a
      parameter was underspecified or overspecified. ObservedEvents,
      Statistics, and Packages, and the EventBuffer descriptors are
      returned only if requested in the AuditDescriptor.
   
      Add SHALL NOT be used on a Termination with a serviceState of
      "OutofService".
   
   7.2.2 Modify
   
      The Modify Command modifies the properties of a Termination.
   
      TerminationID
      [,MediaDescriptor]
      [,ModemDescriptor] (*)
      [,MuxDescriptor]
      [,EventsDescriptor]
      [,SignalsDescriptor]
      [,DigitMapDescriptor]
      [,ObservedEventsDescriptor]
      [,EventBufferDescriptor]
      [,StatisticsDescriptor]
      [,PackagesDescriptor]
         Modify( TerminationID
            [, MediaDescriptor]
            [, ModemDescriptor] (*)
            [, MuxDescriptor]
            [, EventsDescriptor]
            [, EventBufferDescriptor]
   
   
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            [, SignalsDescriptor]
            [, DigitMapDescriptor]
            [, AuditDescriptor]
         )
   
      (*) ModemDescriptor has been deprecated in H.248.1 (05/2002).
   
   
   
      The TerminationID may be specific if a single Termination in the
      Context is to be modified. Use of wildcards in the TerminationID may
      be appropriate for some operations. If the wildcard matches more than
      one TerminationID, all possible matches are attempted, with results
      reported for each one. The order of attempts when multiple
      TerminationIDs match is not specified. The CHOOSE option is an error,
      as the Modify command may only be used on existing Terminations.
   
      For convenience, if a Multiplex Descriptor is present in a Modify
      command, then:
   
      -  if the new Multiplex Descriptor lists any Terminations that are
         not currently in the Context, such Terminations are added to the
         context as if individual Add commands listing the Terminations
         were invoked.
   
      -  if any Terminations listed previously in the Multiplex Descriptor
         are no longer present in the new Multiplex Descriptor, they are
         subtracted from the context as if individual Subtract commands
         listing the Terminations were invoked.
   
      The remaining parameters to Modify are the same as those to Add.
      Possible return values are the same as those to Add.
   
   7.2.3 Subtract
   
      The Subtract Command disconnects a Termination from its Context and
      returns statistics on the Termination's participation in the Context.
   
      TerminationID
      [,MediaDescriptor]
      [,ModemDescriptor] (*)
      [,MuxDescriptor]
      [,EventsDescriptor]
      [,SignalsDescriptor]
      [,DigitMapDescriptor]
      [,ObservedEventsDescriptor]
      [,EventBufferDescriptor]
      [,StatisticsDescriptor]
      [,PackagesDescriptor]
   
   
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         Subtract(TerminationID
            [, AuditDescriptor]
         )
   
      (*) ModemDescriptor has been deprecated in H.248.1 (05/2002).
   
      TerminationID in the input parameters represents the Termination that
      is being subtracted. The TerminationID may be specific or may be a
      wildcard value indicating that all (or a set of related) Terminations
      in the Context of the Subtract Command are to be subtracted. If the
      wildcard matches more than one TerminationID, all possible matches
      are attempted, with results reported for each one. The order of
      attempts when multiple TerminationIDs match is not specified.
   
      The use of CHOOSE in the TerminationID is an error, as the Subtract
      command may only be used on existing Terminations.
   
      ALL may be used as the ContextID as well as the TerminationId in a
      Subtract, which would have the effect of deleting all Contexts,
      deleting all ephemeral Terminations, and returning all physical
      Terminations to Null Context. Subtract of a termination from the Null
      Context is not allowed.
   
      For convenience, if a multiplexing Termination is the object of a
      Subtract command, then any bearer Terminations listed in its
      Multiplex Descriptor are subtracted from the context as if individual
      Subtract commands listing the Terminations were invoked.
   
      By default, the Statistics parameter is returned to report
      information collected on the Termination or Terminations specified in
      the Command. The information reported applies to the Termination's or
      Terminations' existence in the Context from which it or they are
      being subtracted.
   
      The AuditDescriptor is optional. If present, the command will return
      only those descriptors as specified in the AuditDescriptor, which may
      be empty. If omitted, the Statistics descriptor is returned, by
      default. Possible return values are the same as those to Add.
   
      When a provisioned Termination is Subtracted from a Context, its
      property values shall revert to:
   
      -  the default value, if specified for the property and not
         overridden by provisioning;
   
      -  otherwise, the provisioned value.
   
   
   
   
   
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   7.2.4 Move
   
      The Move Command moves a Termination to another Context from its
      current Context in one atomic operation. The Move command is the only
      command that refers to a Termination in a Context different from that
      to which the command is applied. The Move command shall not be used
      to move Terminations to or from the null Context.
   
      TerminationID
      [,MediaDescriptor]
      [,ModemDescriptor] (*)
      [,MuxDescriptor]
      [,EventsDescriptor]
      [,SignalsDescriptor]
      [,DigitMapDescriptor]
      [,ObservedEventsDescriptor]
      [,EventBufferDescriptor]
      [,StatisticsDescriptor]
      [,PackagesDescriptor]
         Move( TerminationID
            [, MediaDescriptor]
            [, ModemDescriptor] (*)
            [, MuxDescriptor]
            [, EventsDescriptor]
            [, EventBufferDescriptor]
            [, SignalsDescriptor]
            [, DigitMapDescriptor]
            [, AuditDescriptor]
         )
   
      (*) ModemDescriptor has been deprecated in H.248.1 (05/2002).
   
      The TerminationID specifies the Termination to be moved. It may be
      wildcarded, but CHOOSE shall not be used in the TerminationID. If the
      wildcard matches more than one TerminationID, all possible matches
      are attempted, with results reported for each one. The order of
      attempts when multiple TerminationIDs match is not specified. The
      Context to which the Termination is moved is indicated by the target
      ContextId in the Action. If the last remaining Termination is moved
      out of a Context, the Context is deleted.
   
      The Move command does not affect the properties of the Termination on
      which it operates, except those properties explicitly modified by
      descriptors included in the Move command. The AuditDescriptor with
      the Statistics option, for example, would return statistics on the
      Termination just prior to the Move. Possible descriptors returned
      from Move are the same as for Add.
   
   
   
   
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      For convenience, if a multiplexing Termination is the object of a
      Move command, then any bearer Terminations listed in its Multiplex
      Descriptor are also moved as if individual Move commands listing the
      Terminations were invoked.
   
      Move SHALL NOT be used on a Termination with a serviceState of
      "OutofService".
   
   7.2.5 AuditValue
   
      The AuditValue Command returns the current values of properties,
      events, signals and statistics associated with Terminations. An
      AuditValue may request the contents of a descriptor or of a single
      property, event, signal or statistics.
   
      TerminationID
      [,MediaDescriptor]
      [,ModemDescriptor] (*)
      [,MuxDescriptor]
      [,EventsDescriptor]
      [,SignalsDescriptor]
      [,DigitMapDescriptor]
      [,ObservedEventsDescriptor]
      [,EventBufferDescriptor]
      [,StatisticsDescriptor]
      [,PackagesDescriptor]
         AuditValue(TerminationID,
            AuditDescriptor
         )
   
      (*) ModemDescriptor has been deprecated in H.248.1 (05/2002).
   
      TerminationID may be specific or wildcarded. If the wildcard matches
      more than one TerminationID, all possible matches are attempted, with
      results reported for each one. The order of attempts when multiple
      TerminationIDs match is not specified. If a wildcarded response is
      requested, only one command return is generated, with the contents
      containing the union of the values of all Terminations matching the
      wildcard. This convention may reduce the volume of data required to
      audit a group of Terminations. Use of CHOOSE is an error.
   
      Descriptors or individual properties, signals, events and statistics
      can be audited.
   
      -  An audit of a descriptor may be requested by identifying the
         desired descriptor in the AuditDescriptor with no further
         information.
   
   
   
   
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      -  To audit an individual property in the media descriptor the
         relevant stream ID (optional), group ID (optional) and propertyID
         are included. The current value of the property is returned. Group
         ID is used in the case where the local control Reserve Group flag
         is used. Group ID 1 corresponds to the first group (session
         decription) reserved, Group ID 2 the next group etcetera.
   
      -  To audit a signal the relevant signal list ID and/or signal ID are
         provided. Only if the signal is active the values of all the
         signal parameters are returned including: the keepactive
         indication, signal type, duration, signal completion indication
         and package defined properties.
   
      -  To audit an event, the relevant stream id (optional), eventID,
         requestID (optional) are provided. The values of all the event
         parameters are returned including: event actions and packaged
         defined parameters.
   
      -  To audit a statistic the identity of the statistic is provided.
         The current value of the statistic is returned. The statistic is
         not reset.
   
      -  To audit a package the identity and version of the package is
         provided. All properties, signals, events and statistics defined
         in that particular package are returned with their current value.
   
      It is possible to audit multiple individual items in one request.
   
      If a descriptor audit is requested, the appropriate descriptors, with
      the current values for the Termination, are returned from AuditValue.
      Values appearing in multiple instances of a descriptor are defined to
      be alternate values supported, with each parameter in a descriptor
      considered independent.
   
      ObservedEvents returns a list of events in the EventBuffer. If the
      ObservedEventsDescriptor is audited while a DigitMap is active, the
      returned ObservedEvents descriptor also includes a digit map
      completion event that shows the current dial string but does not show
      a Termination method.
   
      EventBuffer returns the set of events and associated parameter values
      currently enabled in the EventBufferDescriptor. PackagesDescriptor
      returns a list of packages realized by the Termination.
      DigitMapDescriptor returns the name or value of the current DigitMap
      for the Termination. DigitMap requested in an AuditValue command with
      TerminationID ALL returns all DigitMaps in the gateway. Statistics
      returns the current values of all statistics being kept on the
      Termination. Specifying an empty Audit descriptor results in only the
      TerminationID being returned. This may be useful to get a list of
   
   
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      TerminationIDs when used with wildcard. Annexes A and B provide a
      special syntax for presenting such a list in condensed form, such
      that the AuditValue command tag does not have to be repeated for each
      TerminationID.
   
      AuditValue results depend on the Context, viz. specific, null, or
      wildcarded. (Note that ContextID All does not include the null
      Context.) The TerminationID may be specific, or wildcarded.
   
      The following are examples of what is returned in case the context
      and/or the termination is wildcarded and a wildcarded response has
      been specified.
   
      Assume that the gateway has 4 terminations: t1/1, t1/2, t2/1 and
      t2/2. Assume that terminations t1/* have implemented packages aaa and
      bbb and that terminations t2/* have implemented packages ccc and ddd.
      Assume that Context 1 has t1/1 and t2/1 in it and that Context 2 has
      t1/2 and t2/2 in it.
   
      The command:
   
         Context=1{AuditValue=t1/1{Audit{Packages}}}
   
      Returns:
   
         Context=1{AuditValue=t1/1{Packages{aaa,bbb}}}
   
      The command:
   
         Context=*{AuditValue=t2/*{Audit{Packages}}}
   
      Returns:
   
         Context=1{AuditValue=t2/1{Packages{ccc,ddd}}},
         Context=2{AuditValue=t2/2{Packages{ccc,ddd}}}
   
      The command:
   
         Context=*{W-AuditValue=t1/*{Audit{Packages}}}
   
      Returns:
   
         Context=*{W-AuditValue=t1/*{Packages{aaa,bbb}}}
   
      Note: A wildcard response may also be used for other commands such as
      Subtract.
   
      The following illustrates other information that can be obtained with
      the AuditValue Command:
   
   
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      ContextID   TerminationID   Information Obtained
   
      Specific    wildcard        Audit of matching Terminations in a
                                   Context
   
      Specific    specific        Audit of a single Termination in a
                                   Context
   
      Null        Root            Audit of Media Gateway state and
                                   events
   
      Null        wildcard        Audit of all matching Terminations
                                   in the null Context
   
      Null        specific        Audit of a single Termination
                                   outside of any Context
   
      All         wildcard        Audit of all matching Terminations
                                   and the Context to which they are
                                   associated
   
      All         Root            List of all ContextIds (the
                                   ContextID list SHOULD be returned by
                                   using multiple action replies, each
                                   containing a ContextID from the
                                   list)
   
      All         Specific        (Non-null) ContextID in which the
                                   Termination currently exists
   
   
   
   7.2.6 AuditCapabilities
   
      The AuditCapabilities Command returns the possible values of
      properties, events, signals and statistics associated with
      Terminations. An AuditCapabilities may be requested for the contents
      of a descriptor or for a single property, event, signal or
      statistics.
   
      TerminationID
      [,MediaDescriptor]
      [,ModemDescriptor](*)
      [,MuxDescriptor]
      [,EventsDescriptor]
      [,SignalsDescriptor]
      [,ObservedEventsDescriptor]
      [,EventBufferDescriptor]
   
   
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      [,StatisticsDescriptor]
         AuditCapabilities(
            TerminationID,
            AuditDescriptor
         )
   
      (*) ModemDescriptor has been deprecated in H.248.1 (02/2002).
   
      Descriptors or individual properties, signals, events and statistics
      can be audited.
   
      -  An audit of a entire descriptor may be requested by identifying
         the desired descriptor in the AuditDescriptor with no further
         information.
   
      -  To audit an individual property in the media descriptor the
         relevant stream ID (optional) and propertyID are included. A list
         of possible values of the property are returned.
   
      -  To audit a signal the relevant signal list ID and/or signal ID are
         provided. A list of possible values associated with each signal
         parameter is returned (including: the keepactive indication,
         signal type, duration, signal completion indication and package
         defined properties).
   
      -  To audit an event the relevant stream id (optional), eventID,
         requestID (optional) are provided. A list of possible values
         associated with each event parameter is returned (including: event
         actions and packaged defined parameters).
   
      -  To audit a statistic the identity of statistic is provided. The
         possible values of the statistic are returned. The statistic is
         not reset.
   
      If a descriptor audit is requested the appropriate descriptors, with
      the possible values for the Termination, are returned from
      AuditCapabilities. Descriptors may be repeated where there are
      multiple possible values.
   
      If a wildcarded response is requested, only one command return is
      generated, with the contents containing the union of the values of
      all Terminations matching the wildcard. This convention may reduce
      the volume of data required to audit a group of Terminations.
   
      If a property, signal, event or statistic is audited, the appropriate
      properties, signals events, and statistics with the capabilities of
      the Termination are returned from AuditCapabilities.
   
   
   
   
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      Interpretation of what capabilities are requested for various values
      of ContextID and TerminationID is the same as in AuditValue.
   
      The EventsDescriptor returns the list of possible events on the
      Termination together with the list of all possible values for the
      EventsDescriptor Parameters. EventBufferDescriptor returns the same
      information as EventsDescriptor. The SignalsDescriptor returns the
      list of possible signals that could be applied to the Termination
      together with the list of all possible values for the Signals
      Parameters. StatisticsDescriptor returns the names of the statistics
      being kept on the termination. ObservedEventsDescriptor returns the
      names of active events on the Termination. DigitMap and Packages are
      not legal in AuditCapability.
   
      The following illustrates other information that can be obtained with
      the AuditCapabilties Command:
   
      ContextID  TerminationID   Information Obtained
   
      Specific   wildcard        Audit of matching Terminations in
                                 a Context
   
      Specific   specific        Audit of a single Termination in a
                                 Context
   
      Null       Root            Audit of MG state and events
   
      Null       wildcard        Audit of all matching Terminations
                                 in the Null Context
   
      Null       specific        Audit of a single Termination
                                 outside of any Context
   
      All        wildcard        Audit of all matching Terminations
                                 and the Context to which they are
                                 associated
   
      All        Root            Same as for AuditValue
   
      All        Specific        Same as for AuditValue
   
   
   
   7.2.7 Notify
   
      The Notify Command allows the Media Gateway to notify the Media
      Gateway Controller of events occurring within the Media Gateway.
   
   
   
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      TerminationID
         Notify(TerminationID,
            ObservedEventsDescriptor,
            [ErrorDescriptor]
         )
   
      The TerminationID parameter specifies the Termination issuing the
      Notify Command. The TerminationID shall be a fully qualified name.
   
      The ObservedEventsDescriptor contains the RequestID and a list of
      events that the Media Gateway detected in the order that they were
      detected. Each event in the list is accompanied by parameters
      associated with the event and optionally an indication of the time
      that the event was detected. Procedures for sending Notify commands
      with RequestID equal to 0 are for further study.
   
      Notify Commands with RequestID not equal to 0 shall occur only as the
      result of detection of an event specified by an Events descriptor
      which is active on the Termination concerned.
   
      The RequestID returns the RequestID parameter of the EventsDescriptor
      that triggered the Notify Command. It is used to correlate the
      notification with the request that triggered it. The events in the
      list must have been requested via the triggering EventsDescriptor or
      embedded events descriptor unless the RequestID is 0 (which is for
      further study).
   
      The ErrorDescriptor may be sent in the Notify Command as a result of
      Error 518 - "Event buffer full".
   
   7.2.8 ServiceChange
   
      The ServiceChange Command allows the Media Gateway to notify the
      Media Gateway Controller that a Termination or group of Terminations
      is about to be taken out of service or has just been returned to
      service. The Media Gateway Controller may indicate that
      Termination(s) shall be taken out of or returned to service. The
      Media Gateway may notify the MGC that the capability of a Termination
      has changed. It also allows a MGC to hand over control of a MG to
      another MGC.
   
      TerminationID,
      [ServiceChangeDescriptor]
         ServiceChange(TerminationID,
            ServiceChangeDescriptor
         )
   
      The TerminationID parameter specifies the Termination(s) that are
      taken out of or returned to service. Wildcarding of Termination names
   
   
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      is permitted, with the exception that the CHOOSE mechanism shall not
      be used. Use of the "Root" TerminationID indicates a ServiceChange
      affecting the entire Media Gateway.
   
      The ServiceChangeDescriptor contains the following parameters as
      required:
   
      -  ServiceChangeMethod
      -  ServiceChangeReason
      -  ServiceChangeDelay
      -  ServiceChangeAddress
      -  ServiceChangeProfile
      -  ServiceChangeVersion
      -  ServiceChangeMgcId
      -  TimeStamp
      -  ServiceChangeInfo
   
      The ServiceChangeMethod parameter specifies the type of ServiceChange
      that will or has occurred:
   
      1) Graceful - indicates that the specified Terminations will be taken
         out of service after the specified ServiceChangeDelay; established
         connections are not yet affected, but the Media Gateway Controller
         SHOULD refrain from establishing new connections and SHOULD
         attempt to gracefully tear down existing connections on the
         Termination(s) affected by the serviceChange command. The MG
         SHOULD set Termination serviceState at the expiry of
         ServiceChangeDelay or the removal of the Termination from an
         active Context (whichever is first), to "out of service".
   
      2) Forced - indicates that the specified Terminations were taken
         abruptly out of service and any established connections associated
         with them may be lost. For non-Root terminations, the MGC is
         responsible for cleaning up the Context (if any) with which the
         failed Termination is associated. At a minimum the Termination
         shall be subtracted from the Context. The Termination serviceState
         SHOULD be "out of service". For the root termination, the MGC can
         assume that all connections are lost on the MG and thus can
         consider that all the terminations have been subtracted.
   
      3) Restart - indicates that service will be restored on the specified
         Terminations after expiration of the ServiceChangeDelay. The
         serviceState SHOULD be set to "inService" upon expiry of
         ServiceChangeDelay.
   
      4) Disconnected - always applied with the Root TerminationID,
         indicates that the MG lost communication with the MGC, but it was
         subsequently restored to the same MGC (possibly after trying other
         MGCs on a pre-provisioned list). Since MG state may have changed,
   
   
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         the MGC may wish to use the Audit command to resynchronize its
         state with the MG's.
   
      5) Handoff - sent from the MGC to the MG, this reason indicates that
         the MGC is going out of service and a new MGC association must be
         established. Sent from the MG to the MGC, this indicates that the
         MG is attempting to establish a new association in accordance with
         a Handoff received from the MGC with which it was previously
         associated.
   
      6) Failover - sent from MG to MGC to indicate the primary MG is out
         of service and a secondary MG is taking over. This serviceChange
         method is also sent from the MG to the MGC when the MG detects
         that MGC has failed.
   
      7) Another value whose meaning is mutually understood between the MG
         and the MGC.
   
      The ServiceChangeReason parameter specifies the reason why the
      ServiceChange has or will occur. It consists of an alphanumeric token
      (IANA registered) and, optionally, an explanatory string.
   
      The optional ServiceChangeAddress parameter specifies the address
      (e.g. IP port number for IP networks) to be used for subsequent
      communications. It can be specified in the input parameter descriptor
      or the returned result descriptor. ServiceChangeAddress and
      ServiceChangeMgcId parameters must not both be present in the
      ServiceChangeDescriptor or the ServiceChangeResultDescriptor. The
      ServiceChangeAddress provides an address to be used within the
      Context of the association currently being negotiated, while the
      ServiceChangeMgcId provides an alternate address where the MG SHOULD
      seek to establish another association. Note that the use of
      ServiceChangeAddress is not encouraged.  MGCs and MGs must be able to
      cope with the ServiceChangeAddress being either a full address or
      just a port number in the case of TCP transports.
   
      The optional ServiceChangeDelay parameter is expressed in seconds. If
      the delay is absent or set to zero, the delay value SHOULD be
      considered to be null. In the case of a "graceful"
      ServiceChangeMethod, a null delay indicates that the Media Gateway
      Controller SHOULD wait for the natural removal of existing
      connections and SHOULD not establish new connections. For "graceful"
      only, a null delay means the MG must not set serviceState "out of
      service" until the Termination is in the null Context.
   
      The optional ServiceChangeProfile parameter specifies the Profile (if
      any) of the protocol supported. The ServiceChangeProfile includes the
      version of the profile supported.
   
   
   
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      The optional ServiceChangeVersion parameter contains the protocol
      version and is used if protocol version negotiation occurs (see
      11.3).
   
      The optional TimeStamp parameter specifies the actual time as kept by
      the sender. As such, it is not necessarily absolute time according
      to, for example, a local time zone - it merely establishes an
      arbitrary starting time against which all future timestamps
      transmitted by a sender during this association shall be compared. It
      can be used by the responder to determine how its notion of time
      differs from that of its correspondent. TimeStamp is sent with a
      precision of hundredths of a second.
   
      The optional Extension parameter may contain any value whose meaning
      is mutually understood by the MG and MGC.
   
      The optional ServiceChangeInfo parameter may contain the
      package/property/signal/event/statistic of the reason that caused the
      service change.
   
      A ServiceChange Command specifying the "Root" for the TerminationID
      and ServiceChangeMethod equal to Restart is a registration command by
      which a Media Gateway announces its existence to the Media Gateway
      Controller. The Media Gateway may also register by specifying the
      "Root" for the TerminationID and ServiceChangeMethod equal to
      Failover when the MG detects MGC failures. The Media Gateway is
      expected to be provisioned with the name of one primary and
      optionally some number of alternate Media Gateway Controllers.
      Acknowledgement of the ServiceChange Command completes the
      registration process, except when the MGC has returned an alternative
      ServiceChangeMgcId as described in the following paragraph. The MG
      may specify the transport ServiceChangeAddress to be used by the MGC
      for sending messages in the ServiceChangeAddress parameter in the
      input ServiceChangeDescriptor. The MG may specify an address in the
      ServiceChangeAddress parameter of the ServiceChange request, and the
      MGC may also do so in the ServiceChange reply. In either case, the
      recipient must use the supplied address as the destination for all
      subsequent transaction requests within the association. At the same
      time, as indicated in clause 9, transaction replies and pending
      indications must be sent to the address from which the corresponding
      requests originated. This must be done even if it implies extra
      messaging because commands and responses cannot be packed together.
      The TimeStamp parameter shall be sent with a registration command and
      its response.
   
      The Media Gateway Controller may return a ServiceChangeMgcId
      parameter that describes the Media Gateway Controller that SHOULD
      preferably be contacted for further service by the Media Gateway. In
      this case the Media Gateway shall reissue the ServiceChange command
   
   
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      to the new Media Gateway Controller. The MGC specified in a
      ServiceChangeMgcId, if provided, shall be contacted before any
      further alternate MGCs. On a HandOff message from MGC to MG, the
      ServiceChangeMgcId is the new MGC that will take over from the
      current MGC.
   
      The return from ServiceChange is empty except when the Root
      terminationID is used. In that case it includes the following
      parameters as required:
   
      -  ServiceChangeAddress, if the responding MGC wishes to specify a
         new destination for messages from the MG for the remainder of the
         association;
   
      -  ServiceChangeMgcId, if the responding MGC does not wish to sustain
         an association with the MG;
   
      -  ServiceChangeProfile, if the responder wishes to negotiate the
         profile to be used for the association. The profile (name and
         version) is only returned in reply in the case that the MGC cannot
         support the specified profiles in the ServiceChangeRequest. The
         returned reply shall indicate the profile and version supported or
         "NoProfile" if no profile is supported. Upon reception of a
         profile in the reply the MG may continue the relationship with the
         current MGC or contact secondary MGCs and establish a relationship
         with them. If the profile is not returned the MGC will use the
         capabilities specified by the Profile indicated in the service
         change request;
   
      -  ServiceChangeVersion, if the responder wishes to negotiate the
         version of the protocol to be used for the association.
   
      The following ServiceChangeReasons are defined. This list may be
      extended by an IANA registration as outlined in 14.3.
   
         900 Service Restored
         901 Cold Boot
         902 Warm Boot
         903 MGC Directed Change
         904 Termination malfunctioning
         905 Termination taken out of service
         906 Loss of lower layer connectivity (e.g. downstream sync)
         907 Transmission Failure
         908 MG Impending Failure
         909 MGC Impending Failure
         910 Media Capability Failure
         911 Modem Capability Failure
         912 Mux Capability Failure
         913 Signal Capability Failure
   
   
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         914 Event Capability Failure
         915 State Loss
         916 Packages Change
         917 Capability Change
   
   
   
   7.2.9 Manipulating and Auditing Context Attributes
   
      The commands of the protocol as discussed in the preceding subclauses
      apply to Terminations. This subclause specifies the processing of
      Context attributes.
   
      An action may contain instructions for the manipulation and auditing
      of Context properties (see clause 8).
   
      The MGC may audit a specific Context to determine the current value
      of individual context properties.  The MGC may determine the current
      values for all existing (non-NULL) Contexts by specifying ContextID
      ALL in the Audit request. If context attributes are added or have
      been modified by the same action as the Audit request the value/s
      returned shall be after the action has been applied.
   
      The following illustrates information that can be obtained with a
      context Audit:
   
       ContextID TerminationID   Audit
   
       Specific  Not Applicable  Context attribute's value in the
                                   specified context.
   
       Null      Not Applicable  Not Allowed
   
       All       Not Applicable  Current values for all existing
                                   (non-NULL) Contexts by specifying
                                   ContextID ALL in the Audit request.
   
                                   A response for ContextID ALL is
                                   presented through an actionReply
                                   per context.
   
   
   
      An action may also include a request to change the attributes of a
      Context.
   
      The Context properties that may be included in an action reply are
      used to return information to a MGC. This can be information
   
   
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      requested by an audit of Context attributes or details of the effect
      of manipulation of a Context.
   
      If a MG receives an action which contains both a request to audit
      context attributes and a request to manipulate those attributes, the
      response SHALL include the values of the attributes after processing
      the manipulation request.
   
   7.2.10   Generic Command Syntax
   
      The protocol can be encoded in a binary format or in a text format.
      MGCs SHOULD support both encoding formats. MGs may support both
      formats.
   
      The protocol syntax for the binary format of the protocol is defined
      in Annex A. Annex C specifies the encoding of the Local and Remote
      descriptors for use with the binary format.
   
      A complete ABNF of the text encoding of the protocol per RFC 2234 is
      given in Annex B. SDP is used as the encoding of the Local and Remote
      descriptors for use with the text encoding as modified in 7.1.8.
   
   
   8  TRANSACTIONS
   
      Commands between the Media Gateway Controller and the Media Gateway
      are grouped into Transactions, each of which is identified by a
      TransactionID. Transactions consist of one or more Actions. An Action
      consists of a non-empty series of Commands, Context property
      modifications, or Context property audits that are limited to
      operating within a single Context. Consequently, each Action
      typically specifies a ContextID. However, there are two circumstances
      where a specific ContextID is not provided with an Action. One is the
      case of modification of a Termination outside of a Context. The other
      is where the controller requests the gateway to create a new Context.
      Figure 9 is a graphic representation of the Transaction, Action and
      Command relationships.
   
         +----------------------------------------------------------+
         | Transaction x                                            |
         |  +----------------------------------------------------+  |
         |  | Action 1                                           |  |
         |  | +---------+  +---------+  +---------+  +---------+ |  |
         |  | | Command |  | Command |  | Command |  | Command | |  |
         |  | |    1    |  |    2    |  |    3    |  |    4    | |  |
         |  | +---------+  +---------+  +---------+  +---------+ |  |
         |  +----------------------------------------------------+  |
         |                                                          |
   
   
   
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         |  +----------------------------------------------------+  |
         |  | Action 2                                           |  |
         |  | +---------+                                        |  |
         |  | | Command |                                        |  |
         |  | |    1    |                                        |  |
         |  | +---------+                                        |  |
         |  +----------------------------------------------------+  |
         |                                                          |
         |  +----------------------------------------------------+  |
         |  | Action 3                                           |  |
         |  | +---------+  +---------+  +---------+              |  |
         |  | | Command |  | Command |  | Command |              |  |
         |  | |    1    |  |    2    |  |    3    |              |  |
         |  | +---------+  +---------+  +---------+              |  |
         |  +----------------------------------------------------+  |
         +----------------------------------------------------------+
   
                        Figure 9: Transactions, Actions and Commands
   
      Transactions are presented as TransactionRequests. Corresponding
      responses to a TransactionRequest are received in a single reply,
      possibly preceded by a number of TransactionPending messages (see
      8.2.3).
   
      Transactions guarantee ordered Command processing. That is, Commands
      within a Transaction are executed sequentially. Ordering of
      Transactions is NOT guaranteed - transactions may be executed in any
      order, or simultaneously.
   
      At the first failing Command in a Transaction, processing of the
      remaining Commands in that Transaction stops. If a command contains a
      wildcarded TerminationID, the command is attempted with each of the
      actual TerminationIDs matching the wildcard. A response within the
      TransactionReply is included for each matching TerminationID, even if
      one or more instances generated an error. If any TerminationID
      matching a wildcard results in an error when executed, any commands
      following the wildcarded command are not attempted.
   
      Commands may be marked as "Optional" which can override this
      behaviour - if a command marked as Optional results in an error,
      subsequent commands in the Transaction will be executed. If a command
      fails, the MG shall as far as possible restore the state that existed
      prior to the attempted execution of the command before continuing
      with command processing.
   
      A TransactionReply includes the results for all of the Commands in
      the corresponding TransactionRequest. The TransactionReply includes
      the return values for the Commands that were executed successfully,
      and the Command and error descriptor for any Command that failed.
   
   
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      TransactionPending is used to periodically notify the receiver that a
      Transaction has not completed yet, but is actively being processed.
   
      Applications SHOULD implement an application level timer per
      transaction. Expiration of the timer SHOULD cause a retransmission of
      the request. Receipt of a Reply SHOULD cancel the timer. Receipt of
      Pending SHOULD restart the timer.
   
   8.1   Common parameters
   
   8.1.1 Transaction Identifiers
   
      Transactions are identified by a TransactionID, which is assigned by
      sender and is unique within the scope of the sender. A response
      containing an error descriptor to indicate that the TransactionID is
      missing in a request shall use TransactionID 0 in the corresponding
      TransactionReply.
   
   8.1.2 Context Identifiers
   
      Contexts are identified by a ContextID, which is assigned by the
      Media Gateway and is unique within the scope of the Media Gateway.
      The Media Gateway Controller shall use the ContextID supplied by the
      Media Gateway in all subsequent Transactions relating to that
      Context. The protocol makes reference to a distinguished value that
      may be used by the Media Gateway Controller when referring to a
      Termination that is currently not associated with a Context, namely
      the null ContextID.
   
      The CHOOSE wildcard is used to request that the Media Gateway create
      a new Context.
   
      The MGC may use the ALL wildcard to address all Contexts on the MG.
      The null Context is not included when the ALL wildcard is used.
   
      The MGC shall not use partially specified ContextIDs containing the
      CHOOSE or ALL wildcards.
   
   8.2   Transaction Application Programming Interface
   
      Following is an Application Programming Interface (API) describing
      the Transactions of the protocol. This API is shown to illustrate the
      Transactions and their parameters and is not intended to specify
      implementation (e.g. via use of blocking function calls). It will
      describe the input parameters and return values expected to be used
      by the various Transactions of the protocol from a very high level.
      Transaction syntax and encodings are specified in later subclauses.
   
   
   
   
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   8.2.1 TransactionRequest
   
      The TransactionRequest is invoked by the sender. There is one
      Transaction per request invocation. A request contains one or more
      Actions, each of which specifies its target Context and one or more
      Commands per Context.
   
         TransactionRequest(TransactionId {
            ContextID {Command ... Command},
               . . .
            ContextID  {Command ... Command } })
   
      The TransactionID parameter must specify a value for later
      correlation with the TransactionReply or TransactionPending response
      from the receiver.
   
      The ContextID parameter must specify a value to pertain to all
      Commands that follow up to either the next specification of a
      ContextID parameter or the end of the TransactionRequest, whichever
      comes first.
   
      The Command parameter represents one of the Commands mentioned in 7.2
      (Command Application Programming Interface).
   
   8.2.2 TransactionReply
   
      The TransactionReply is invoked by the receiver. There is one reply
      invocation per transaction. A reply contains one or more Actions,
      each of which must specify its target Context and one or more
      Responses per Context. The TransactionReply is invoked by the
      responder when it has processed the TransactionRequest.
   
      A TransactionRequest has been processed:
   
      -  when all actions in that TransactionRequest have been processed;
         or
   
      -  when an error is encountered in processing that
         TransactionRequest, except when the error is in an optional
         command.
   
      A command has been processed when all descriptors in that command
      have been processed.
   
      A SignalsDescriptor is considered to have been processed when it has
      been established that the descriptor is syntactically valid, the
      requested signals are supported and they have been queued to be
      applied.
   
   
   
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      An EventsDescriptor or EventBufferDescriptor is considered to have
      been processed when it has been established that the descriptor is
      syntactically valid, the requested events can be observed, any
      embedded signals can be generated, any embedded events can be
      detected, and the MG has been brought into a state in which the
      events will be detected.
   
         TransactionReply(TransactionID {
            ContextID { Response ... Response },
               . . .
            ContextID { Response ... Response } })
   
      The TransactionID parameter must be the same as that of the
      corresponding TransactionRequest.
   
      The ContextID parameter must specify a value to pertain to all
      Responses for the action. The ContextID may be specific, all or null.
   
      Each of the Response parameters represents a return value as
      mentioned in 7.2, or an error descriptor if the command execution
      encountered an error. Commands after the point of failure are not
      processed and, therefore, Responses are not issued for them.
   
      An exception to this occurs if a command has been marked as optional
      in the Transaction request. If the optional command generates an
      error, the transaction still continues to execute, so the Reply
      would, in this case, have Responses after an Error.
   
      Section 7.1.19 Error Descriptor specifies the generation of error
      descriptors.  The text below discusses several individual cases.
   
      If the receiver encounters an error in processing a ContextID, the
      requested Action response will consist of the Context ID and a single
      error descriptor, 422 - "Syntax Error in Action".
   
      If the receiver encounters an error such that it cannot determine a
      legal Action, it will return a TransactionReply consisting of the
      TransactionID and a single error descriptor, 422 - "Syntax Error in
      Action". If the end of an action cannot be reliably determined but
      one or more commands can be parsed, it will process them and then
      send 422 - "Syntax Error in Action" as the last action for the
      transaction. If the receiver encounters an error such that is cannot
      determine a legal Transaction, it will return a TransactionReply with
      a null TransactionID and a single error descriptor (403 - "Syntax
      Error in Transaction").
   
      If the end of a transaction cannot be reliably determined and one or
      more Actions can be parsed, it will process them and then return 403
      - "Syntax Error in Transaction" as the last action reply for the
   
   
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      transaction. If no Actions can be parsed, it will return 403 -
      "Syntax Error in Transaction" as the only reply.
   
      If the terminationID cannot be reliably determined, it will send 442
      - "Syntax Error in Command" as the action reply.
   
      If the end of a command cannot be reliably determined, it will return
      442 - "Syntax Error in Command" as the reply to the last action it
      can parse.
   
   8.2.3 TransactionPending
   
      The receiver invokes the TransactionPending. A TransactionPending
      indicates that the Transaction is actively being processed, but has
      not been completed. It is used to prevent the sender from assuming
      the TransactionRequest was lost where the Transaction will take some
      time to complete.
   
         TransactionPending(TransactionID { } )
   
      The TransactionID parameter must be the same as that of the
      corresponding TransactionRequest. A property of root
      (normalMGExecutionTime) is settable by the MGC to indicate the
      interval within which the MGC expects a response to any transaction
      from the MG. Another property (normalMGCExecutionTime) is settable by
      the MGC to indicate the interval within which the MG SHOULD expect a
      response to any transaction from the MGC. Senders may receive more
      than one TransactionPending for a command. If a duplicate request is
      received when pending, the responder may send a duplicate pending
      immediately, or continue waiting for its timer to trigger another
      TransactionPending.
   
      A property of the root termination (MGOriginatedPendingLimit) is
      settable by the MGC to indicate the number of TransactionPendings
      that can be received from the MG. When the value expressed by this
      property is exceeded, the MG shall stop the transaction processing
      and send back a TransactionReply, otherwise the MGC can assume the
      Transaction to be in error.
   
      Another property of the root termination (MGCOriginatedPendingLimit)
      is settable by the MGC to indicate the number of TransactionPendings
      that can be received from the MGC. When the value expressed by this
      property is exceeded, the MGC shall stop the transaction processing
      and send back a TransactionReply otherwise the MG can assume the
      Transaction to be in error.
   
      The xxxOriginatedPendingLimit (MGOriginatedPendingLimit or
      MGCOriginatedPendingLimit) may be exceeded either because of long
      command processing or due to an error (e.g. a command caused a loop).
   
   
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      In both cases the receiver of the original TransactionRequest will
      issue a TransactionReply with an error descriptor as a response
      parameter in correspondence with either the offending long command or
      the command that caused the error. Further commands in the
      transaction shall not be processed. Error 506 - "Number of
      TransactionPendings Exceeded" shall be used.
   
      NOTE - To prevent a situation where the xxxOriginatedPendingLimit
      (MGOriginatedPendingLimit or MGCOriginatedPendingLimit) is exceeded
      due to an error and the receiver of the original TransactionRequest
      keeps sending TransactionPending, the receiver of the original
      TransactionRequest SHOULD implement a management protection mechanism
      in order to trigger the appropriate recovery actions. The sender of
      the original TransactionRequest may keep track of the number of
      received Pendings and initiate corrective actions
   
   8.3   Messages
   
      Multiple Transactions can be concatenated into a Message. Messages
      have a header, which includes the identity of the sender. The Message
      Identifier (MID) of a message is set to a provisioned name (e.g.
      domain address/domain name/device name) of the entity transmitting
      the message. Domain name is a suggested default. An H.248.1 entity
      (MG/MGC) must consistently use the same MID in all messages it
      originates for the duration of control association with the peer
      (MGC/MG).
   
      Every Message contains a Version Number identifying the version of
      the protocol the message conforms to. Versions consist of one or two
      digits, beginning with version 1. The current version of the protocol
      is Version 2.
   
      The transactions in a message are treated independently. There is no
      order implied; there is no application or protocol acknowledgement of
      a message. A message is essentially a transport mechanism.  For
      example, message X containing transaction requests A, B, and C may be
      responded to with message Y containing replies to A and C and message
      Z containing the reply to B. Likewise, message L containing request D
      and message M containing request E may be responded to with message N
      containing replies to both D and E.
   
   
   9  TRANSPORT
   
      The transport mechanism for the protocol SHOULD allow the reliable
      transport of transactions between a MGC and MG. The transport shall
      remain independent of what particular commands are being sent and
      shall be applicable to all application states. There are several
      transports defined for the protocol, which are defined in Annexes to
   
   
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      this Recommendation and other Recommendations of the H.248 sub-series
      (e.g. H.248.4 and H.248.5). Additional Transports may be defined as
      additional Recommendations of the H.248 sub-series. For transport of
      the protocol over IP, MGCs shall implement both TCP and UDP/ALF, a MG
      shall implement TCP or UDP/ALF or both.
   
      The MG is provisioned with a name or address (such as DNS name or IP
      address) of a primary and zero or more secondary MGCs (see 7.2.8)
      that is the address the MG uses to send messages to the MGC. If TCP
      or UDP is used as the protocol transport and the port to which the
      initial ServiceChange request is to be sent is not otherwise known,
      that request SHOULD be sent to the default port number for the
      protocol. This port number is 2944 for text-encoded operation or 2945
      for binary-encoded operation, for either UDP or TCP. The MGC receives
      the message containing the ServiceChange request from the MG and can
      determine the MG's address from it. As described in 7.2.8, either the
      MG or the MGC may supply an address in the ServiceChangeAddress
      parameter to which subsequent transaction requests must be addressed,
      but responses (including the response to the initial ServiceChange
      request) must always be sent back to the address which was the source
      of the corresponding request. For example, in IP networks, this is
      the source address in the IP header and the source port number in the
      TCP/UDP/SCTP header.
   
   9.1   Ordering of Commands
   
      This Recommendation does not mandate that the underlying transport
      protocol guarantees the sequencing of transactions sent to an entity.
      This property tends to maximize the timeliness of actions, but it has
      a few drawbacks. For example:
   
      -  Notify commands may be delayed and arrive at the MGC after the
         transmission of a new command changing the EventsDescriptor.
   
      -  If a new command is transmitted before a previous one is
         acknowledged, there is no guarantee that prior command will be
         executed before the new one.
   
      Media Gateway Controllers that want to guarantee consistent operation
      of the Media Gateway may use the following rules. These rules are
      with respect to commands that are in different transactions. Commands
      that are in the same transaction are executed in order (see clause
      8).
   
      1) When a Media Gateway handles several Terminations, commands
         pertaining to the different Terminations may be sent in parallel,
         for example following a model where each Termination (or group of
         Terminations) is controlled by its own process or its own thread.
   
   
   
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      2) On a Termination, there SHOULD normally be at most one outstanding
         command (Add or Modify or Move), unless the outstanding commands
         are in the same transaction. However, a Subtract command may be
         issued at any time. In consequence, a Media Gateway may sometimes
         receive a Modify command that applies to a previously subtracted
         Termination. Such commands SHOULD be ignored, and an error code
         SHOULD be returned.
   
      3) For transports that do not guarantee in-sequence delivery of
         messages (i.e. UDP), there SHOULD normally be on a given
         Termination at most one outstanding Notify command at any time.
   
      4) In some cases, an implicitly or explicitly wildcarded Subtract
         command that applies to a group of Terminations may step in front
         of a pending Add command. The Media Gateway Controller SHOULD
         individually delete all Terminations for which an Add command was
         pending at the time of the global Subtract command. Also, new Add
         commands for Terminations named by the wildcarding (or implied in
         a Multiplex descriptor) SHOULD not be sent until the wildcarded
         Subtract command is acknowledged.
   
      5) AuditValue and AuditCapability are not subject to any sequencing.
   
      6) ServiceChange shall always be the first command sent by a MG as
         defined by the restart procedure. Any other command or response
         must be delivered after this ServiceChange command.
   
      These rules do not affect the command responder, which SHOULD always
      respond to commands.
   
   9.2   Protection against Restart Avalanche
   
      In the event that a large number of Media Gateways are powered on
      simultaneously and they were to all initiate a ServiceChange
      transaction, the Media Gateway Controller would very likely be
      swamped, leading to message losses and network congestion during the
      critical period of service restoration. In order to prevent such
      avalanches, the following behaviour is suggested:
   
      1) When a Media Gateway is powered on, it SHOULD initiate a restart
         timer to a random value, uniformly distributed between 0 and a
         maximum waiting delay (MWD). Care SHOULD be taken to avoid
         synchronicity of the random number generation between multiple
         Media Gateways that would use the same algorithm.
   
      2) The Media Gateway SHOULD then wait for either the end of this
         timer or the detection of a local user activity, such as for
         example an off-hook transition on a residential Media Gateway.
   
   
   
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      3) When the timer elapses, or when an activity is detected, the Media
         Gateway SHOULD initiate the restart procedure.
   
      The restart procedure simply requires the MG to guarantee that the
      first message that the Media Gateway Controller sees from this MG is
      a ServiceChange message informing the Media Gateway Controller about
      the restart.
   
      NOTE - The value of MWD is a configuration parameter that depends on
      the type of the Media Gateway. The following reasoning may be used to
      determine the value of this delay on residential gateways.
   
      Media Gateway Controllers are typically dimensioned to handle the
      peak hour traffic load, during which, in average, 10% of the lines
      will be busy, placing calls whose average duration is typically 3
      minutes. The processing of a call typically involves 5 to 6 Media
      Gateway Controller transactions between each Media Gateway and the
      Media Gateway Controller. This simple calculation shows that the
      Media Gateway Controller is expected to handle 5 to 6 transactions
      for each Termination, every 30 minutes on average, or, to put it
      otherwise, about one transaction per Termination every 5 to 6 minutes
      on average. This suggests that a reasonable value of MWD for a
      residential gateway would be 10 to 12 minutes. In the absence of
      explicit configuration, residential gateways SHOULD adopt a value of
      600 seconds for MWD.
   
      The same reasoning suggests that the value of MWD SHOULD be much
      shorter for trunking gateways or for business gateways, because they
      handle a large number of Terminations, and also because the usage
      rate of these Terminations is much higher than 10% during the peak
      busy hour, a typical value being 60%. These Terminations, during the
      peak hour, are this expected to contribute about one transaction per
      minute to the Media Gateway Controller load. A reasonable algorithm
      is to make the value of MWD per "trunk" Termination six times shorter
      than the MWD per residential gateway, and also inversely proportional
      to the number of Terminations that are being restarted. For example
      MWD SHOULD be set to 2.5 seconds for a gateway that handles a T1
      line, or to 60 milliseconds for a gateway that handles a T3 line.
   
   
   10 SECURITY CONSIDERATIONS
   
      This clause covers security when using the protocol in an IP
      environment.
   
   10.1  Protection of Protocol Connections
   
      A security mechanism is clearly needed to prevent unauthorized
      entities from using the protocol defined in this Recommendation for
   
   
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      setting up unauthorized calls or interfering with authorized calls.
      The security mechanism for the protocol when transported over IP
      networks is IPsec [RFC 2401 to RFC 2411].
   
      The AH header [RFC 2402] affords data origin authentication,
      connectionless integrity and optional anti-replay protection of
      messages passed between the MG and the MGC. The ESP header [RFC 2406]
      provides confidentiality of messages, if desired. For instance, the
      ESP encryption service SHOULD be requested if the session
      descriptions are used to carry session keys, as defined in SDP.
   
      Implementations of the protocol defined in this Recommendation
      employing the ESP header SHALL comply with section 5 of [RFC 2406],
      which defines a minimum set of algorithms for integrity checking and
      encryption. Similarly, implementations employing the AH header SHALL
      comply with section 5 of [RFC 2402], which defines a minimum set of
      algorithms for integrity checking using manual keys.
   
      Implementations SHOULD use IKE [RFC 2409] to permit more robust
      keying options. Implementations employing IKE SHOULD support
      authentication with RSA signatures and RSA public key encryption.
   
   10.2  Interim AH scheme
   
      Implementation of IPsec requires that the AH or ESP header be
      inserted immediately after the IP header. This cannot be easily done
      at the application level. Therefore, this presents a deployment
      problem for the protocol defined in this Recommendation where the
      underlying network implementation does not support IPsec.
   
      As an interim solution, an optional AH header is defined within the
      H.248.1 protocol header. The header fields are exactly those of the
      SPI, SEQUENCE NUMBER and DATA fields as defined in [RFC 2402]. The
      semantics of the header fields are the same as the "transport mode"
      of [RFC 2402], except for the calculation of the Integrity Check
      Value (ICV). In IPsec, the ICV is calculated over the entire IP
      packet including the IP header. This prevents spoofing of the IP
      addresses. To retain the same functionality, the ICV calculation
      SHOULD be performed across all the transactions (concatenated) in the
      message prepended by a synthesized IP header consisting of a 32-bit
      source IP address, a 32-bit destination address and a 16-bit UDP
      destination port encoded as 20 hex digits. When the interim AH
      mechanism is employed when TCP is the transport Layer, the UDP Port
      above becomes the TCP port, and all other operations are the same.
   
      Implementations of the H.248.1 protocol SHALL implement IPsec where
      the underlying operating system and the transport network supports
      IPsec. Implementations of the protocol using IPv4 SHALL implement the
      interim AH scheme. However, this interim scheme SHALL NOT be used
   
   
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      when the underlying network layer supports IPsec. IPv6
      implementations are assumed to support IPsec and SHALL NOT use the
      interim AH scheme.
   
      All implementations of the interim AH mechanism SHALL comply with
      section 5 of RFC 2402 which defines a minimum set of algorithms for
      integrity checking using manual keys.
   
      The interim AH interim scheme does not provide protection against
      eavesdropping, thus forbidding third parties from monitoring the
      connections set up by a given Termination. Also, it does not provide
      protection against replay attacks. These procedures do not
      necessarily protect against denial of service attacks by misbehaving
      MGs or misbehaving MGCs. However, they will provide an identification
      of these misbehaving entities, which SHOULD then be deprived of their
      authorization through maintenance procedures.
   
   10.3  Protection of Media Connections
   
      The protocol allows the MGC to provide MGs with "session keys" that
      can be used to encrypt the audio messages, protecting against
      eavesdropping.
   
      A specific problem of packet networks is "uncontrolled barge-in".
      This attack can be performed by directing media packets to the IP
      address and UDP port used by a connection. If no protection is
      implemented, the packets must be decompressed and the signals must be
      played on the "line side".
   
      A basic protection against this attack is to only accept packets from
      known sources, checking for example that the IP source address and
      UDP source port match the values announced in the Remote descriptor.
      This has two inconveniences: it slows down connection establishment
      and it can be fooled by source spoofing:
   
      -  To enable the address-based protection, the MGC must obtain the
         remote session description of the egress MG and pass it to the
         ingress MG. This requires at least one network round trip, and
         leaves us with a dilemma: either allow the call to proceed without
         waiting for the round trip to complete, and risk for example,
         "clipping" a remote announcement, or wait for the full round trip
         and settle for slower call-set up procedures.
   
      -  Source spoofing is only effective if the attacker can obtain valid
         pairs of source destination addresses and ports, for example by
         listening to a fraction of the traffic. To fight source spoofing,
         one could try to control all access points to the network. But
         this is in practice very hard to achieve.
   
   
   
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      An alternative to checking the source address is to encrypt and
      authenticate the packets, using a secret key that is conveyed during
      the call set-up procedure. This will not slow down the call set-up,
      and provides strong protection against address spoofing.
   
   
   11 MG-MGC CONTROL INTERFACE
   
      The control association between MG and MGC is initiated at MG cold
      start, and announced by a ServiceChange message, but can be changed
      by subsequent events, such as failures or manual service events.
   
      NOTE - While the protocol does not have an explicit mechanism to
      support multiple MGCs controlling a physical MG, it has been designed
      to support the multiple logical MG (within a single physical MG) that
      can be associated with different MGCs.
   
   11.1  Multiple Virtual MGs
   
      A physical Media Gateway may be partitioned into one or more Virtual
      MGs. A virtual MG consists of a set of statically partitioned
      physical Terminations and/or sets of ephemeral Terminations. A
      physical Termination is controlled by one MGC. The model does not
      require that other resources be statically allocated, just
      Terminations. The mechanism for allocating Terminations to virtual
      MGs is a management method outside the scope of the protocol. Each of
      the virtual MGs appears to the MGC as a complete MG client.
   
      A physical MG may have only one network interface, which must be
      shared across virtual MGs. In such a case, the packet/cell side
      Termination is shared. It SHOULD be noted however, that in use, such
      interfaces require an ephemeral instance of the Termination to be
      created per flow, and thus sharing the Termination is
      straightforward. This mechanism does lead to a complication, namely
      that the MG must always know which of its controlling MGCs SHOULD be
      notified if an event occurs on the interface.
   
      In normal operation, the Virtual MG will be instructed by the MGC to
      create network flows (if it is the originating side), or to expect
      flow requests (if it is the terminating side), and no confusion will
      arise. However, if an unexpected event occurs, the Virtual MG must
      know what to do with respect to the physical resources it is
      controlling.
   
      If recovering from the event requires manipulation of a physical
      interface's state, only one MGC SHOULD do so. These issues are
      resolved by allowing any of the MGCs to create EventsDescriptors to
      be notified of such events, but only one MGC can have read/write
      access to the physical interface properties; all other MGCs have
   
   
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      read-only access. The management mechanism is used to designate which
      MGC has read/write capability, and is designated the Master MGC.
   
      Each virtual MG has its own Root Termination. In most cases the
      values for the properties of the Root Termination are independently
      settable by each MGC. Where there can only be one value, the
      parameter is read-only to all but the Master MGC.
   
      ServiceChange may only be applied to a Termination or set of
      Terminations partitioned to the Virtual MG or created (in the case of
      ephemeral Terminations) by that Virtual MG.
   
   11.2  Cold start
   
      A MG is pre-provisioned by a management mechanism outside the scope
      of this protocol with a primary and (optionally) an ordered list of
      secondary MGCs. Upon a cold start of the MG, it will issue a
      ServiceChange command with a "Restart" method, on the Root
      Termination to its primary MGC. If the MGC accepts the MG, it sends a
      Transaction Reply not including a ServiceChangeMgcId parameter. If
      the MGC does not accept the MGÆs registration, it sends a Transaction
      Reply, providing the address of an alternate MGC to be contacted by
      including a ServiceChangeMgcId parameter.
   
      If the MG receives a Transaction Reply that includes a
      ServiceChangeMgcId parameter, it sends a ServiceChange to the MGC
      specified in the ServiceChangeMgcId. It continues this process until
      it gets a controlling MGC to accept its registration, or it fails to
      get a reply. Upon failure to obtain a reply, either from the primary
      MGC, or a designated successor, the MG tries its pre-provisioned
      secondary MGCs, in order. If the MG is unable to establish a control
      relationship with any MGC, it shall wait a random amount of time as
      described in 9.2 and then start contacting its primary, and if
      necessary, its secondary MGCs again.
   
      It is possible that the reply to a ServiceChange with Restart will be
      lost, and a command will be received by the MG prior to the receipt
      of the ServiceChange response. The MG shall issue Error 505 - Command
      Received before Restart Response.
   
   11.3  Negotiation of protocol version
   
      A ServiceChange command from a MG that registers with an MGC shall
      contain the version number of the protocol supported by the MG in the
      ServiceChangeVersion parameter. Regardless of the version placed in
      the ServiceChangeVersion parameter the message containing the command
      shall be encoded as a version 1 message. Upon receiving such a
      message, if the MGC supports only a lower version, then the MGC shall
      send a ServiceChangeReply with the lower version and thereafter all
   
   
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      the messages between MG and MGC shall conform to the lower version of
      the protocol. If the MG is unable to comply and it has established a
      transport connection to the MGC, it SHOULD close that connection. In
      any event, it SHOULD reject all subsequent requests from the MGC with
      Error 406 - "Version Not Supported".
   
      If the MGC supports a higher version than the MG but is able to
      support the lower version proposed by the MG, it shall send a
      ServiceChangeReply with the lower version and thereafter all the
      messages between MG and MGC shall conform to the lower version of the
      protocol. If the MGC is unable to comply, it shall reject the
      association, with Error 406 - "Version Not Supported".
   
      Protocol version negotiation may also occur at "handoff" and
      "failover" ServiceChanges.
   
      When extending the protocol with new versions, the following rules
      SHOULD be followed:
   
      1) Existing protocol elements, i.e. procedures, parameters,
         descriptor, property, values, SHOULD not be changed unless a
         protocol error needs to be corrected or it becomes necessary to
         change the operation of the service that is being supported by the
         protocol.
   
      2) The semantics of a command, a parameter, a descriptor, a property,
         or a value SHOULD not be changed.
   
      3) Established rules for formatting and encoding messages and
         parameters SHOULD not be modified.
   
      4) When information elements are found to be obsolete they can be
         marked as not used. However, the identifier for that information
         element will be marked as reserved. In that way it can not be used
         in future versions.
   
   11.4  Failure of a MG
   
      If a MG fails, but is capable of sending a message to the MGC, it
      sends a ServiceChange with an appropriate method (graceful or forced)
      and specifies the Root TerminationID. When it returns to service, it
      sends a ServiceChange with a "Restart" method.
   
      Allowing the MGC to send duplicate messages to both MGs accommodates
      pairs of MGs that are capable of redundant failover of one of the
      MGs. Only the Working MG shall accept or reject transactions. Upon
      failover, the primary MG sends a ServiceChange command with a
      "Failover" method and a "MG Impending Failure" reason. The MGC then
      uses the secondary MG as the active MG. When the error condition is
   
   
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      repaired, the Working MG can send a "ServiceChange" with a "Restart"
      method.
   
      Note: Redundant failover MGs require a reliable transport, because
      the protocol provides no means for a secondary MG running ALF to
      acknowledge messages sent from the MGC.
   
   11.5  Failure of an MGC
   
      If the MG detects a failure of its controlling MGC, it attempts to
      contact the next MGC on its pre-provisioned list. It starts its
      attempts at the beginning (primary MGC), unless that was the MGC that
      failed, in which case it starts at its first secondary MGC. It sends
      a ServiceChange message with a "Failover" method and a " MGC
      Impending Failure" reason. If the MG is unable to establish a control
      relationship with any MGC, it shall wait a random amount of time as
      described in section 9.2 and then start again contacting its primary,
      and (if necessary) its secondary MGCs. When contacting its previously
      controlling MGC, the MG sends the ServiceChange message with
      "Disconnected" method.
   
      In partial failure, or for manual maintenance reasons, an MGC may
      wish to direct its controlled MGs to use a different MGC. To do so,
      it sends a ServiceChange method to the MG with a "HandOff" method,
      and its designated replacement in ServiceChangeMgcId. If "HandOff" is
      supported, the MG shall send a ServiceChange message with a "Handoff"
      method and a "MGC directed change" reason to the designated MGC. If
      it fails to get a reply from the designated MGC, the MG shall behave
      as if its MGC failed, and start contacting secondary MGCs as
      specified in the previous paragraph. If the MG is unable to establish
      a control relationship with any MGC, it shall wait a random amount of
      time as described in 9.2 and then start contacting its primary, and
      if necessary, its secondary MGCs again.
   
      No recommendation is made on how the MGCs involved in the Handoff
      maintain state information; this is considered to be out of scope of
      this Recommendation. The MGC and MG may take the following steps when
      Handoff occurs. When the MGC initiates a HandOff, the handover SHOULD
      be transparent to Operations on the Media Gateway. Transactions can
      be executed in any order, and could be in progress when the
      ServiceChange is executed. Accordingly, commands in progress continue
      and replies to all commands from the original MGC must be sent to the
      transport address from which they were sent. If the service
      relationship with the sending MGC has ended, the replies SHOULD be
      discarded. The MG may receive outstanding transaction replies from
      the new MGC. No new messages shall be sent to the new MGC until the
      control association is established. Repeated transaction requests
      shall be directed to the new MGC. The MG shall maintain state on all
      Terminations and Contexts.
   
   
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      It is possible that the MGC could be implemented in such a way that a
      failed MGC is replaced by a working MGC where the identity of the new
      MGC is the same as the failed one. In such a case, ServiceChangeMgcId
      would be specified with the previous value and the MG shall behave as
      if the value was changed, and send a ServiceChange message, as above.
   
      Pairs of MGCs that are capable of redundant failover can notify the
      controlled MGs of the failover by the above mechanism.
   
   
   12 PACKAGE DEFINITION
   
      The primary mechanism for extension is by means of Packages. Packages
      define additional Properties, Events, Signals and Statistics that may
      occur on Terminations.
   
      Packages defined by IETF will appear in separate RFCs.
   
      Packages defined by ITU-T may appear in the relevant Recommendations
      (e.g. as Recommendations of the H.248 sub-series).
   
      1) A public document or a standard forum document, which can be
         referenced as the document that describes the package following
         the guideline above, SHOULD be specified.
   
      2) The document shall specify the version of the Package that it
         describes.
   
      3) The document SHOULD be available on a public web server and SHOULD
         have a stable URL. The site SHOULD provide a mechanism to provide
         comments and appropriate responses SHOULD be returned.
   
   12.1  Guidelines for defining packages
   
      Packages define Properties, Events, Signals, and Statistics.
   
      Packages may also define new error codes according to the guidelines
      given in 13.2. This is a matter of documentary convenience: the
      package documentation is submitted to IANA in support of the error
      code registration. If a package is modified, it is unnecessary to
      provide IANA with a new document reference in support of the error
      code unless the description of the error code itself is modified.
   
      Names of all such defined constructs shall consist of the PackageID
      (which uniquely identifies the package) and the ID of the item (which
      uniquely identifies the item in that package). In the text encoding
      the two shall be separated by a forward slash ("/") character.
      Example: togen/playtone is the text encoding to refer to the play
      tone signal in the tone generation package.
   
   
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      A Package will contain the following sections:
   
   12.1.1   Package
   
      Overall description of the package, specifying:
   
         Package Name: only descriptive
   
         PackageID: is an identifier
   
         Description:
   
         Version:
   
      A new version of a package can only add additional Properties,
      Events, Signals, Statistics and new possible values for an existing
      parameter described in the original package. No deletions or
      modifications shall be allowed. A version is an integer in the range
      from 1 to 99.
   
         Designed to be extended only (Optional): Yes
   
      This indicates that the package has been expressly designed to be
      extended by others, not to be directly referenced. For example, the
      package may not have any function on its own or be nonsensical on its
      own. The MG SHOULD NOT publish this PackageID when reporting
      packages.
   
         Extends (Optional): existing package Descriptor
   
      A package may extend an existing package. The version of the original
      package must be specified. When a package extends another package it
      shall only add additional Properties, Events, Signals, Statistics and
      new possible values for an existing parameter described in the
      original package. An extended package shall not redefine or overload
      an identifier defined in the original package and packages it may
      have extended (multiple levels of extension). Hence, if package B
      version 1 extends package A version 1, version 2 of B will not be
      able to extend the A version 2 if A version 2 defines a name already
      in B version 1.
   
   12.1.2   Properties
   
      Properties defined by the package, specifying:
   
         Property Name: only descriptive
   
         PropertyID: is an identifier
   
   
   
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         Description:
   
         Type: One of:
   
            Boolean
   
            String: UTF-8 string
   
            Octet String: A number of octets.  See Annex A and Annex B.3
            for encoding
   
            Integer: 4 byte signed integer
   
            Double: 8 byte signed integer
   
            Character: unicode UTF-8 encoding of a single letter. Could be
            more than one octet.
   
            Enumeration: one of a list of possible unique values (see 12.3)
   
            Sub-list: a list of several values from a list. The type of
            sub-list SHALL also be specified.  The type shall be chosen
            from the types specified in this section (with the exception of
            sub-list). For example, Type: sub-list of enumeration.  The
            encoding of sub-lists is specified in Annexes A and B.3.
   
         Possible values:
   
      A package MUST specify either a specific set of values or a
      description of how values are determined.  A package MUST also
      specify a default value or the default behaviour when the value is
      omitted from its descriptor.  For example, a package may specify that
      procedures related to the property are suspended when it value is
      omitted.  A default value (but not procedures) may be specified as
      provisionable.
   
         Defined in:
   
      Which H.248.1 descriptor the property is defined in. LocalControl is
      for stream dependent properties. TerminationState is for stream
      independent properties. These are expected to be the most common
      cases, but it is possible for properties to be defined in other
      descriptors.
   
         Characteristics: Read/Write or both, and (optionally), global:
   
      Indicates whether a property is read-only, or read-write, and if it
      is global. If Global is omitted, the property is not global. If a
   
   
   
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      property is declared as global, the value of the property is shared
      by all Terminations realizing the package.
   
   12.1.3   Events
   
      Events defined by the package, specifying:
   
         Event name: only descriptive
   
         EventID: is an identifier
   
         Description:
   
         EventsDescriptor Parameters:
   
      Parameters used by the MGC to configure the event, and found in the
      EventsDescriptor. See 12.2.
   
         ObservedEventsDescriptor Parameters:
   
      Parameters returned to the MGC in Notify requests and in replies to
      command requests from the MGC that audit ObservedEventsDescriptor,
      and found in the ObservedEventsDescriptor. See 12.2.
   
   12.1.4   Signals
   
      Signals defined by the package, specifying:
   
         Signal Name: only descriptive
   
         SignalID: is an identifier. SignalID is used in a
         SignalsDescriptor
   
         Description
   
         SignalType: one of:
   
               OO (On/Off)
   
               TO (TimeOut)
   
               BR (Brief)
   
      NOTE - SignalType may be defined such that it is dependent on the
      value of one or more parameters. The package MUST specify a default
      signal type.  If the default type is TO, the package MUST specify a
      default duration which may be provisioned.  A default duration is
      meaningless for BR.
   
   
   
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         Duration: in hundredths of seconds
   
         Additional Parameters: see 12.2
   
   12.1.5   Statistics
   
      Statistics defined by the package, specifying:
   
         Statistic name: only descriptive
   
         StatisticID: is an identifier
   
      StatisticID is used in a StatisticsDescriptor
   
         Description:
   
         Units: unit of measure, e.g. milliseconds, packets
   
   12.1.6   Procedures
   
      Additional guidance on the use of the package.
   
   
   12.2  Guidelines to defining Parameters to Events and Signals
   
         Parameter Name: only descriptive
   
         ParameterID: is an identifier. The textual ParameterID of
         parameters to Events and Signals shall not start with "EPA" and
         "SPA", respectively. The textual ParameterID shall also not be
         "ST", "Stream", "SY", "SignalType", "DR", "Duration", "NC",
         "NotifyCompletion", "KA", "Keepactive", "EB", "Embed", "DM" or
         "DigitMap".
   
         Type: One of:
   
            Boolean
   
            String: UTF-8 octet string
   
            Octet String: A number of octets.  See Annex A and Annex B.3
            for encoding
   
            Integer: 4-octet signed integer
   
            Double: 8-octet signed integer
   
            Character: unicode UTF-8 encoding of a single letter. Could be
            more than one octet.
   
   
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            Enumeration: one of a list of possible unique values (see 12.3)
   
            Sub-list: a list of several values from a list (not supported
            for statistics). The type of sub-list SHALL also be specified.
            The type shall be chosen from the types specified in this
            section (with the exception of sub-list). For example, Type:
            sub-list of enumeration.  The encoding of sub-lists is
            specified in Annexes A and B.3.
   
         Possible values:
   
      A package MUST specify either a specific set of values or a
      description of how values are determined.  A package MUST also
      specify a default value or the default behavior when the value is
      omitted from its descriptor.  For example, a package may specify that
      procedures related to the parameter are suspended when it value is
      omitted.  A default value (but not procedures) may be specified as
      provisionable.
   
         Description:
   
   12.3  Lists
   
      Possible values for parameters include enumerations. Enumerations may
      be defined in a list. It is recommended that the list be IANA
      registered so that packages that extend the list can be defined
      without concern for conflicting names.
   
   12.4  Identifiers
   
      Identifiers in text encoding shall be strings of up to 64 characters,
      containing no spaces, starting with an alphabetic character and
      consisting of alphanumeric characters and/or digits, and possibly
      including the special character underscore ("_").
   
      Identifiers in binary encoding are 2 octets long.
   
      Both text and binary values shall be specified for each identifier,
      including identifiers used as values in enumerated types.
   
   12.5  Package registration
   
      A package can be registered with IANA for interoperability reasons.
      See clause 13 for IANA considerations.
   
   
   
   
   
   
   
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   13 PROFILE DEFINITION
   
      Profiles may be specified to further define how the H.248.1 protocol
      is used and what functionality is supported by a MG. The profile
      itself specifies what options associated with H.248.1 have been used.
      For example: transport and packages used for an application.
   
      A profile is identified by a name (IANA registered) and a Version. A
      name shall be a string up to 64 characters long. Version shall be 1
      to 99.
   
      The profile itself is a document that indicates the options for a
      particular application. There is no set format for this document. The
      only mandatory element is that there SHOULD be a section indicating
      the Name and Version and a summary of the profile.
   
      Whilst the first two points below are the only mandatory sections,
      the following points SHOULD be considered for inclusion:
   
      -  Profile Identification: The name and version of the profile that
         is sent in the service change command.
   
      -  Summary: A description of what the profile is.
   
      -  Naming Conventions:
   
         - MGC/MG Naming Conventions: Addressing associated with the names
            of the MGC / MG.
   
         - Termination Names: The termination identity structure.
   
         - Digit Map Names: The names of any digit maps.
   
      -  Topology Descriptor: Is the topology descriptor used by this
         profile?
   
      -  TimeStamps: Specifies whether timestamps will be used in the
         ServiceChange and/or Notify commands.
   
      -  Transaction Timers: Specifies the values of the transaction
         timers.
   
      -  Transport: Specifies what H.248 sub-series transports are
         supported by the profile.
   
      -  Encoding: Specifies what encoding is supported by the profile.
   
   
   
   
   
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      -  Mandatory support of SDP and H.248.1 Annex C information elements:
         Specifies what SDP attributes and H.248.1 Annex C information
         elements are to be supported.
   
      -  Packages: Specifies the packages that are supported in this
         profile.
   
      Mandatory: specifies the packages that shall be supported in this
      profile.
   
      Optional: specifies the packages that may be supported in the
      profile.
   
      Package Provisioning Information: specifies the values of properties
      which are specified as provisioned (e.g. names and number of cycles
      for an H.248.7 announcement).
   
      -  Security: Specifies the security mechanisms used.
   
      -  Procedures: Specifies the procedures that are associated with the
         profile.
   
   
   14 IANA CONSIDERATIONS
   
   14.1  Packages
   
      The following considerations SHALL be met to register a package with
      IANA:
   
      1) A unique string name, unique serial number and version number is
         registered for each package. The string name is used with text
         encoding. The serial number shall be used with binary encoding.
         Serial Numbers 0x8000 to 0xFFFF are reserved for private use.
         Serial number 0 is reserved.
   
      2) A contact name, email and postal addresses for that contact shall
         be specified. The contact information shall be updated by the
         defining organization as necessary.
   
      3) A reference to a document that describes the package, which SHOULD
         be public:
   
         The document shall specify the version of the Package that it
         describes.
   
         If the document is public, it SHOULD be located on a public web
         server and SHOULD have a stable URL. The site SHOULD provide a
   
   
   
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         mechanism to provide comments and appropriate responses SHOULD be
         returned.
   
      4) Packages registered by other than recognized standards bodies
         shall have a minimum package name length of 8 characters.
   
      5) All other package names are first come-first served if all other
         conditions are met.
   
   14.2  Error codes
   
      The following considerations SHALL be met to register an error code
      with IANA:
   
      1) An error number and a one-line (80-character maximum) string is
         registered for each error.
   
      2) A complete description of the conditions under which the error is
         detected shall be included in a publicly available document. The
         description shall be sufficiently clear to differentiate the error
         from all other existing error codes.
   
      3) The document SHOULD be available on a public web server and SHOULD
         have a stable URL.
   
      4) Error numbers registered by recognized standards bodies shall have
         3- or 4-character error numbers.
   
      5) Error numbers registered by all other organizations or individuals
         shall have 4-character error numbers.
   
      6) An error number shall not be redefined nor modified except by the
         organization or individual that originally defined it, or their
         successors or assigns.
   
   14.3  ServiceChange reasons
   
      The following considerations SHALL be met to register service change
      reason with IANA:
   
      1) A one-phrase, 80-character maximum, unique reason code is
         registered for each reason.
   
      2) A complete description of the conditions under which the reason is
         used is detected shall be included in a publicly available
         document. The description shall be sufficiently clear to
         differentiate the reason from all other existing reasons.
   
   
   
   
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      3) The document SHOULD be available on a public web server and SHOULD
         have a stable URL.
   
   14.4  Profiles
   
      The following considerations SHALL be met to register a Profile with
      IANA:
   
      1) A unique string name and version number (version may be omitted
         when the profile name contains a wildcard) is registered for each
         profile.
   
      2) A contact name, email and postal addresses for that contact shall
         be specified.  The contact information shall be updated by the
         defining organization as necessary.
   
      3) Profiles registered by other than recognized standards bodies
         shall have a minimum profile name length of 6 characters.
   
      4) Profile names containing a wildcard "*"on the end of their names
         shall be accepted if the first 6 characters are fully specified.
         It is assumed that the organisation that was issued with the
         Profile name will manage the namespace associated with the
         wildcard. IANA shall not issue other profiles names within "name*"
         range.
   
      All other Profile names are first come-first served if all other
      conditions are met.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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   ANNEX A  BINARY ENCODING OF THE PROTOCOL
   
      This annex specifies the syntax of messages using the notation
      defined in Recommendation X.680; Information technology - Abstract
      Syntax Notation One (ASN.1): Specification of basic notation.
      Messages shall be encoded for transmission by applying the basic
      encoding rules specified in Recommendation X.690, Information
      Technology - ASN.1 Encoding Rules: Specification of Basic Encoding
      Rules (BER), Canonical Encoding Rules (CER) and Distinguished
      Encoding Rules.
   
   A.1   Coding of wildcards
   
      The use of wildcards ALL and CHOOSE is allowed in the protocol. This
      allows a MGC to partially specify Termination IDs and to let the MG
      choose from the values that conform to the partial specification.
      Termination IDs may encode a hierarchy of names. This hierarchy is
      provisioned. For instance, a TerminationID may consist of a trunk
      group, a trunk within the group and a circuit. Wildcarding must be
      possible at all levels. The following paragraphs explain how this is
      achieved.
   
      The ASN.1 description uses octet strings of up to 8 octets in length
      for Termination IDs. This means that Termination IDs consist of at
      most 64 bits. A fully specified Termination ID may be preceded by a
      sequence of wildcarding fields. A wildcarding field is one octet in
      length. Bit 7 (the most significant bit) of this octet specifies what
      type of wildcarding is invoked: if the bit value equals 1, then the
      ALL wildcard is used; if the bit value if 0, then the CHOOSE wildcard
      is used. Bit 6 of the wildcarding field specifies whether the
      wildcarding pertains to one level in the hierarchical naming scheme
      (bit value 0) or to the level of the hierarchy specified in the
      wildcarding field plus all lower levels (bit value 1). Bits 0 through
      5 of the wildcarding field specify the bit position in the
      Termination ID at which the wildcarding starts.
   
      We illustrate this scheme with some examples. In these examples, the
      most significant bit in a string of bits appears on the left hand
      side.
   
      Assume that Termination IDs are three octets long and that each octet
      represents a level in a hierarchical naming scheme. A valid
      Termination ID is:
   
         00000001 00011110 01010101.
   
      Addressing ALL names with prefix 00000001 00011110 is done as
      follows:
   
   
   
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         wildcarding field: 10000111
   
         Termination ID: 00000001 00011110 xxxxxxxx.
   
      The values of the bits labeled "x" is irrelevant and shall be ignored
      by the receiver.
   
      Indicating to the receiver that it must choose a name with 00011110
      as the second octet is done as follows:
   
         wildcarding fields: 00010111 followed by 00000111
   
         Termination ID: xxxxxxxx 00011110 xxxxxxxx.
   
      The first wildcard field indicates a CHOOSE wildcard for the level in
      the naming hierarchy starting at bit 23, the highest level in our
      assumed naming scheme. The second wildcard field indicates a CHOOSE
      wildcard for the level in the naming hierarchy starting at bit 7, the
      lowest level in our assumed naming scheme.
   
      Finally, a CHOOSE-wildcarded name with the highest level of the name
      equal to 00000001 is specified as follows:
   
         wildcard field: 01001111
   
         Termination ID: 0000001 xxxxxxxx xxxxxxxx .
   
      Bit value 1 at bit position 6 of the first octet of the wildcard
      field indicates that the wildcarding pertains to the specified level
      in the naming hierarchy and all lower levels.
   
      Context IDs may also be wildcarded. In the case of Context IDs,
      however, specifying partial names is not allowed. Context ID 0x0
      SHALL be used to indicate the NULL Context, Context ID 0xFFFFFFFE
      SHALL be used to indicate a CHOOSE wildcard, and Context ID
      0xFFFFFFFF SHALL be used to indicate an ALL wildcard.
   
      TerminationID 0xFFFFFFFFFFFFFFFF SHALL be used to indicate the ROOT
      Termination.
   
   A.2   ASN.1 syntax specification
   
      This subclause contains the ASN.1 specification of the H.248.1
      protocol syntax.
   
      NOTE 1 - In case a transport mechanism is used that employs
      application level framing, the definition of Transaction below
      changes. Refer to the annex or to the Recommendation of the H.248
   
   
   
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      sub-series defining the transport mechanism for the definition that
      applies in that case.
   
      NOTE 2 - The ASN.1 specification below contains a clause defining
      TerminationIDList as a sequence of TerminationIDs. The length of this
      sequence SHALL be one, except possibly when used in
      contextAuditResult.
   
      NOTE 3 - This syntax specification does not enforce all restrictions
      on element inclusions and values.  Some additional restrictions are
      stated in comments and other restrictions appear in the text of this
      recommendation.  These additional restrictions are part of the
      protocol even though not enforced by this specification.
   
      NOTE 4 - The ASN.1 module in this Annex uses octet string types to
      encode values for property parameter, signal parameter and event
      parameter values and statistics. The actual types of these values
      vary and are specified in Annex C or the relevant package definition.
   
      A value is first BER-encoded based on its type using the table below.
      The result of this BER-encoding is then encoded as an ASN.1 octet
      string, "double wrapping" the value. The format specified in Annex C
      or the package relates to BER encoding according to the following
      table:
   
          Type Specified in Package   ASN.1 BER Type
   
          String                      IA5String or UTF8String
                                      (Note 4)
   
          Integer (4 Octet)           INTEGER
   
          Double (8 octet signed int) INTEGER (Note 3)
   
          Character (UTF-8, Note 1)   IA5String
   
          Enumeration                 ENUMERATED
   
          Boolean                     BOOLEAN
   
          Unsigned Integer (Note 2)   INTEGER  (Note 3)
   
          Octet (String)              OCTET STRING
   
          Note 1: Can be more than one byte
   
          Note 2: Unsigned integer is referenced in Annex C
   
   
   
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          Note 3: The BER encoding of INTEGER does not imply the
          use of 4 bytes.
   
          Note 4: String SHOULD be encoded as IA5String when the
          contents are all ASCII characters, but as UTF8String
          if it contains any non-ASCII characters.
   
   
   
      See ITU-T Rec. X.690, 8.7, for the definition of the encoding of an
      octet string value.
   
   
      MEDIA-GATEWAY-CONTROL {itu-t(0) recommendation(0) h(8) h248(248)
      modules(0) media-gateway-control(0) version2(2)}
      DEFINITIONS AUTOMATIC TAGS ::=
      BEGIN
   
   
      MegacoMessage ::= SEQUENCE
      {
         authHeader     AuthenticationHeader OPTIONAL,
         mess           Message
      }
   
      AuthenticationHeader ::= SEQUENCE
      {
         secParmIndex   SecurityParmIndex,
         seqNum         SequenceNum,
         ad             AuthData
      }
   
      SecurityParmIndex ::= OCTET STRING(SIZE(4))
   
      SequenceNum       ::= OCTET STRING(SIZE(4))
   
      AuthData          ::= OCTET STRING (SIZE (12..32))
   
      Message ::= SEQUENCE
      {
         version           INTEGER(0..99),
         -- The version of the protocol defined here is equal to 2.
         mId               MId,  -- Name/address of message originator
         messageBody CHOICE
         {
            messageError      ErrorDescriptor,
            transactions      SEQUENCE OF Transaction
         },
   
   
   
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         ...
      }
   
      MId ::= CHOICE
      {
         ip4Address           IP4Address,
         ip6Address           IP6Address,
         domainName           DomainName,
         deviceName           PathName,
         mtpAddress           OCTET STRING(SIZE(2..4)),
          -- Addressing structure of mtpAddress:
          --     25 - 15              0
          --     |  PC           | NI |
          --     24 - 14 bits    2 bits
      -- Note: 14 bits are defined for international use.
      -- Two national options exist where the point code is 16 or 24
       -- bits.
       -- To octet align the mtpAddress, the MSBs shall be encoded as 0s.
         ...
      }
   
      DomainName ::= SEQUENCE
      {
         name        IA5String,
         -- The name starts with an alphanumeric digit followed by a
         -- sequence of alphanumeric digits, hyphens and dots.  No two
         -- dots shall occur consecutively.
         portNumber     INTEGER(0..65535) OPTIONAL
      }
   
      IP4Address ::= SEQUENCE
      {
         address        OCTET STRING (SIZE(4)),
         portNumber     INTEGER(0..65535) OPTIONAL
      }
   
      IP6Address ::= SEQUENCE
      {
         address        OCTET STRING (SIZE(16)),
         portNumber     INTEGER(0..65535) OPTIONAL
      }
   
      PathName ::= IA5String(SIZE (1..64))
      -- See A.3
   
      Transaction ::= CHOICE
      {
         transactionRequest      TransactionRequest,
         transactionPending      TransactionPending,
   
   
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         transactionReply        TransactionReply,
         transactionResponseAck  TransactionResponseAck,
            -- use of response acks is dependent on underlying transport
         ...
      }
   
      TransactionId ::= INTEGER(0..4294967295)  -- 32-bit unsigned integer
   
      TransactionRequest ::= SEQUENCE
      {
         transactionId        TransactionId,
         actions              SEQUENCE OF ActionRequest,
         ...
      }
   
      TransactionPending ::= SEQUENCE
      {
         transactionId        TransactionId,
         ...
      }
   
      TransactionReply ::= SEQUENCE
      {
         transactionId        TransactionId,
         immAckRequired       NULL OPTIONAL,
         transactionResult    CHOICE
         {
              transactionError   ErrorDescriptor,
              actionReplies      SEQUENCE OF ActionReply
         },
         ...
      }
   
      TransactionResponseAck ::= SEQUENCE OF TransactionAck
      TransactionAck ::= SEQUENCE
      {
         firstAck       TransactionId,
         lastAck        TransactionId OPTIONAL
      }
   
      ErrorDescriptor ::= SEQUENCE
      {
         errorCode      ErrorCode,
         errorText      ErrorText OPTIONAL
      }
   
      ErrorCode ::= INTEGER(0..65535)
      -- See clause 14 for IANA considerations with respect to error codes
   
   
   
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      ErrorText ::= IA5String
   
      ContextID ::= INTEGER(0..4294967295)
   
      -- Context NULL Value: 0
      -- Context CHOOSE Value: 4294967294 (0xFFFFFFFE)
      -- Context ALL Value: 4294967295 (0xFFFFFFFF)
   
   
      ActionRequest ::= SEQUENCE
      {
         contextId            ContextID,
         contextRequest       ContextRequest OPTIONAL,
         contextAttrAuditReq  ContextAttrAuditRequest OPTIONAL,
         commandRequests      SEQUENCE OF CommandRequest
      }
   
      ActionReply ::= SEQUENCE
      {
         contextId         ContextID,
         errorDescriptor   ErrorDescriptor OPTIONAL,
         contextReply      ContextRequest OPTIONAL,
         commandReply      SEQUENCE OF CommandReply
      }
   
      ContextRequest ::= SEQUENCE
      {
         priority       INTEGER(0..15) OPTIONAL,
         emergency      BOOLEAN OPTIONAL,
         topologyReq    SEQUENCE OF TopologyRequest OPTIONAL,
         ...
      }
   
      ContextAttrAuditRequest ::= SEQUENCE
      {
         topology    NULL OPTIONAL,
         emergency   NULL OPTIONAL,
         priority    NULL OPTIONAL,
         ...
      }
   
      CommandRequest ::= SEQUENCE
      {
         command           Command,
         optional          NULL OPTIONAL,
         wildcardReturn    NULL OPTIONAL,
         ...
      }
   
   
   
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      Command ::= CHOICE
      {
         addReq               AmmRequest,
         moveReq              AmmRequest,
         modReq               AmmRequest,
         -- Add, Move, Modify requests have the same parameters
         subtractReq          SubtractRequest,
         auditCapRequest      AuditRequest,
         auditValueRequest    AuditRequest,
         notifyReq            NotifyRequest,
         serviceChangeReq     ServiceChangeRequest,
         ...
      }
   
      CommandReply ::= CHOICE
      {
         addReply                AmmsReply,
         moveReply               AmmsReply,
         modReply                AmmsReply,
         subtractReply           AmmsReply,
         -- Add, Move, Modify, Subtract replies have the same parameters
         auditCapReply           AuditReply,
         auditValueReply         AuditReply,
         notifyReply             NotifyReply,
         serviceChangeReply      ServiceChangeReply,
         ...
      }
   
      TopologyRequest ::= SEQUENCE
      {
         terminationFrom         TerminationID,
         terminationTo           TerminationID,
         topologyDirection       ENUMERATED
         {
            bothway(0),
            isolate(1),
            oneway(2)
         },
         ...,
         streamID             StreamID OPTIONAL
      }
   
      AmmRequest ::= SEQUENCE
      {
         terminationID        TerminationIDList,
         descriptors          SEQUENCE OF AmmDescriptor,
         -- At most one descriptor of each type (see AmmDescriptor)
         -- allowed in the sequence.
         ...
   
   
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      }
   
      AmmDescriptor ::= CHOICE
      {
         mediaDescriptor         MediaDescriptor,
         modemDescriptor         ModemDescriptor,
         muxDescriptor           MuxDescriptor,
         eventsDescriptor        EventsDescriptor,
         eventBufferDescriptor   EventBufferDescriptor,
         signalsDescriptor       SignalsDescriptor,
         digitMapDescriptor      DigitMapDescriptor,
         auditDescriptor         AuditDescriptor,
         ...
      }
   
   
      AmmsReply ::= SEQUENCE
      {
         terminationID        TerminationIDList,
         terminationAudit     TerminationAudit OPTIONAL,
         ...
      }
   
      SubtractRequest ::= SEQUENCE
      {
         terminationID        TerminationIDList,
         auditDescriptor      AuditDescriptor OPTIONAL,
         ...
      }
   
      AuditRequest ::= SEQUENCE
      {
         terminationID        TerminationID,
         auditDescriptor      AuditDescriptor,
         ...
      }
   
      AuditReply ::= CHOICE
      {
         contextAuditResult   TerminationIDList,
         error                ErrorDescriptor,
         auditResult          AuditResult,
         ...
      }
   
      AuditResult ::= SEQUENCE
      {
   
         terminationID           TerminationID,
   
   
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         terminationAuditResult  TerminationAudit
      }
   
   
   
      TerminationAudit ::= SEQUENCE OF AuditReturnParameter
   
      AuditReturnParameter ::= CHOICE
      {
         errorDescriptor            ErrorDescriptor,
         mediaDescriptor            MediaDescriptor,
         modemDescriptor            ModemDescriptor,
         muxDescriptor              MuxDescriptor,
         eventsDescriptor           EventsDescriptor,
         eventBufferDescriptor      EventBufferDescriptor,
         signalsDescriptor          SignalsDescriptor,
         digitMapDescriptor         DigitMapDescriptor,
         observedEventsDescriptor   ObservedEventsDescriptor,
         statisticsDescriptor       StatisticsDescriptor,
         packagesDescriptor         PackagesDescriptor,
         emptyDescriptors           AuditDescriptor,
         ...
      }
   
      AuditDescriptor ::= SEQUENCE
      {
         auditToken  BIT STRING
               {
                  muxToken(0), modemToken(1), mediaToken(2),
                  eventsToken(3), signalsToken(4),
                  digitMapToken(5), statsToken(6),
                  observedEventsToken(7),
                  packagesToken(8), eventBufferToken(9)
               } OPTIONAL,
         ...,
         auditPropertyToken SEQUENCE OF IndAuditParameter OPTIONAL
      }
   
      IndAuditParameter ::= CHOICE
      {
         indaudmediaDescriptor         IndAudMediaDescriptor,
         indaudeventsDescriptor        IndAudEventsDescriptor,
         indaudeventBufferDescriptor   IndAudEventBufferDescriptor,
         indaudsignalsDescriptor       IndAudSignalsDescriptor,
         indauddigitMapDescriptor      IndAudDigitMapDescriptor,
         indaudstatisticsDescriptor    IndAudStatisticsDescriptor,
         indaudpackagesDescriptor      IndAudPackagesDescriptor,
         ...
      }
   
   
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      IndAudMediaDescriptor ::= SEQUENCE
      {
   
         termStateDescr    IndAudTerminationStateDescriptor OPTIONAL,
         streams  CHOICE
               {
                  oneStream      IndAudStreamParms,
                  multiStream    SEQUENCE OF IndAudStreamDescriptor
               } OPTIONAL,
         ...
      }
   
      IndAudStreamDescriptor ::= SEQUENCE
      {
         streamID                StreamID,
         streamParms             IndAudStreamParms
      }
   
      IndAudStreamParms ::= SEQUENCE
      {
         localControlDescriptor  IndAudLocalControlDescriptor OPTIONAL,
         localDescriptor         IndAudLocalRemoteDescriptor OPTIONAL,
         remoteDescriptor        IndAudLocalRemoteDescriptor OPTIONAL,
         ...
      }
   
      IndAudLocalControlDescriptor ::= SEQUENCE
      {
         streamMode              NULL OPTIONAL,
         reserveValue            NULL OPTIONAL,
         reserveGroup            NULL OPTIONAL,
         propertyParms           SEQUENCE OF IndAudPropertyParm OPTIONAL,
         ...
      }
   
      IndAudPropertyParm ::= SEQUENCE
      {
         name     PkgdName,
         ...
      }
   
      IndAudLocalRemoteDescriptor ::= SEQUENCE
      {
         propGroupID    INTEGER(0..65535) OPTIONAL,
         propGrps       IndAudPropertyGroup,
         ...
      }
   
   
   
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      IndAudPropertyGroup ::= SEQUENCE OF IndAudPropertyParm
   
      IndAudTerminationStateDescriptor ::= SEQUENCE
      {
         propertyParms        SEQUENCE OF IndAudPropertyParm,
         eventBufferControl   NULL OPTIONAL,
         serviceState         NULL OPTIONAL,
         ...
      }
   
      IndAudEventsDescriptor ::= SEQUENCE
      {
         requestID      RequestID OPTIONAL,
         pkgdName       PkgdName,
         streamID       StreamID OPTIONAL,
         ...
      }
   
      IndAudEventBufferDescriptor ::= SEQUENCE
      {
         eventName   PkgdName,
         streamID    StreamID OPTIONAL,
         ...
      }
   
      IndAudSignalsDescriptor ::=CHOICE
      {
         signal         IndAudSignal,
         seqSigList     IndAudSeqSigList,
         ...
      }
   
      IndAudSeqSigList ::= SEQUENCE
      {
         id             INTEGER(0..65535),
         signalList     IndAudSignal OPTIONAL
      }
   
      IndAudSignal ::= SEQUENCE
      {
         signalName     PkgdName,
         streamID       StreamID OPTIONAL,
         ...
      }
   
      IndAudDigitMapDescriptor ::= SEQUENCE
      {
         digitMapName   DigitMapNameOPTIONAL
      }
   
   
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      IndAudStatisticsDescriptor ::= SEQUENCE
      {
         statName       PkgdName
      }
   
      IndAudPackagesDescriptor ::= SEQUENCE
      {
         packageName       Name,
         packageVersion    INTEGER(0..99),
         ...
      }
   
      NotifyRequest ::= SEQUENCE
      {
         terminationID              TerminationIDList,
         observedEventsDescriptor   ObservedEventsDescriptor,
         errorDescriptor            ErrorDescriptor OPTIONAL,
         ...
      }
   
      NotifyReply ::= SEQUENCE
      {
         terminationID           TerminationIDList,
         errorDescriptor         ErrorDescriptor OPTIONAL,
         ...
      }
   
      ObservedEventsDescriptor ::= SEQUENCE
      {
         requestId               RequestID,
         observedEventLst        SEQUENCE OF ObservedEvent
      }
   
      ObservedEvent ::= SEQUENCE
      {
         eventName               EventName,
         streamID                StreamID OPTIONAL,
         eventParList            SEQUENCE OF EventParameter,
         timeNotation            TimeNotation OPTIONAL,
         ...
      }
   
      EventName ::= PkgdName
   
      EventParameter ::= SEQUENCE
      {
         eventParameterName      Name,
         value                   Value,
   
   
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         -- For use of extraInfo see the comment related to PropertyParm
         extraInfo CHOICE
         {
            relation Relation,
            range    BOOLEAN,
            sublist  BOOLEAN
         } OPTIONAL,
         ...
   
      }
   
      ServiceChangeRequest ::= SEQUENCE
      {
         terminationID           TerminationIDList,
         serviceChangeParms      ServiceChangeParm,
         ...
      }
   
      ServiceChangeReply ::= SEQUENCE
      {
         terminationID           TerminationIDList,
         serviceChangeResult     ServiceChangeResult,
         ...
      }
   
      -- For ServiceChangeResult, no parameters are mandatory.  Hence the
      -- distinction between ServiceChangeParm and ServiceChangeResParm.
   
      ServiceChangeResult ::= CHOICE
      {
         errorDescriptor            ErrorDescriptor,
         serviceChangeResParms      ServiceChangeResParm
      }
   
      WildcardField ::= OCTET STRING(SIZE(1))
   
      TerminationID ::= SEQUENCE
      {
         wildcard       SEQUENCE OF WildcardField,
         id             OCTET STRING(SIZE(1..8)),
         ...
      }
      -- See A.1 for explanation of wildcarding mechanism.
      -- Termination ID 0xFFFFFFFFFFFFFFFF indicates the ROOT Termination.
   
      TerminationIDList ::= SEQUENCE OF TerminationID
   
   
   
   
   
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      MediaDescriptor ::= SEQUENCE
      {
         termStateDescr    TerminationStateDescriptor OPTIONAL,
         streams           CHOICE
                  {
                     oneStream      StreamParms,
                     multiStream    SEQUENCE OF StreamDescriptor
                  } OPTIONAL,
         ...
      }
   
      StreamDescriptor ::= SEQUENCE
      {
         streamID                StreamID,
         streamParms             StreamParms
      }
   
      StreamParms ::= SEQUENCE
      {
         localControlDescriptor     LocalControlDescriptor OPTIONAL,
         localDescriptor            LocalRemoteDescriptor OPTIONAL,
         remoteDescriptor           LocalRemoteDescriptor OPTIONAL,
         ...
      }
   
      LocalControlDescriptor ::= SEQUENCE
      {
         streamMode        StreamMode OPTIONAL,
         reserveValue      BOOLEAN OPTIONAL,
         reserveGroup      BOOLEAN OPTIONAL,
         propertyParms     SEQUENCE OF PropertyParm,
         ...
      }
   
      StreamMode ::= ENUMERATED
      {
         sendOnly(0),
         recvOnly(1),
         sendRecv(2),
         inactive(3),
         loopBack(4),
            ...
      }
   
      -- In PropertyParm, value is a SEQUENCE OF octet string.  When sent
      -- by an MGC the interpretation is as follows:
      -- empty sequence means CHOOSE
      -- one element sequence specifies value
      -- If the sublist field is not selected, a longer sequence means
   
   
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      -- "choose one of the values" (i.e. value1 OR value2 OR ...)
      -- If the sublist field is selected,
      -- a sequence with more than one element encodes the value of a
      -- list-valued property (i.e. value1 AND value2 AND ...).
      -- The relation field may only be selected if the value sequence
      -- has length 1.  It indicates that the MG has to choose a value
      -- for the property. E.g. x > 3 (using the greaterThan
      -- value for relation) instructs the MG to choose any value larger
      -- than 3 for property x.
      -- The range field may only be selected if the value sequence
      -- has length 2.  It indicates that the MG has to choose a value
      -- in the range between the first octet in the value sequence and
      -- the trailing octet in the value sequence, including the
      -- boundary values.
      -- When sent by the MG, only responses to an AuditCapability request
      -- may contain multiple values, a range, or a relation field.
   
      PropertyParm ::= SEQUENCE
      {
         name        PkgdName,
         value       SEQUENCE OF OCTET STRING,
         extraInfo   CHOICE
         {
            relation    Relation,
            range       BOOLEAN,
            sublist     BOOLEAN
         } OPTIONAL,
         ...
      }
   
      Name ::= OCTET STRING(SIZE(2))
   
      PkgdName ::= OCTET STRING(SIZE(4))
      -- represents Package Name (2 octets) plus Property, Event,
      -- Signal Names or Statistics ID. (2 octets)
      -- To wildcard a package use 0xFFFF for first two octets, choose
      -- is not allowed. To reference native property tag specified in
      -- Annex C, use 0x0000 as first two octets.
      -- To wildcard a Property, Event, Signal, or Statistics ID, use
      -- 0xFFFF for last two octets, choose is not allowed.
      -- Wildcarding of Package Name is permitted only if Property,
      -- Event, Signal, or Statistics ID are
      -- also wildcarded.
   
      Relation ::= ENUMERATED
      {
         greaterThan(0),
         smallerThan(1),
         unequalTo(2),
   
   
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         ...
      }
   
      LocalRemoteDescriptor ::= SEQUENCE
      {
         propGrps SEQUENCE OF PropertyGroup,
         ...
      }
   
      PropertyGroup ::= SEQUENCE OF PropertyParm
   
      TerminationStateDescriptor ::= SEQUENCE
      {
         propertyParms        SEQUENCE OF PropertyParm,
         eventBufferControl   EventBufferControl OPTIONAL,
         serviceState         ServiceState OPTIONAL,
         ...
      }
   
      EventBufferControl ::= ENUMERATED
      {
         off(0),
         lockStep(1),
         ...
      }
   
      ServiceState ::= ENUMERATED
      {
         test(0),
         outOfSvc(1),
         inSvc(2),
            ...
      }
   
      MuxDescriptor   ::= SEQUENCE
      {
         muxType           MuxType,
         termList          SEQUENCE OF TerminationID,
         nonStandardData   NonStandardData OPTIONAL,
         ...
      }
   
      MuxType ::= ENUMERATED
      {
         h221(0),
         h223(1),
         h226(2),
         v76(3),
         ...,
   
   
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         nx64k(4)
      }
   
      StreamID ::= INTEGER(0..65535)   -- 16-bit unsigned integer
   
      EventsDescriptor ::= SEQUENCE
      {
         requestID      RequestID OPTIONAL,
                     -- RequestID must be present if eventList
                     -- is non empty
         eventList      SEQUENCE OF RequestedEvent,
         ...
      }
   
      RequestedEvent ::= SEQUENCE
      {
         pkgdName       PkgdName,
         streamID       StreamID OPTIONAL,
         eventAction    RequestedActions OPTIONAL,
         evParList      SEQUENCE OF EventParameter,
         ...
      }
   
      RequestedActions ::= SEQUENCE
      {
         keepActive           BOOLEAN OPTIONAL,
         eventDM              EventDM OPTIONAL,
         secondEvent          SecondEventsDescriptor OPTIONAL,
         signalsDescriptor    SignalsDescriptor OPTIONAL,
         ...
      }
   
      EventDM ::= CHOICE
      {
         digitMapName   DigitMapName,
         digitMapValue  DigitMapValue
      }
   
      SecondEventsDescriptor ::= SEQUENCE
      {
         requestID         RequestID OPTIONAL,
         eventList         SEQUENCE OF SecondRequestedEvent,
         ...
      }
   
      SecondRequestedEvent ::= SEQUENCE
      {
         pkgdName          PkgdName,
         streamID          StreamID OPTIONAL,
   
   
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         eventAction       SecondRequestedActions OPTIONAL,
         evParList         SEQUENCE OF EventParameter,
         ...
      }
   
      SecondRequestedActions ::= SEQUENCE
      {
         keepActive           BOOLEAN OPTIONAL,
         eventDM              EventDM OPTIONAL,
         signalsDescriptor    SignalsDescriptor OPTIONAL,
         ...
      }
   
      EventBufferDescriptor ::= SEQUENCE OF EventSpec
   
      EventSpec ::= SEQUENCE
      {
         eventName      EventName,
         streamID       StreamID OPTIONAL,
         eventParList   SEQUENCE OF EventParameter,
         ...
      }
   
   
      SignalsDescriptor ::= SEQUENCE OF SignalRequest
   
      SignalRequest ::= CHOICE
      {
         signal         Signal,
         seqSigList     SeqSigList,
         ...
      }
   
      SeqSigList ::= SEQUENCE
      {
         id          INTEGER(0..65535),
         signalList  SEQUENCE OF Signal
      }
   
      Signal ::= SEQUENCE
      {
         signalName        SignalName,
         streamID          StreamID OPTIONAL,
         sigType           SignalType OPTIONAL,
         duration          INTEGER (0..65535) OPTIONAL,
         notifyCompletion  NotifyCompletion OPTIONAL,
         keepActive        BOOLEAN OPTIONAL,
         sigParList        SEQUENCE OF SigParameter,
         ...
   
   
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      }
   
      SignalType ::= ENUMERATED
      {
         brief(0),
         onOff(1),
         timeOut(2),
         ...
      }
   
      SignalName ::= PkgdName
   
      NotifyCompletion ::= BIT STRING
      {
         onTimeOut(0), onInterruptByEvent(1),
         onInterruptByNewSignalDescr(2), otherReason(3)
      }
   
      SigParameter ::= SEQUENCE
      {
         sigParameterName     Name,
         value                Value,
      -- For use of extraInfo see the comment related to PropertyParm
         extraInfo CHOICE
         {
            relation Relation,
            range    BOOLEAN,
            sublist  BOOLEAN
         } OPTIONAL,
         ...
      }
   
      -- For an AuditCapReply with all events, the RequestID SHALL be ALL.
      -- ALL is represented by 0xffffffff.
   
      RequestID ::= INTEGER(0..4294967295)   -- 32-bit unsigned integer
   
      ModemDescriptor ::= SEQUENCE
      {
         mtl               SEQUENCE OF ModemType,
         mpl               SEQUENCE OF PropertyParm,
         nonStandardData   NonStandardData OPTIONAL
      }
   
      ModemType ::= ENUMERATED
      {
         v18(0),
         v22(1),
         v22bis(2),
   
   
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         v32(3),
         v32bis(4),
         v34(5),
         v90(6),
         v91(7),
         synchISDN(8),
         ...
      }
   
      DigitMapDescriptor ::= SEQUENCE
      {
         digitMapName   DigitMapName OPTIONAL,
         digitMapValue  DigitMapValue OPTIONAL
      }
   
      DigitMapName ::= Name
   
      DigitMapValue ::= SEQUENCE
      {
         startTimer        INTEGER(0..99) OPTIONAL,
         shortTimer        INTEGER(0..99) OPTIONAL,
         longTimer         INTEGER(0..99) OPTIONAL,
         digitMapBody      IA5String,
      -- Units are seconds for start, short and long timers, and
      -- hundreds of milliseconds for duration timer. Thus start,
      -- short, and long range from 1 to 99 seconds and duration
      -- from 100 ms to 9.9 s
         -- See A.3 for explanation of digit map syntax
         ...,
         durationTimer     INTEGER (0..99) OPTIONAL
      }
   
      ServiceChangeParm ::= SEQUENCE
      {
         serviceChangeMethod     ServiceChangeMethod,
         serviceChangeAddress    ServiceChangeAddress OPTIONAL,
         serviceChangeVersion    INTEGER(0..99) OPTIONAL,
         serviceChangeProfile    ServiceChangeProfile OPTIONAL,
         serviceChangeReason     Value,
      -- A serviceChangeReason consists of a numeric reason code
      -- and an optional text description.
      -- The serviceChangeReason SHALL be a string consisting of
      -- a decimal reason code, optionally followed by a single
      -- space character and a textual description string.
      -- This string is first BER-encoded as an IA5String.
      -- The result of this BER-encoding is then encoded as
      -- an ASN.1 OCTET STRING type, "double wrapping" the
      -- value
      -- as was done for package elements.
   
   
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         serviceChangeDelay      INTEGER(0..4294967295) OPTIONAL,
                                           -- 32-bit unsigned integer
         serviceChangeMgcId      MId OPTIONAL,
         timeStamp               TimeNotation OPTIONAL,
         nonStandardData         NonStandardData OPTIONAL,
         ...,
         serviceChangeInfo       AuditDescriptor OPTIONAL
      }
   
      ServiceChangeAddress ::= CHOICE
      {
         portNumber        INTEGER(0..65535),    -- TCP/UDP port number
         ip4Address        IP4Address,
         ip6Address        IP6Address,
         domainName        DomainName,
         deviceName        PathName,
         mtpAddress        OCTET STRING(SIZE(2..4)),
         ...
      }
   
      ServiceChangeResParm ::= SEQUENCE
      {
         serviceChangeMgcId      MId OPTIONAL,
         serviceChangeAddress    ServiceChangeAddress OPTIONAL,
         serviceChangeVersion    INTEGER(0..99) OPTIONAL,
         serviceChangeProfile    ServiceChangeProfile OPTIONAL,
         timestamp               TimeNotation OPTIONAL,
         ...
      }
   
      ServiceChangeMethod ::= ENUMERATED
      {
         failover(0),
         forced(1),
         graceful(2),
         restart(3),
         disconnected(4),
         handOff(5),
         ...
      }
   
      ServiceChangeProfile ::= SEQUENCE
      {
         profileName    IA5String(SIZE (1..67))
   
         -- 64 characters for name, 1 for "/", 2 for version to match ABNF
      }
   
      PackagesDescriptor ::= SEQUENCE OF PackagesItem
   
   
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      PackagesItem ::= SEQUENCE
      {
         packageName       Name,
         packageVersion    INTEGER(0..99),
         ...
      }
   
      StatisticsDescriptor ::= SEQUENCE OF StatisticsParameter
   
      StatisticsParameter ::= SEQUENCE
      {
         statName       PkgdName,
         statValue      Value OPTIONAL
      }
   
      NonStandardData ::= SEQUENCE
      {
         nonStandardIdentifier   NonStandardIdentifier,
         data                    OCTET STRING
      }
   
      NonStandardIdentifier ::= CHOICE
      {
         object            OBJECT IDENTIFIER,
         h221NonStandard   H221NonStandard,
         experimental      IA5String(SIZE(8)),
             -- first two characters SHOULD be "X-" or "X+"
         ...
      }
   
      H221NonStandard ::= SEQUENCE
      {  t35CountryCode1      INTEGER(0..255),
         t35CountryCode2      INTEGER(0..255),      -- country, as per T.35
         t35Extension         INTEGER(0..255),      -- assigned nationally
         manufacturerCode     INTEGER(0..65535), -- assigned nationally
         ...
      }
   
      TimeNotation ::= SEQUENCE
      {
         date     IA5String(SIZE(8)),  -- yyyymmdd format
         time     IA5String(SIZE(8))   -- hhmmssss format
         -- per ISO 8601:1988
      }
   
      Value ::= SEQUENCE OF OCTET STRING
   
   
   
   
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      END
   
   
   
   
      A.3   Digit maps and path names
   
      From a syntactic viewpoint, digit maps are strings with syntactic
      restrictions imposed upon them. The syntax of valid digit maps is
      specified in ABNF [RFC 2234].  The syntax for digit maps presented in
      this subclause is for illustrative purposes only. The definition of
      digitMap in Annex B takes precedence in the case of differences
      between the two.
   
      digitMap = (digitString
                   / LWSP "(" LWSP digitStringList LWSP ")" LWSP)
   
      digitStringList = digitString *( LWSP "|" LWSP digitString )
   
      digitString     = 1*(digitStringElement)
   
      digitStringElement = digitPosition [DOT]
   
      digitPosition   = digitMapLetter / digitMapRange
   
      digitMapRange   = ("x" / (LWSP "[" LWSP digitLetter LWSP "]" LWSP))
   
      digitLetter     = *((DIGIT "-" DIGIT) /digitMapLetter)
   
      digitMapLetter = DIGIT           ;digits 0-9
                / %x41-4B / %x61-6B    ;a-k and A-K
                / "L"/ "S" /  "T"      ;Inter-event timers
                                       ;(long, short, start)
                / "Z"                  ;Long duration event
   
      DOT = %x2E ; "."
      LWSP = *(WSP / COMMENT / EOL)
      WSP = SP / HTAB
      COMMENT = ";" *(SafeChar / RestChar / WSP) EOL
      EOL = (CR [LF]) / LF
      SP = %x20
      HTAB = %x09
      CR = %x0D
      LF = %x0A
   
      SafeChar = DIGIT / ALPHA / "+" / "-" / "&" / "!" / "_" / "/" /
            "'" / "?" / "@" / "^" / "`" / "~" / "*" / "$" / "\" /
            "(" / ")" / "%" / "."
   
   
   
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      RestChar = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#" /
            "<" / ">" / "=" / %x22
   
      DIGIT = %x30-39      ; digits 0 through 9
      ALPHA = %x41-5A / %x61-7A  ; A-Z, a-z
   
      A path name is also a string with syntactic restrictions imposed upon
      it.  The ABNF production defining it is copied from Annex B.
   
      ; Total length of pathNAME must not exceed 64 chars.
      pathNAME = ["*"] NAME *("/" / "*"/ ALPHA / DIGIT /"_" / "$" )
                 ["@" pathDomainName ]
   
      ; ABNF allows two or more consecutive "." although it is meaningless
      ; in a path domain name.
      pathDomainName       = (ALPHA / DIGIT / "*" )
                             *63(ALPHA / DIGIT / "-" / "*" / ".")
   
      NAME = ALPHA *63(ALPHA / DIGIT / "_" )
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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   ANNEX B  TEXT ENCODING OF THE PROTOCOL
   
   B.1   Coding of wildcards
   
      In a text encoding of the protocol, while TerminationIDs are
      arbitrary, by judicious choice of names, the wildcard character, "*"
      may be made more useful. When the wildcard character is encountered,
      it will "match" all TerminationIDs having the same previous and
      following characters (if appropriate). For example, if there were
      TerminationIDs of R13/3/1, R13/3/2 and R13/3/3, the TerminationID
      R13/3/* would match all of them. There are some circumstances where
      ALL Terminations must be referred to. The TerminationID "*" suffices,
      and is referred to as ALL. The CHOOSE TerminationID "$" may be used
      to signal to the MG that it has to create an ephemeral Termination or
      select an idle physical Termination.
   
   B.2   ABNF specification
   
      The protocol syntax is presented in ABNF according to RFC 2234.
   
      Note 1 - This syntax specification does not enforce all restrictions
      on element inclusions and values.  Some additional restrictions are
      stated in comments and other restrictions appear in the text of this
      recommendation.  These additional restrictions are part of the
      protocol even though not enforced by this specification.
   
      Note 2 - The syntax is context-dependent. For example, "Add" can be
      the AddToken or a NAME depending on the context in which it occurs.
   
      Everything in the ABNF and text encoding is case insensitive. This
      includes TerminationIDs, digitmap Ids etc. SDP is case sensitive as
      per RFC 2327.
   
      ; NOTE -- The ABNF in this section uses the VALUE construct (or lists
      ; of VALUE constructs) to encode various package element values
      ; (properties, signal parameters, etc.).  The types of these values
      ; vary and are specified the relevant package definition.  Several
      ; such types are described in section 12.2.
      ;
      ; The ABNF specification for VALUE allows a quotedString form or a
      ; collection of SafeChars.  The encoding of package element values
      ; into ABNF VALUES is specified below.  If a type's encoding allows
      ; characters other than SafeChars, the quotedString form MUST be used
      ; for all values of that type, even for specific values that consist
      ; only of SafeChars.
      ;
      ; String:  A string MUST use the quotedString form of VALUE and can
      ; contain anything allowable in the quotedString form.
      ;
   
   
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      ; Integer, Double, and Unsigned Integer:  Decimal values can be
      ; encoded using characters 0-9.  Hexadecimal values must be prefixed
      ; with '0x' and can use characters 0-9,a-f,A-F.  An octal format is
      ; not supported. Negative integers start with '-' and MUST be
      ; Decimal.  The SafeChar form of VALUE MUST be used.
      ;
      ; Character:  A UTF-8 encoding of a single letter surrounded by
      ; double quotes.
      ;
      ; Enumeration:  An enumeration MUST use the SafeChar form of VALUE
      ; and can contain anything allowable in the SafeChar form.
      ;
      ; Boolean:  Boolean values are encoded as "on" and "off" and are
      ; case insensitive.  The SafeChar form of VALUE MUST be used.
      ;
      ; Future types:  Any defined types MUST fit within
      ; the ABNF specification of VALUE.  Specifically, if a type's
      ; encoding allows characters other than SafeChars, the quotedString
      ; form MUST be used for all values of that type, even for specific
      ; values that consist only of SafeChars.
      ;
      ; Note that there is no way to use the double quote character within
      ; a value.
      ;
      ; Note that SDP disallows whitespace at the beginning of a line,
      ; Megaco ABNF allows whitespace before the beginning of the SDP in
      ; the Local/Remote descriptor.  Parsers SHOULD accept whitespace
      ; between the LBRKT following the Local/Remote token and the
      ; beginning of the SDP.
   
      megacoMessage        = LWSP [authenticationHeader SEP ] message
   
      authenticationHeader = AuthToken EQUAL SecurityParmIndex COLON
                             SequenceNum COLON AuthData
   
      SecurityParmIndex    = "0x" 8(HEXDIG)
      SequenceNum          = "0x" 8(HEXDIG)
      AuthData             = "0x" 24*64(HEXDIG)
   
      message = MegacopToken SLASH Version SEP mId SEP messageBody
      ; The version of the protocol defined here is equal to 2.
   
      messageBody          = ( errorDescriptor / transactionList )
   
      transactionList      = 1*( transactionRequest / transactionReply /
                             transactionPending / transactionResponseAck )
      ; Use of response acks is dependent on underlying transport
   
   
   
   
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      transactionPending = PendingToken EQUAL TransactionID
                              LBRKT  RBRKT
   
      transactionResponseAck = ResponseAckToken LBRKT transactionAck
                     *(COMMA transactionAck) RBRKT
      transactionAck = TransactionID / (TransactionID "-" TransactionID)
   
      transactionRequest   = TransToken EQUAL TransactionID LBRKT
                             actionRequest *(COMMA actionRequest) RBRKT
   
      actionRequest        = CtxToken EQUAL ContextID LBRKT ((
                             contextRequest [COMMA  commandRequestList])
                             / commandRequestList) RBRKT
   
      contextRequest    = ((contextProperties [COMMA contextAudit])
                  / contextAudit)
   
      contextProperties    = contextProperty *(COMMA contextProperty)
   
      ; at-most-once
      contextProperty  = (topologyDescriptor / priority / EmergencyToken)
   
      contextAudit     = ContextAuditToken LBRKT
          contextAuditProperties *(COMMA contextAuditProperties) RBRKT
   
      ; at-most-once
      contextAuditProperties = ( TopologyToken / EmergencyToken /
                                 PriorityToken )
   
      ; "O-" indicates an optional command
      ; "W-" indicates a wildcarded response to a command
      commandRequestList= ["O-"] ["W-"] commandRequest *
                           (COMMA ["O-"] ["W-"]commandRequest)
   
      commandRequest      = ( ammRequest / subtractRequest / auditRequest /
                             notifyRequest / serviceChangeRequest)
   
      transactionReply = ReplyToken EQUAL TransactionID LBRKT
                         [ ImmAckRequiredToken COMMA]
                         ( errorDescriptor / actionReplyList ) RBRKT
   
      actionReplyList      = actionReply *(COMMA actionReply )
   
      actionReply          = CtxToken EQUAL ContextID LBRKT
                             ( errorDescriptor / commandReply ) /
                            (commandReply COMMA errorDescriptor) ) RBRKT
   
      commandReply      = (( contextProperties [COMMA commandReplyList] ) /
                              commandReplyList )
   
   
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      commandReplyList     = commandReplys *(COMMA commandReplys )
   
      commandReplys        = (serviceChangeReply / auditReply / ammsReply /
                              notifyReply )
   
      ;Add Move and Modify have the same request parameters
      ammRequest           = (AddToken / MoveToken / ModifyToken ) EQUAL
                             TerminationID [LBRKT ammParameter *(COMMA
                             ammParameter) RBRKT]
   
      ;at-most-once
      ammParameter         = (mediaDescriptor / modemDescriptor /
                              muxDescriptor / eventsDescriptor /
                              signalsDescriptor / digitMapDescriptor /
                              eventBufferDescriptor / auditDescriptor)
   
      ammsReply            = (AddToken / MoveToken / ModifyToken /
                              SubtractToken ) EQUAL TerminationID [ LBRKT
                              terminationAudit RBRKT ]
   
      subtractRequest      =  SubtractToken EQUAL TerminationID
                              [ LBRKT auditDescriptor RBRKT]
   
      auditRequest         =  (AuditValueToken / AuditCapToken ) EQUAL
                              TerminationID LBRKT auditDescriptor RBRKT
   
      auditReply           = (AuditValueToken / AuditCapToken )
                             ( contextTerminationAudit  / auditOther)
   
      auditOther = EQUAL TerminationID [LBRKT terminationAudit RBRKT]
   
      terminationAudit = auditReturnParameter *(COMMA auditReturnParameter)
   
      contextTerminationAudit = EQUAL CtxToken ( terminationIDList /
                             LBRKT errorDescriptor RBRKT )
   
      auditReturnParameter = (mediaDescriptor / modemDescriptor /
         muxDescriptor / eventsDescriptor / signalsDescriptor /
         digitMapDescriptor / observedEventsDescriptor /
         eventBufferDescriptor / statisticsDescriptor /
         packagesDescriptor / errorDescriptor / auditItem)
   
      auditDescriptor = AuditToken LBRKT [ auditItem *(COMMA auditItem) ]
                                   RBRKT
   
      notifyRequest        = NotifyToken EQUAL TerminationID
                             LBRKT ( observedEventsDescriptor
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                                   [ COMMA errorDescriptor ] ) RBRKT
   
      notifyReply          = NotifyToken EQUAL TerminationID
                             [ LBRKT errorDescriptor RBRKT ]
   
      serviceChangeRequest = ServiceChangeToken EQUAL TerminationID
                             LBRKT serviceChangeDescriptor RBRKT
   
      serviceChangeReply   = ServiceChangeToken EQUAL TerminationID
                             [LBRKT (errorDescriptor /
                             serviceChangeReplyDescriptor) RBRKT]
   
      errorDescriptor   = ErrorToken EQUAL ErrorCode
                          LBRKT [quotedString] RBRKT
   
      ErrorCode            = 1*4(DIGIT) ; could be extended
   
   
      TransactionID        = UINT32
   
      ;The values 0x0, 0xFFFFFFFE and 0xFFFFFFFF are reserved.
      ContextID            = (UINT32 / "*" / "-" / "$")
   
      TerminationID        = "ROOT" / pathNAME / "$" / "*"
   
      terminationIDList  = LBRKT TerminationID *(COMMA TerminationID) RBRKT
   
   
      mId                  = (( domainAddress / domainName )
                             [":" portNumber]) / mtpAddress / deviceName
   
      ; ABNF allows two or more consecutive "." although it is meaningless
      ; in a domain name.
      domainName           = "<" (ALPHA / DIGIT) *63(ALPHA / DIGIT / "-" /
                             ".") ">"
   
      deviceName           = pathNAME
   
      domainAddress        = "[" (IPv4address / IPv6address) "]"
   
      ;RFC2373 contains the definition of IP6Addresses.
      IPv6address          = hexpart [ ":" IPv4address ]
   
      IPv4address          = V4hex DOT V4hex DOT V4hex DOT V4hex
      V4hex                = 1*3(DIGIT) ; "0".."255"
   
      ; this production, while occurring in RFC2373, is not referenced
      ; IPv6prefix           = hexpart SLASH 1*2DIGIT
      hexpart = hexseq "::" [ hexseq ] / "::" [ hexseq ] / hexseq
   
   
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      hexseq               = hex4 *( ":" hex4)
      hex4                 = 1*4HEXDIG
   
      portNumber           = UINT16
   
      ; Addressing structure of mtpAddress:
      ;     25 - 15               0
      ;    |  PC             | NI |
      ;     24 - 14 bits     2 bits
      ; Note: 14 bits are defined for international use.
      ; Two national options exist where the point code is 16 or 24 bits.
      ; To octet align the mtpAddress the MSBs shall be encoded as 0s.
      ; An octet shall be represented by 2 hex digits.
      mtpAddress           = MTPToken LBRKT 4*8 (HEXDIG) RBRKT
   
      ; Total length of pathNAME must not exceed 64 chars.
      pathNAME  = ["*"] NAME *("/" / "*"/ ALPHA / DIGIT /"_" / "$" )
                  ["@" pathDomainName ]
   
      ; ABNF allows two or more consecutive "." although it is meaningless
      ; in a path domain name.
      pathDomainName       = (ALPHA / DIGIT / "*" )
                             *63(ALPHA / DIGIT / "-" / "*" / ".")
   
   
      mediaDescriptor = MediaToken LBRKT mediaParm *(COMMA mediaParm) RBRKT
   
      ; at-most one terminationStateDescriptor
      ; and either streamParm(s) or streamDescriptor(s) but not both
      mediaParm = (streamParm / streamDescriptor /
                    terminationStateDescriptor)
   
      ; at-most-once per item
      streamParm           = ( localDescriptor / remoteDescriptor /
                              localControlDescriptor )
   
      streamDescriptor     = StreamToken EQUAL StreamID LBRKT streamParm
                             *(COMMA streamParm) RBRKT
   
      localControlDescriptor = LocalControlToken LBRKT localParm
                               *(COMMA localParm) RBRKT
   
      ; at-most-once per item except for propertyParm
      localParm = ( streamMode / propertyParm / reservedValueMode
                   / reservedGroupMode )
   
      reservedValueMode    = ReservedValueToken EQUAL ( "ON" / "OFF" )
      reservedGroupMode    = ReservedGroupToken EQUAL ( "ON" / "OFF" )
   
   
   
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      streamMode           = ModeToken EQUAL streamModes
   
      streamModes  = (SendonlyToken / RecvonlyToken / SendrecvToken /
                             InactiveToken / LoopbackToken )
   
      propertyParm         = pkgdName parmValue
      parmValue            = (EQUAL alternativeValue/ INEQUAL VALUE)
      alternativeValue     = ( VALUE
                  / LSBRKT VALUE *(COMMA VALUE) RSBRKT
                      ; sublist (i.e. A AND B AND ...)
                  / LBRKT VALUE *(COMMA VALUE) RBRKT
                      ; alternatives (i.e. A OR B OR ...)
                  /  LSBRKT VALUE COLON VALUE RSBRKT )
                      ; range
   
      INEQUAL              = LWSP (">" / "<" / "#" ) LWSP
      LSBRKT               = LWSP "[" LWSP
      RSBRKT               = LWSP "]" LWSP
   
      ; Note - The octet zero is not among the permitted characters in
      ; octet string. As the current definition is limited to SDP, and a
      ; zero octet would not be a legal character in SDP, this is not a
      ; concern.
      localDescriptor      = LocalToken LBRKT octetString RBRKT
   
      remoteDescriptor     = RemoteToken LBRKT octetString RBRKT
   
      eventBufferDescriptor= EventBufferToken [ LBRKT eventSpec
                             *( COMMA eventSpec) RBRKT ]
   
      eventSpec      = pkgdName [ LBRKT eventSpecParameter
                   *(COMMA eventSpecParameter) RBRKT ]
   
      eventSpecParameter   = (eventStream / eventOther)
   
      eventBufferControl     = BufferToken EQUAL ( "OFF" / LockStepToken )
   
      terminationStateDescriptor = TerminationStateToken LBRKT
                 terminationStateParm *( COMMA terminationStateParm ) RBRKT
   
      ; at-most-once per item except for propertyParm
      terminationStateParm =(propertyParm / serviceStates /
                              eventBufferControl )
   
      serviceStates        = ServiceStatesToken EQUAL ( TestToken /
                             OutOfSvcToken / InSvcToken )
   
      muxDescriptor        = MuxToken EQUAL MuxType  terminationIDList
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      MuxType              = ( H221Token / H223Token / H226Token / V76Token
                              / extensionParameter / Nx64kToken )
   
      StreamID             = UINT16
   
      pkgdName = (PackageName SLASH ItemID) ;specific item
                  / (PackageName SLASH "*") ;all items in package
                  / ("*" SLASH "*")         ; all items supported by the MG
      PackageName          = NAME
      ItemID               = NAME
   
      eventsDescriptor     = EventsToken [ EQUAL RequestID LBRKT
                           requestedEvent *( COMMA requestedEvent ) RBRKT ]
   
      requestedEvent       = pkgdName [ LBRKT eventParameter
                             *( COMMA eventParameter ) RBRKT ]
   
      ; at-most-once each of KeepActiveToken , eventDM and eventStream
      ;at most one of either embedWithSig or embedNoSig but not both
      ;KeepActiveToken and embedWithSig must not both be present
      eventParameter = ( embedWithSig / embedNoSig / KeepActiveToken
         /eventDM / eventStream / eventOther )
   
      embedWithSig = EmbedToken LBRKT signalsDescriptor
                      [COMMA embedFirst ] RBRKT
   
      embedNoSig   = EmbedToken LBRKT embedFirst RBRKT
   
      ; at-most-once of each
      embedFirst  = EventsToken [ EQUAL RequestID LBRKT
                secondRequestedEvent *(COMMA secondRequestedEvent) RBRKT ]
   
      secondRequestedEvent = pkgdName [ LBRKT secondEventParameter
                             *( COMMA secondEventParameter ) RBRKT ]
   
      ; at-most-once each of embedSig , KeepActiveToken, eventDM or
      ; eventStream
      ; KeepActiveToken and embedSig must not both be present
      secondEventParameter = ( embedSig / KeepActiveToken / eventDM /
                               eventStream / eventOther )
   
      embedSig  = EmbedToken LBRKT signalsDescriptor RBRKT
   
      eventStream          = StreamToken EQUAL StreamID
   
      eventOther           = eventParameterName parmValue
   
      eventParameterName   = NAME
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      eventDM              = DigitMapToken EQUAL(( digitMapName ) /
                             (LBRKT digitMapValue RBRKT ))
   
      signalsDescriptor    = SignalsToken LBRKT [ signalParm
                             *(COMMA signalParm)] RBRKT
   
      signalParm           = signalList / signalRequest
   
      signalRequest        = signalName [ LBRKT sigParameter
                            *(COMMA sigParameter) RBRKT ]
   
      signalList           = SignalListToken EQUAL signalListId LBRKT
                         signalListParm *(COMMA signalListParm) RBRKT
   
      signalListId         = UINT16
   
      ;exactly once signalType, at most once duration and every signal
      ;parameter
      signalListParm       = signalRequest
   
      signalName           = pkgdName
   
      ;at-most-once sigStream, at-most-once sigSignalType,
      ;at-most-once sigDuration, every signalParameterName at most once
      sigParameter = sigStream / sigSignalType / sigDuration / sigOther
                  / notifyCompletion / KeepActiveToken
   
      sigStream            = StreamToken EQUAL StreamID
   
      sigOther             = sigParameterName parmValue
   
      sigParameterName     = NAME
   
      sigSignalType        = SignalTypeToken EQUAL signalType
   
      signalType           = (OnOffToken / TimeOutToken / BriefToken)
   
      sigDuration          = DurationToken EQUAL UINT16
   
      notifyCompletion     = NotifyCompletionToken EQUAL (LBRKT
               notificationReason *(COMMA notificationReason) RBRKT)
   
      notificationReason   = ( TimeOutToken / InterruptByEventToken
                  / InterruptByNewSignalsDescrToken
                  / OtherReasonToken )
   
      observedEventsDescriptor = ObservedEventsToken EQUAL RequestID
                         LBRKT observedEvent *(COMMA observedEvent) RBRKT
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      ;time per event, because it might be buffered
      observedEvent        = [ TimeStamp LWSP COLON] LWSP
                             pkgdName [ LBRKT observedEventParameter
                             *(COMMA observedEventParameter) RBRKT ]
   
      ;at-most-once eventStream, every eventParameterName at most once
      observedEventParameter = eventStream / eventOther
   
      ; For an AuditCapReply with all events, the RequestID SHOULD be ALL.
      RequestID            = ( UINT32 / "*" )
   
      modemDescriptor      = ModemToken (( EQUAL modemType) /
                             (LSBRKT modemType *(COMMA modemType) RSBRKT))
                             [ LBRKT propertyParm
                            *(COMMA propertyParm) RBRKT ]
   
      ; at-most-once except for extensionParameter
      modemType            = (V32bisToken / V22bisToken / V18Token /
                              V22Token / V32Token / V34Token / V90Token /
                            V91Token / SynchISDNToken / extensionParameter)
   
      digitMapDescriptor  = DigitMapToken EQUAL
                   ( ( LBRKT digitMapValue RBRKT )
                   / (digitMapName [ LBRKT digitMapValue RBRKT ]) )
   
      digitMapName    = NAME
   
      digitMapValue   = ["T" COLON Timer COMMA] ["S" COLON Timer COMMA]
                        ["L" COLON Timer COMMA] ["Z" COLON Timer COMMA]
                        digitMap
   
      Timer                = 1*2DIGIT
      ; Units are seconds for T, S, and L timers, and hundreds of
      ; milliseconds for Z timer. Thus T, S, and L range from 1 to 99
      ; seconds and Z from 100 ms to 9.9 s
   
      digitMap = (digitString
                 / LWSP "(" LWSP digitStringList LWSP ")"  LWSP)
   
      digitStringList      = digitString *( LWSP "|" LWSP digitString )
   
      digitString          = 1*(digitStringElement)
   
      digitStringElement   = digitPosition [DOT]
   
      digitPosition        = digitMapLetter / digitMapRange
      digitMapRange  = ("x" / (LWSP "[" LWSP digitLetter LWSP "]" LWSP))
   
      digitLetter          = *((DIGIT "-" DIGIT ) / digitMapLetter)
   
   
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                         Megaco Protocol version 2            April 2003
   
   
   
      digitMapLetter       = DIGIT    ;Basic event symbols
                  / %x41-4B / %x61-6B ; a-k, A-K
                  / "L" / "S" / "T"   ;Inter-event timers
                                      ; (long, short, start)
                  / "Z"               ;Long duration modifier
   
      ; at-most-once, and DigitMapToken and PackagesToken are not allowed
      ; in AuditCapabilities command
      auditItem   = ( MuxToken / ModemToken / MediaToken /
                      SignalsToken / EventBufferToken /
                      DigitMapToken / StatsToken / EventsToken /
                      ObservedEventsToken / PackagesToken ) /
                      indAudterminationAudit)
   
      indAudterminationAudit   = indAudauditReturnParameter
                              *(COMMA indAudauditReturnParameter)
   
      indAudauditReturnParameter = (indAudmediaDescriptor / /
                     indAudeventsDescriptor /
                     indAudsignalsDescriptor /
                     indAuddigitMapDescriptor /
                     indAudeventBufferDescriptor /
                     indAudstatisticsDescriptor /
                     indAudpackagesDescriptor)
   
   
      indAudmediaDescriptor   = MediaToken LBRKT indAudmediaParm RBRKT
   
      ; at-most-once per item
      ; and either streamParm or streamDescriptor but not both
      indAudmediaParm = (indAudstreamParm / indAudstreamDescriptor /
                         indAudterminationStateDescriptor)
   
      ; at-most-once
      indAudstreamParm  = ( indAudlocalControlDescriptor )
      ; SDP too complex to pull out individual pieces for audit,
      ; hence no individual audit for Local and Remote
   
      indAudstreamDescriptor = StreamToken EQUAL StreamID
                        LBRKT indAudstreamParm RBRKT
   
      indAudlocalControlDescriptor = LocalControlToken
                        LBRKT indAudlocalParm RBRKT
   
      ; at-most-once per item
      indAudlocalParm   = ( ModeToken / pkgdName /
                      ReservedValueToken /
                      ReservedGroupToken )
   
   
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                         Megaco Protocol version 2            April 2003
   
   
   
   
      indAudterminationStateDescriptor = TerminationStateToken
                        LBRKT indAudterminationStateParm RBRKT
   
      ; at-most-once per item
      indAudterminationStateParm =(pkgdName / ServiceStatesToken /
                                    BufferToken)
   
      indAudeventBufferDescriptor= EventBufferToken
                        LBRKT indAudeventSpec RBRKT
   
      indAudeventSpec   = pkgdName [ LBRKT indAudeventSpecParameter RBRKT ]
   
      indAudeventSpecParameter   = (eventStream / eventParameterName)
   
      indAudeventsDescriptor     = EventsToken EQUAL RequestID
                        LBRKT indAudrequestedEvent RBRKT
   
      indAudrequestedEvent       = pkgdName
   
      indAudsignalsDescriptor    = SignalsToken
                        LBRKT [ indAudsignalParm ] RBRKT
   
      indAudsignalParm           = indAudsignalList / indAudsignalRequest
      indAudsignalRequest        = signalName
   
      indAudsignalList           = SignalListToken EQUAL signalListId
                        LBRKTindAudsignalListParm RBRKT
   
      indAudsignalListParm = indAudsignalRequest
   
      indAuddigitMapDescriptor   = DigitMapToken EQUAL (digitMapName )
   
      indAudstatisticsDescriptor = StatsToken LBRKT pkgdName RBRKT
   
      indAudpackagesDescriptor   = PackagesToken LBRKT packagesItem RBRKT
   
   
      serviceChangeDescriptor = ServicesToken LBRKT serviceChangeParm
                               *(COMMA serviceChangeParm) RBRKT
   
      ; each parameter at-most-once
      ; at most one of either serviceChangeAddress or serviceChangeMgcId
      ; but not both
      ; serviceChangeMethod and serviceChangeReason are REQUIRED
      serviceChangeParm    = (serviceChangeMethod / serviceChangeReason /
                             serviceChangeDelay / serviceChangeAddress /
                             serviceChangeProfile / extension / TimeStamp /
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                             serviceChangeMgcId / serviceChangeVersion /
                             auditItem)
   
      serviceChangeReplyDescriptor = ServicesToken LBRKT
                    servChgReplyParm *(COMMA servChgReplyParm) RBRKT
   
      ; at-most-once. Version is REQUIRED on first ServiceChange response
      ; at most one of either serviceChangeAddress or serviceChangeMgcId
      ; but not both
      servChgReplyParm     = (serviceChangeAddress / serviceChangeMgcId /
                             serviceChangeProfile / serviceChangeVersion /
                             TimeStamp)
   
      serviceChangeMethod  = MethodToken EQUAL (FailoverToken /
                             ForcedToken / GracefulToken / RestartToken /
                             DisconnectedToken / HandOffToken /
                             extensionParameter)
   
      ; A serviceChangeReason consists of a numeric reason code
      ; and an optional text description.
      ; A serviceChangeReason MUST be encoded using the quotedString
      ; form of VALUE.
      ; The quotedString SHALL contain a decimal reason code,
      ; optionally followed by a single space character and a
      ; textual description string.
      serviceChangeReason  = ReasonToken  EQUAL VALUE
   
      serviceChangeDelay   = DelayToken   EQUAL UINT32
   
      serviceChangeAddress = ServiceChangeAddressToken EQUAL ( mId /
                             portNumber )
   
      serviceChangeMgcId   = MgcIdToken   EQUAL mId
   
      serviceChangeProfile = ProfileToken EQUAL NAME SLASH Version
   
      serviceChangeVersion = VersionToken EQUAL Version
   
      extension            = extensionParameter parmValue
   
      packagesDescriptor   = PackagesToken LBRKT packagesItem
                             *(COMMA packagesItem) RBRKT
   
      Version              = 1*2(DIGIT)
   
      packagesItem         = NAME "-" UINT16
   
      TimeStamp            = Date "T" Time ; per ISO 8601:1988
      ; Date = yyyymmdd
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      Date                 = 8(DIGIT)
      ; Time = hhmmssss
      Time                 = 8(DIGIT)
   
      statisticsDescriptor = StatsToken LBRKT statisticsParameter
                            *(COMMA statisticsParameter ) RBRKT
   
      ;at-most-once per item
      statisticsParameter  = pkgdName [EQUAL VALUE]
   
      topologyDescriptor   = TopologyToken LBRKT topologyTriple
                             *(COMMA topologyTriple) RBRKT
   
      topologyTriple       = terminationA COMMA
                             terminationB COMMA topologyDirection
                             [COMMA eventStream ]
      terminationA         = TerminationID
      terminationB         = TerminationID
   
      topologyDirection    = BothwayToken / IsolateToken / OnewayToken
   
      priority             = PriorityToken EQUAL UINT16
   
      extensionParameter   = "X"  ("-" / "+") 1*6(ALPHA / DIGIT)
   
      ; octetString is used to describe SDP defined in RFC2327.
      ; Caution SHOULD be taken if CRLF in RFC2327 is used.
      ; To be safe, use EOL in this ABNF.
      ; Whenever "}" appears in SDP, it is escaped by "\", e.g. "\}"
      octetString          = *(nonEscapeChar)
      nonEscapeChar        = ( "\}" / %x01-7C / %x7E-FF )
   
      ; Note - The double-quote character is not allowed in quotedString.
      quotedString         = DQUOTE *(SafeChar / RestChar/ WSP) DQUOTE
   
      UINT16               = 1*5(DIGIT)  ; %x0-FFFF
      UINT32               = 1*10(DIGIT) ; %x0-FFFFFFFF
   
      NAME                 = ALPHA *63(ALPHA / DIGIT / "_" )
      VALUE                = quotedString / 1*(SafeChar)
   
      SafeChar             = DIGIT / ALPHA / "+" / "-" / "&" /
                             "!" / "_" / "/" / "'" / "?" / "@" /
                             "^" / "`" / "~" / "*" / "$" / "\" /
                             "(" / ")" / "%" / "|" / "."
   
      EQUAL               = LWSP %x3D LWSP ; "="
      COLON               = %x3A           ; ":"
      LBRKT               = LWSP %x7B LWSP ; "{"
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      RBRKT               = LWSP %x7D LWSP ; "}"
      COMMA               = LWSP %x2C LWSP ; ","
      DOT                 = %x2E           ; "."
      SLASH               = %x2F           ; "/"
      ALPHA               = %x41-5A / %x61-7A ; A-Z / a-z
      DIGIT               = %x30-39         ; 0-9
      DQUOTE              = %x22            ; " (Double Quote)
      HEXDIG              = ( DIGIT / "A" / "B" / "C" / "D" / "E" / "F" )
      SP                  = %x20        ; space
      HTAB                = %x09        ; horizontal tab
      CR                  = %x0D        ; Carriage return
      LF                  = %x0A        ; linefeed
      LWSP                = *( WSP / COMMENT / EOL )
      EOL                 = (CR [LF] / LF )
      WSP                 = SP / HTAB ; white space
      SEP                 = ( WSP / EOL / COMMENT) LWSP
      COMMENT             = ";" *(SafeChar/ RestChar / WSP / %x22) EOL
      RestChar            = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#" /
                             "<" / ">" / "="
   
      ; New Tokens added to sigParameter must take the format of SPA*
      ; * may be of any form i.e. SPAM
      ; New Tokens added to eventParameter must take the form of EPA*
      ; * may be of any form i.e. EPAD
   
      AddToken                   = ("Add"                   / "A")
      AuditToken                 = ("Audit"                 / "AT")
      AuditCapToken              = ("AuditCapability"       / "AC")
      AuditValueToken            = ("AuditValue"            / "AV")
      AuthToken                  = ("Authentication"        / "AU")
      BothwayToken               = ("Bothway"               / "BW")
      BriefToken                 = ("Brief"                 / "BR")
      BufferToken                = ("Buffer"                / "BF")
      CtxToken                   = ("Context"               / "C")
      ContextAuditToken          = ("ContextAudit"          / "CA")
      DigitMapToken              = ("DigitMap"              / "DM")
      DisconnectedToken          = ("Disconnected"          / "DC")
      DelayToken                 = ("Delay"                 / "DL")
      DurationToken              = ("Duration"              / "DR")
      EmbedToken                 = ("Embed"                 / "EM")
      EmergencyToken             = ("Emergency"             / "EG")
      ErrorToken                 = ("Error"                 / "ER")
      EventBufferToken           = ("EventBuffer"           / "EB")
      EventsToken                = ("Events"                / "E")
      FailoverToken              = ("Failover"              / "FL")
      ForcedToken                = ("Forced"                / "FO")
      GracefulToken              = ("Graceful"              / "GR")
      H221Token                  = ("H221" )
      H223Token                  = ("H223" )
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      H226Token                  = ("H226" )
      HandOffToken               = ("HandOff"               / "HO")
      ImmAckRequiredToken        = ("ImmAckRequired"        / "IA")
      InactiveToken              = ("Inactive"              / "IN")
      IsolateToken               = ("Isolate"               / "IS")
      InSvcToken                 = ("InService"             / "IV")
      InterruptByEventToken      = ("IntByEvent"            / "IBE")
      InterruptByNewSignalsDescrToken
                                 = ("IntBySigDescr"         / "IBS")
      KeepActiveToken            = ("KeepActive"            / "KA")
      LocalToken                 = ("Local"                 / "L")
      LocalControlToken          = ("LocalControl"          / "O")
      LockStepToken              = ("LockStep"              / "SP")
      LoopbackToken              = ("Loopback"              / "LB")
      MediaToken                 = ("Media"                 / "M")
      MegacopToken               = ("MEGACO"                / "!")
      MethodToken                = ("Method"                / "MT")
      MgcIdToken                 = ("MgcIdToTry"            / "MG")
      ModeToken                  = ("Mode"                  / "MO")
      ModifyToken                = ("Modify"                / "MF")
      ModemToken                 = ("Modem"                 / "MD")
      MoveToken                  = ("Move"                  / "MV")
      MTPToken                   = ("MTP")
      MuxToken                   = ("Mux"                   / "MX")
      NotifyToken                = ("Notify"                / "N")
      NotifyCompletionToken      = ("NotifyCompletion"      / "NC")
      Nx64kToken                 = ("Nx64Kservice"          / "N64")
      ObservedEventsToken        = ("ObservedEvents"        / "OE")
      OnewayToken                = ("Oneway"                / "OW")
      OnOffToken                 = ("OnOff"                 / "OO")
      OtherReasonToken           = ("OtherReason"           / "OR")
      OutOfSvcToken              = ("OutOfService"          / "OS")
      PackagesToken              = ("Packages"              / "PG")
      PendingToken               = ("Pending"               / "PN")
      PriorityToken              = ("Priority"              / "PR")
      ProfileToken               = ("Profile"               / "PF")
      ReasonToken                = ("Reason"                / "RE")
      RecvonlyToken              = ("ReceiveOnly"           / "RC")
      ReplyToken                 = ("Reply"                 / "P")
      RestartToken               = ("Restart"               / "RS")
      RemoteToken                = ("Remote"                / "R")
      ReservedGroupToken         = ("ReservedGroup"         / "RG")
      ReservedValueToken         = ("ReservedValue"         / "RV")
      SendonlyToken              = ("SendOnly"              / "SO")
      SendrecvToken              = ("SendReceive"           / "SR")
      ServicesToken              = ("Services"              / "SV")
      ServiceStatesToken         = ("ServiceStates"         / "SI")
      ServiceChangeToken         = ("ServiceChange"         / "SC")
      ServiceChangeAddressToken  = ("ServiceChangeAddress"  / "AD")
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      SignalListToken            = ("SignalList"            / "SL")
      SignalsToken               = ("Signals"               / "SG")
      SignalTypeToken            = ("SignalType"            / "SY")
      StatsToken                 = ("Statistics"            / "SA")
      StreamToken                = ("Stream"                / "ST")
      SubtractToken              = ("Subtract"              / "S")
      SynchISDNToken             = ("SynchISDN"             / "SN")
      TerminationStateToken      = ("TerminationState"      / "TS")
      TestToken                  = ("Test"                  / "TE")
      TimeOutToken               = ("TimeOut"               / "TO")
      TopologyToken              = ("Topology"              / "TP")
      TransToken                 = ("Transaction"           / "T")
      ResponseAckToken           = ("TransactionResponseAck" / "K")
      V18Token                   = ("V18")
      V22Token                   = ("V22")
      V22bisToken                = ("V22b")
      V32Token                   = ("V32")
      V32bisToken                = ("V32b")
      V34Token                   = ("V34")
      V76Token                   = ("V76")
      V90Token                   = ("V90")
      V91Token                   = ("V91")
      VersionToken               = ("Version"               /   "V")
   
   
      B.3   Hexadecimal octet coding
   
      Hexadecimal octet coding is a means for representing a string of
      octets as a string of hexadecimal digits, with two digits
      representing each octet. This octet encoding SHOULD be used when
      encoding octet strings in the text version of the protocol.
   
      For each octet, the 8-bit sequence is encoded as two hexadecimal
      digits. Bit 0 is the first transmitted; bit 7 is the last.
   
      Bits 7-4 are encoded as the first hexadecimal digit, with Bit 7 as
      MSB and Bit 4 as LSB. Bits 3-0 are encoded as the second hexadecimal
      digit, with Bit 3 as MSB and Bit 0 as LSB.
   
      Examples:
   
               Octet bit pattern             Hexadecimal
                                             coding
   
               00011011                      D8
   
               11100100                      27
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
               10000011 10100010 11001000    C1451390
               00001001
   
   
   
   B.4   Hexadecimal octet sequence
   
      A hexadecimal octet sequence is an even number of hexadecimal digits,
      terminated by a <CR> character.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
   ANNEX C  TAGS FOR MEDIA STREAM PROPERTIES
   
      Parameters for Local, Remote and LocalControl descriptors are
      specified as tag-value pairs if binary encoding is used for the
      protocol. This annex contains the property names (PropertyID), the
      tags (Property tag), type of the property (Type) and the values
      (Value). Values presented in the Value field when the field contains
      references shall be regarded as "information". The reference contains
      the normative values. If a value field does not contain a reference,
      then the values in that field can be considered as "normative".
   
      Tags are given as hexadecimal numbers in this annex. When setting the
      value of a property, a MGC may underspecify the value according to
      one of the mechanisms specified in 7.1.1.
   
      It is optional to support the properties in this Annex or any of its
      sub-sections. For example, only three properties from C.3 and only
      five properties from C.8 might be implemented.
   
      For type "enumeration" the value is represented by the value in
      brackets, e.g. Send(0), Receive(1). Annex C properties with the types
      "N bits" or "M Octets" SHOULD be treated as octet strings when
      encoding the protocol. Properties with "N bit integer" shall be
      treated as an integers. "String" shall be treated as an IA5String
      when encoding the protocol.
   
      When a type is smaller than one octet, the value shall be stored in
      the low-order bits of an octet string of size 1.
   
   
   C.1   General media attributes
   
   
      PropertyID   Property Type         Value
                    tag
   
      Media        1001     Enumeration  Audio(0), Video(1), Data(2)
   
      Transmission 1002     Enumeration  Send(0), Receive(1),
      mode                                 Send&Receive(2)
   
      Number of    1003     Unsigned     0-255
      Channels               integer
   
      Sampling     1004     Unsigned     0-2^32
      rate                   integer
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      PropertyID   Property Type         Value
                    tag
   
      Bitrate      1005     Integer      (0..4294967295)
   
                                           NOTE - Units of 100 bit/s.
   
      ACodec       1006     Octet string Audio Codec Type:
   
                                           Ref.: ITU-T Q.765.5
   
                                           Non-ITU-T codecs are defined
                                           with the appropriate
                                           standards organization under
                                           a defined Organizational
                                           Identitifier.
   
      Samplepp     1007     Unsigned     Maximum samples or frames
                              integer      per packet: 0..65535
   
      Silencesupp  1008     Boolean      Silence Suppression:
                                           True/False
   
      Encrypttype  1009     Octet string Ref.: ITU-T H.245
   
      Encryptkey   100A     Octet string Encryption key
                              size
                              (0..65535)   Ref.: ITU-T H.235
   
      Echocanc     100B                  Not Used. See H.248.1 E.13
                                           for an example of possible
                                           Echo Control properties.
   
      Gain         100C     Unsigned     Gain in dB: 0..65535
                              integer
   
      Jitterbuff   100D     Unsigned     Jitter buffer size in ms:
                              integer      0..65535
   
      PropDelay    100E     Unsigned     Propagation Delay: 0..65535
                              integer
                                           Maximum propagation delay in
                                           milliseconds for the bearer
                                           connection between two media
                                           gateways. The maximum delay
                                           will be dependent on the
                                           bearer technology.
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      PropertyID   Property Type         Value
                    tag
   
      RTPpayload   100F     Integer      Payload type in RTP Profile
                                           for Audio and Video
                                           Conferences with Minimal
                                           Control
   
                                           Ref.: RFC 1890
   
   
   
   
   C.2   Mux properties
   
   
      PropertyID   Property   Type       Value
                   tag
   
      H222         2001       Octet      H222LogicalChannelParameters
                              string
                                         Ref.: ITU-T H.245
   
      H223         2002       Octet      H223LogicalChannelParameters
                              string
                                         Ref.: ITU-T H.245
   
      V76          2003       Octet      V76LogicalChannelParameters
                              string
                                         Ref.: ITU-T H.245
   
      H2250        2004       Octet      H2250LogicalChannelParameters
                              string
                                         Ref.: ITU-T H.245
   
   
   
   
   C.3   General bearer properties
   
   
      PropertyID  Property   Type       Value
                  tag
   
      Mediatx     3001       Enumerati  Media Transport Type
                              on
                                         TDM Circuit(0), ATM(1), FR(2),
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                                         Ipv4(3), Ipv6(4), ...
   
      BIR         3002       4 octets   Value depends on transport
                                         technology
   
      NSAP        3003       1-20       See NSAP.
                              octets
                                         Ref.: Annex A/X.213
   
   
   
   
   C.4   General ATM properties
   
   
     PropertyID   Property  Type        Value
                  tag
   
     AESA         4001      20 octets   ATM End System Address
   
     VPVC         4002      4 octets:   VPCI/VCI
                             VPCI in
                             first two   Ref.: ITU-T Q.2931
                             least
                             significant
                             octets, VCI
                             in second
                             two octets
   
     SC           4003      Enumeration Service Category: CBR(0), nrt-
                                         VBR1(1), nrt-VBR2(2), nrt-
                                         VBR3(3), rt-VBR1(4),
                                         rt-VBR2(5), rt-VBR3(6),
                                         UBR1(7), UBR2(8), ABR(9).
   
                                         Ref.: ATM Forum UNI 4.0
   
     BCOB         4004      5-bit       Broadband Bearer Class
                             integer
                                         Ref.: ITU-T Q.2961.2
   
     BBTC         4005      7-bit       Broadband Transfer Capability
                             integer
                                         Ref.: ITU-T Q.2961.1
   
   
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
     PropertyID   Property  Type        Value
                  tag
   
     ATC          4006      Enumeration I.371 ATM Traffic Capability
   
                                         DBR(0), SBR1(1), SBR2(2),
                                         SBR3(3), ABT/IT(4), ABT/DT(5),
                                         ABR(6)
   
                                         Ref.: ITU-T I.371
   
     STC          4007      2 bits      Susceptibility to clipping:
   
                                         Bits
                                         21
                                         --
                                         00 not susceptible to clipping
                                         01 susceptible to clipping
   
                                         Ref.: ITU-T Q.2931
   
     UPCC         4008      2 bits      User Plane Connection
                                         configuration:
   
                                         Bits
                                         21
                                         --
                                         00 point-to-point
                                         01 point-to-multipoint
   
                                         Ref.: ITU-T Q.2931
   
     PCR0         4009      24-bit      Peak Cell Rate (For CLP = 0)
                             integer
                                         Ref.: ITU-T Q.2931
   
     SCR0         400A      24-bit      Sustainable Cell Rate
                             integer     (For CLP = 0)
   
                                         Ref.: ITU-T Q.2961.1
   
     MBS0         400B      24-bit      Maximum Burst Size
                             integer     (For CLP = 0)
   
                                         Ref.: ITU-T Q.2961.1
   
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
     PropertyID   Property  Type        Value
                  tag
   
     PCR1         400C      24-bit      Peak Cell Rate (For
                             integer     CLP = 0 + 1)
   
                                         Ref.: ITU-T Q.2931
   
     SCR1         400D      24-bit      Sustainable Cell Rate
                             integer     (For CLP = 0 + 1)
   
                                         Ref.: ITU-T Q.2961.1
   
     MBS1         400E      24-bit      Maximum Burst Size
                             integer     (For CLP = 0 + 1)
   
                                         Ref.: ITU-T Q.2961.1
   
     BEI          400F      Boolean     Best Effort Indicator
   
                                         Value 1 indicates that BEI is
                                         to be included in the ATM
                                         signaling; value 0 indicates
                                         that BEI is not to be included
                                         in the ATM signaling.
   
                                         Ref.: ATM Forum UNI 4.0
   
     TI           4010      Boolean     Tagging Indicator
   
                                         Value 0 indicates that tagging
                                         is not allowed; value 1
                                         indicates that tagging is
                                         requested.
   
                                         Ref.: ITU-T Q.2961.1
   
     FD           4011      Boolean     Frame Discard
   
                                         Value 0 indicates that no
                                         frame discard is allowed;
                                         value 1 indicates that frame
                                         discard is allowed.
   
                                         Ref.: ATM Forum UNI 4.0
   
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
     PropertyID   Property  Type        Value
                  tag
   
     A2PCDV       4012      24-bit      Acceptable 2-point CDV
                             integer
                                         Ref.: ITU-T Q.2965.2
   
     C2PCDV       4013      24-bit      Cumulative 2-point CDV
                             integer
                                         Ref.: ITU-T Q.2965.2
   
     APPCDV       4014      24-bit      Acceptable P-P CDV
                             integer
                                         Ref.: ATM Forum UNI 4.0
   
     CPPCDV       4015      24-bit      Cumulative P-P CDV
                             integer
                                         Ref.: ATM Forum UNI 4.0
   
     ACLR         4016      8-bit       Acceptable Cell Loss Ratio
                             integer
                                         Ref.: ITU-T Q.2965.2, ATM
                                         Forum UNI 4.0
   
     MEETD        4017      16-bit      Maximum End-to-end transit
                             integer     delay
   
                                         Ref.: ITU-T Q.2965.2, ATM
                                         Forum UNI 4.0
   
     CEETD        4018      16-bit      Cumulative End-to-end transit
                             integer     delay
   
                                         Ref.: ITU-T Q.2965.2, ATM
                                         Forum UNI 4.0
   
     QosClass     4019      Integer 0-5 QoS Class
   
                                        QoS      Meaning
                                         Class
   
                                         0        Default QoS
                                                  associated with the
                                                  ATC as defined in
                                                  ITU-T Q.2961.2
   
                                         1        Stringent
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
     PropertyID   Property  Type        Value
                  tag
   
                                        2        Tolerant
   
                                        3        Bi-level
   
                                        4        Unbounded
   
                                        5        Stringent Bi-level
   
                                        Ref.: ITU-T Q.2965.1
   
     AALtype      401A      1 octet     AAL Type
   
                                         Bits
                                         87654321
                                         --------
                                         00000000  AAL for voice
                                         00000001  AAL type 1
                                         00000010  AAL type 2
                                         00000011  AAL type 3/4
                                         00000101  AAL type 5
                                         00010000  user-defined AAL
   
                                         Ref.: ITU-T Q.2931
   
   
   
   
   C.5   Frame Relay
   
   
      PropertyID   Property   Type         Value
                    tag
   
      DLCI         5001       Unsigned     Data link connection id
                                integer
   
      CID          5002       Unsigned     sub-channel id
                                integer
   
      SID/         5003       Unsigned     silence insertion
      Noiselevel               integer      descriptor
   
      Primary      5004       Unsigned     Primary Payload Type
      Payload type             integer
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                                             Covers FAX and codecs
   
   
   
   C.6   IP
   
   
      PropertyID   Property   Type         Value
                    tag
   
      IPv4         6001       32 bits      Ipv4Address
                                Ipv4Address  Ref.: IETF RFC 791
   
      IPv6         6002       128 bits     IPv6 Address
                                             Ref.: IETF RFC 2460
   
      Port         6003       Unsigned     0..65535
                                integer
   
      Porttype     6004       Enumerated   TCP(0), UDP(1), SCTP(2)
   
   
   
   C.7   ATM AAL2
   
   
      PropertyID  Property  Type          Value
                  tag
   
      AESA        7001      20 octets     AAL2 service endpoint
                                           address as defined in the
                                           referenced Recommendation.
   
                                           ESEA
   
                                           NSEA
   
                                           Ref.: ITU-T Q.2630.1
   
      BIR         See C.3   4 octets      Served user generated
                                           reference as defined in the
                                           referenced Recommendation.
   
                                           SUGR
   
                                           Ref.: ITU-T Q.2630.1
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      PropertyID  Property  Type          Value
                  tag
   
      ALC         7002      12 octets     AAL2 link characteristics as
                                           defined in the referenced
                                           Recommendation.
   
                                           Maximum/Average CPS-SDU bit
                                           rate;
   
                                           Maximum/Average CPS-SDU size
   
                                           Ref.: ITU-T Q.2630.1
   
      SSCS        7003      I.366.2:      Service specific convergence
                                           sublayer information as
                            Audio         defined in:
                            (8 octets);   -  ITU-T Q.2630.1,
                            Multirate     and used in:
                            (3 octets),
                            or            -  ITU-T I.366.2:
                                           Audio/Multirate;
                            I.366.1:
                                           -  ITU-T I.366.1:
                            SAR-assured   SAR-assured/-unassured.
                            (14 octets);
                            SAR-unassured Ref.: ITU-T Q.2630.1,
                            (7 octets).   I.366.1 and I.366.2
   
      SUT         7004      1..254 octets Served user transport
                                           parameter as defined in the
                                           referenced Recommendation.
   
                                           Ref.: ITU-T Q.2630.1
   
      TCI         7005      Boolean       Test connection indicator as
                                           defined in the referenced
                                           Recommendation.
   
                                           Ref.: ITU-T Q.2630.1
   
      Timer_CU    7006      32-bit        Timer-CU
                            integer
                                           Milliseconds to hold
                                           partially filled cell before
                                           sending.
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      PropertyID  Property  Type          Value
                  tag
   
      MaxCPSSDU   7007      8-bit integer Maximum Common Part Sublayer
                                           Service Data Unit
   
                                           Ref.: ITU-T Q.2630.1
   
      CID         7008      8 bits        subchannel id: 0-255
   
                                           Ref.: ITU-T I.363.2
   
   
   
   C.8   ATM AAL1
   
   
      Property Property   Type     Value
      ID       tag
   
      BIR      See table  4-29     GIT (Generic Identifier Transport)
                in C.3     octets
                                     Ref.: ITU-T Q.2941.1
   
      AAL1ST   8001       1 octet  AAL1 Subtype
   
                                     Bits
                                     87654321
                                     --------
                                     00000000 null
                                     00000001 voiceband signal
                                              transport on 64 kbit/s
                                     00000010 circuit transport
                                     00000100 high-quality audio signal
                                              transport
                                     00000101 video signal transport
   
                                     Ref.: ITU-T Q.2931
   
      CBRR     8002       1 octet  CBR Rate
   
                                     Bits
                                     87654321
                                     --------
                                     00000001        64 kbit/s
                                     00000100      1544 kbit/s
                                     00000101      6312 kbit/s
                                     00000110    32 064 kbit/s
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      Property Property   Type     Value
      ID       tag
   
                                     00000111    44 736 kbit/s
                                     00001000    97 728 kbit/s
                                     00010000      2048 kbit/s
                                     00010001      8448 kbit/s
                                     00010010    34 368 kbit/s
                                     00010011   139 264 kbit/s
                                     01000000    n x 64 kbit/s
                                     01000001    n x  8 kbit/s
   
                                     Ref.: ITU-T Q.2931
   
      MULT     See table           Multiplier, or n x 64k/8k/300
                in C.9
                                     Ref.: ITU-T Q.2931
   
      SCRI     8003       1 octet  Source Clock Frequency Recovery
                                     Method
   
                                     Bits
                                     87654321
                                     --------
                                     00000000    null
                                     00000001    SRTS
                                     00000010    ACM
   
                                     Ref.: ITU-T Q.2931
   
      ECM      8004       1 octet  Error Correction Method
   
                                     Bits
                                     87654321
                                     --------
                                     00000000    null
                                     00000001    FEC - Loss
                                     00000010    FEC - Delay
   
                                     Ref.: ITU-T Q.2931
   
      SDTB     8005       16-bit   Structured Data Transfer Blocksize
                           integer
                                     Block size of SDT CBR service
   
                                     Ref.: ITU-T I.363.1
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      Property Property   Type     Value
      ID       tag
   
      PFCI     8006       8-bit    Partially filled cells identifier
                           integer
                                     1-47
   
                                     Ref.: ITU-T I.363.1
   
   
   
   C.9   Bearer capabilities
   
      The table entries referencing Recommendation Q.931 refer to the
      encoding in the bearer capability information element of Q.931, not
      to the low layer information element.
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
      TMR         9001      1 octet Transmission Medium Requirement
                                     (Q.763)
   
                                     Bits
                                     87654321
                                     --------
                                     00000000   speech
                                     00000001   spare
                                     00000010   64 kbit/s unrestricted
                                     00000011   3.1 kHz audio
                                     00000100   reserved for alternate
                                                speech (service 2) /
                                                64 kbit/s unrestricted
                                                (service 1)
                                     00000101   reserved for alternate
                                                64 kbit/s unrestricted
                                                (service 1) / speech
                                                (service 2)
                                     00000110   64 kbit/s preferred
                                     00000111   2 x 64 kbit/s
                                                unrestricted
                                     00001000   384 kbit/s unrestricted
                                     00001001  1536 kbit/s unrestricted
                                     00001010  1920 kbit/s unrestricted
                                     00001011
                                     through           spare
                                     00001111
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                    00010000    3 x 64 kbit/s
                                      through          through
                                     00101010   29 x 64 kbit/s
                                                unrestricted
                                     00101011
                                     through           spare
                                     11111111
   
                                     Ref.: ITU-T Q.763
   
      TMRSR       9002      1 octet Transmission Medium Requirement
                                     Subrate
   
                                     0  unspecified
   
                                     1  8 kbit/s
                                     2  16 kbit/s
                                     3  32 kbit/s
   
      Contcheck   9003      Boolean Continuity Check
   
                                     0  continuity check not required
                                     on this circuit
   
                                     1  continuity check required on
                                     this circuit
   
                                     Ref.: ITU-T Q.763
   
      ITC         9004      5 bits  Information Transfer Capability
   
                                     Bits
                                     54321
                                     -----
   
                                     00000   Speech
   
                                     01000   Unrestricted digital
                                                   information
   
                                     01001   Restricted digital
                                                information
   
                                     10000   3.1 kHz audio
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     10001   Unrestricted digital
                                                information with
                                                tones/announcements
   
                                     11000   Video
   
                                     All other values are reserved.
   
                                     Ref.: ITU-T Q.763
   
      TransMode   9005      2 bits  Transfer Mode
   
                                     Bits
                                     21
                                     --
                                     00 Circuit mode
                                     10 Packet mode
   
                                     Ref.: ITU-T Q.931
   
      TransRate   9006      5 bits  Transfer Rate
   
                                     Bits
                                     54321
                                     -----
                                     00000    This code shall be used
                                              for packet mode calls
                                     10000        64 kbit/s
                                     10001    2 x 64 kbit/s
                                     10011       384 kbit/s
                                     10101      1536 kbit/s
                                     10111      1920 kbit/s
                                     11000    Multirate (64 kbit/s
                                                 base rate)
   
                                     Ref.: ITU-T Q.931
   
      MULT        9007      7 bits  Rate Multiplier
   
                                     Any value from 2 to n (maximum
                                     number of B-channels)
   
                                     Ref.: ITU-T Q.931
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
      layer1prot  9008      5 bits  User Information Layer 1 Protocol
   
                                     Bits
                                     54321
                                     -----
                                     00001   ITU-T standardized rate
                                             adaption V.110 and X.30.
                                     00010   Rec. G.711 mu-law
                                     00011   Rec. G.711 A-law
                                     00100   Rec. G.726 32 kbit/s ADPCM
                                             and Rec. I.460
                                     00101   Rec. H.221 and H.242
                                     00110   Rec. H.223 and H.245
                                     00111   Non-ITU-T standardized
                                             rate adaption.
                                     01000   ITU-T standardized rate
                                             adaption V.120.
                                     01001   ITU-T standardized rate
                                             adaption X.31 HDLC flag
                                             stuffing
   
                                     All other values are reserved.
   
                                     Ref.: ITU Recommendation Q.931
      syncasync   9009      Boolean Synchronous/Asynchronous
   
                                     0  Synchronous data
                                     1  Asynchronous data
   
                                     Ref.: ITU-T Q.931
   
      negotiatio  900A      Boolean Negotiation
      n
                                     0 In-band negotiation possible
                                     1 In-band negotiation not possible
   
                                     Ref.: ITU-T Q.931
   
      Userrate    900B      5 bits  User Rate
   
                                     54321
                                     -----
                                     00000  Rate is indicated by E-bits
                                            specified in Rec. I.460 or
                                            may be negotiated in-band
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     00001  0.6 kbit/s Recs. V.6 & X.1
                                     00010  1.2 kbit/s Rec. V.6
                                     00011  2.4 kbit/s Recs. V.6 & X.1
                                     00100  3.6 kbit/s Rec. V.6
                                     00101  4.8 kbit/s Recs. V.6 & X.1
                                     00110  7.2 kbit/s Rec. V.6
                                     00111    8 kbit/s Rec. I.460
                                     01000  9.6 kbit/s Recs. V.6 & X.1
                                     01001 14.4 kbit/s Rec. V.6
                                     01010   16 kbit/s Rec. I.460
                                     01011 19.2 kbit/s Rec. V.6
                                     01100   32 kbit/s Rec. I.460
                                     01101 38.4 kbit/s Rec. V.110
                                     01110   48 kbit/s Recs. V.6 & X.1
                                     01111   56 kbit/s Rec. V.6
                                     10010 57.6 kbit/s Rec. V.14
                                                       extended
                                     10011 28.8 kbit/s Rec. V.110
                                     10100   24 kbit/s Rec. V.110
                                     10101    0.1345 kbit/s Rec. X.1
                                     10110     0.100 kbit/s Rec. X.1
   
                                     Recommendations V.6 and X.1:
                                     10111    0.075/1.2 kbit/s
                                     11000    1.2/0.075 kbit/s
                                     11001        0.050 kbit/s
                                     11010        0.075 kbit/s
                                     11011        0.110 kbit/s
                                     11100        0.150 kbit/s
                                     11101        0.200 kbit/s
                                     11110        0.300 kbit/s
   
                                     11111 12 kbit/s Rec. V.6
   
                                     All other values are reserved.
   
                                     Ref.: ITU-T Q.931
   
      INTRATE     900C      2 bits  Intermediate Rate
   
                                     Bits
                                     21
                                     --
                                     00  Not used
                                     01   8 kbit/s
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     10  16 kbit/s
                                     11  32 kbit/s
   
                                     Ref.: ITU-T Q.931
   
      nictx       900D      Boolean Network Independent Clock (NIC) on
                                     transmission
   
                                     0  Not required to send data with
                                     network independent clock
   
                                     1  Required to send data with
                                     network independent clock
   
                                     Ref.: ITU-T Q.931
   
      nicrx       900E      Boolean Network independent clock (NIC) on
                                     reception
   
                                     0  Cannot accept data with network
                                     independent clock (i.e. sender
                                     does not support this optional
                                     procedure)
   
                                     1  Can accept data with network
                                     independent clock (i.e. sender
                                     does support this optional
                                     procedure)
   
                                     Ref.: ITU-T Q.931
   
      flowconttx  900F      Boolean Flow Control on transmission (Tx)
   
                                     0  Not required to send data with
                                     flow control mechanism
   
                                     1  Required to send data with flow
                                     control mechanism
   
                                     Ref.: ITU-T Q.931
   
      flowcontrx  9010      Boolean Flow control on reception (Rx)
   
                                     0  Cannot accept data with flow
                                     control mechanism (i.e. sender
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     does not support this optional
                                     procedure)
   
                                     1  Can accept data with flow
                                     control mechanism (i.e. sender
                                     does support this optional
                                     procedure)
   
                                     Ref.: ITU-T Q.931
   
      rateadapth  9011      Boolean Rate adaption header/no header
      dr
                                     0  Rate adaption header not
                                     included
   
                                     1  Rate adaption header included
   
                                     Ref.: ITU-T Q.931
   
      multiframe  9012      Boolean Multiple frame establishment
                                     support in data link
   
                                     0  Multiple frame establishment
                                     not supported. Only UI frames
                                     allowed
   
                                     1  Multiple frame establishment
                                     supported
   
                                     Ref.: ITU-T Q.931
   
      OPMODE      9013      Boolean Mode of operation
   
                                     0  Bit transparent mode of
                                     operation
   
                                     1  Protocol sensitive mode of
                                     operation
   
                                     Ref.: ITU-T Q.931
   
      llidnegot   9014      Boolean Logical link identifier
                                     negotiation
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     0  Default, LLI = 256 only
   
                                     1  Full protocol negotiation
   
                                     Ref.: ITU-T Q.931
   
      assign      9015      Boolean Assignor/assignee
   
                                     0  Message originator is "default
                                     assignee"
   
                                     1  Message originator is "assignor
                                     only"
   
                                     Ref.: ITU-T Q.931
   
      inbandneg   9016      Boolean In-band/out-band negotiation
   
                                     0  Negotiation is done with USER
                                     INFORMATION messages on a
                                     temporary signalling connection
   
                                     1  Negotiation is done in-band
                                     using logical link zero
   
                                     Ref.: ITU-T Q.931
   
      stopbits    9017      2 bits  Number of stop bits
   
                                     Bits
                                     21
                                     --
                                     00  Not used
                                     01    1 bit
                                     10  1.5 bits
                                     11    2 bits
   
                                     Ref.: ITU-T Q.931
   
      databits    9018      2 bits  Number of data bits excluding
                                     parity bit if present
   
                                     Bits
                                     21
                                     --
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     00  Not used
                                     01  5 bits
                                     10  7 bits
                                     11  8 bits
   
                                     Ref.: ITU-T Q.931
   
      parity      9019      3 bits  Parity information
   
                                     Bits
                                     321
                                     ---
                                     000   Odd
                                     010   Even
                                     011   None
                                     100   Forced to 0
                                     101   Forced to 1
   
                                     All other values are reserved.
   
                                     Ref.: ITU-T Q.931
   
      duplexmode  901A      Boolean Mode duplex
   
                                     0  Half duplex
                                     1  Full duplex
   
                                     Ref.: ITU-T Q.931
   
      modem       901B      6 bits  Modem Type
   
                                     Bits
                                     654321
                                     ------
                                     000000
                                      through    National use
                                     000101
   
                                     010001   Recommendation V.21
                                     010010   Recommendation V.22
                                     010011   Recommendation V.22 bis
                                     010100   Recommendation V.23
                                     010101   Recommendation V.26
                                     011001   Recommendation V.26 bis
                                     010111   Recommendation V.26 ter
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     011000   RecommendationV.27
                                     011001   Recommendation V.27 bis
                                     011010   Recommendation V.27 ter
                                     011011   Recommendation V.29
                                     011101   Recommendation V.32
                                     011110   Recommendation V.34
   
                                     100000
                                      through    National use
                                     101111
   
                                     110000
                                      through    User specified
                                     111111
   
                                     Ref.: ITU-T Q.931
   
      layer2prot  901C      5 bits  User information layer 2 protocol
   
                                     Bits
                                     54321
                                     -----
   
                                     00010  Rec. Q.921 / I.441
   
                                     00110  Rec. X.25, link layer
   
                                     01100  LAN logical link control
   
                                            (ISO/IEC 8802-2)
   
                                     All other values are reserved.
   
                                     Ref.: ITU-T Q.931
   
      layer3prot  901D      5 bits  User information layer 3 protocol
   
                                     Bits
                                     54321
                                     -----
   
                                     00010  ITU-T Q.931
   
                                     00110  ITU-T X.25, packet layer
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     01011  ISO/IEC TR 9577 (Protocol
                                            identification in the
                                            network layer)
   
                                     All other values are reserved.
   
                                     Ref.: ITU-T Q.931
   
      addlayer3p  901E      Octet   Additional User Information layer
      rot                            3 protocol
   
                                     Bits  Bits
                                     4321  4321
                                     ----  ----
   
                                     1100  1100  Internet Protocol
                                                 (RFC 791)
                                                 (ISO/IEC TR 9577)
   
                                     1100  1111  Point-to-point
                                                 Protocol (RFC 1661)
   
                                     Ref.: ITU-T Q.931
   
      DialledN    901F      30      Dialled Number
                            octets
   
      DiallingN   9020      30      Dialling Number
                            octets
   
      ECHOCI      9021              Not Used. See H.248.1 E.13 for an
                                     example of possible Echo Control
                                     properties.
   
      NCI         9022      1 octet Nature of Connection Indicators
   
                                     Bits
                                     21    Satellite Indicator
                                     --
                                     00  no satellite circuit in the
                                         connection
                                     01  one satellite circuit in the
                                         connection
                                     10  two satellite circuits in the
                                         connection
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  Property
      PropertyID            Type    Value
                  tag
   
                                     11  spare
   
                                     Bits
                                     43    Continuity check indicator
                                     --
                                     00  continuity check not required
                                     01  continuity check required on
                                         this circuit
                                     10  continuity check performed on
                                         a previous circuit
                                     11  spare
   
                                     Bit
                                     5    Echo control device indicator
                                     -
                                     0  outgoing echo control device
                                        not included
                                     1  outgoing echo control device
                                        included
   
                                     Bits
                                     8 7 6    Spare
   
                                     Ref.: ITU-T Q.763
   
      USI         9023      Octet   User Service Information
                            string
                                     Ref.: ITU-T Q.763 Clause 3.57
   
   
   
   C.10  AAL5 properties
   
   
      PropertyID  Property Type       Value
                  tag
   
      FMSDU       A001     32-bit     Forward Maximum CPCS-SDU Size:
                            integer
                                       Maximum CPCS-SDU size sent in
                                       the direction from the calling
                                       user to the called user.
   
                                       Ref.: ITU-T Q.2931
   
   
   
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      BMSDU       A002     32-bit     Backwards Maximum CPCS-SDU
                            integer    Size:
   
                                       Maximum CPCS-SDU size sent in
                                       the direction from the called
                                       user to the calling user.
   
                                       Ref.: ITU-T Q.2931
   
      SSCS        See      See table  See table in C.7
                  table in in C.7
                  C.7                  Additional values:
   
                                       VPI/VCI
   
   
   
   C.11  SDP equivalents
   
   
      PropertyID    Property   Type       Value
                    tag
   
      SDP_V         B001       String     Protocol Version
   
                                           Ref.: RFC 2327
   
      SDP_O         B002       String     Owner/creator and session ID
   
                                           Ref.: RFC 2327
   
      SDP_S         B003       String     Session name
   
                                           Ref.: RFC 2327
   
      SDP_I         B004       String     Session identifier
   
                                           Ref.: RFC 2327
   
      SDP_U         B005       String     URI of descriptor
   
                                           Ref.: RFC 2327
   
      SDC_E         B006       String     email address
   
                                           Ref.: RFC 2327
   
   
   
   
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      SDP_P         B007       String     phone number
   
                                           Ref.: RFC 2327
   
      SDP_C         B008       String     Connection information
   
                                           Ref.: RFC 2327
   
      SDP_B         B009       String     Bandwidth Information
   
                                           Ref.: RFC 2327
   
      SDP_Z         B00A       String     Time zone adjustment
   
                                           Ref.: RFC 2327
   
      SDP_K         B00B       String     Encryption Key
   
                                           Ref.: RFC 2327
   
      SDP_A         B00C       String     Zero or more session
                                           attributes
   
                                           Ref.: RFC 2327
   
      SDP_T         B00D       String     Active Session Time
   
                                           Ref.: RFC 2327
   
      SDP_R         B00E       String     Zero or more repeat times
   
                                           Reference: RFC 2327
   
      SDP_M         B00F       String     Media type, port, transport
                                           and format
   
                                           Ref.: RFC 2327
   
   
   
   C.12  H.245
   
   
      PropertyID   Property   Type       Value
                    tag
   
      OLC          C001       Octet      The value of H.245
                                           OpenLogicalChannel
   
   
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      PropertyID   Property   Type       Value
                    tag
   
                               string     structure.
   
                                           Ref.: ITU-T H.245
   
      OLCack       C002       Octet      The value of H.245
                               string     OpenLogicalChannelAck
                                           structure.
   
                                           Ref.: ITU-T H.245
   
      OLCcnf       C003       Octet      The value of H.245
                               string     OpenLogicalChannelConfirm
                                           structure.
   
                                           Ref.: ITU-T H.245
   
      OLCrej       C004       Octet      The value of H.245
                               string     OpenLogicalChannelReject
                                           structure.
   
                                           Ref.: ITU-T H.245
   
      CLC          C005       Octet      The value of H.245
                               string     CloseLogicalChannel
                                           structure.
   
                                           Ref.: ITU-T H.245
   
      CLCack       C006       Octet      The value of H.245
                               string     CloseLogicalChannelAck
                                           structure.
   
                                           Ref.: ITU-T H.245
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
   ANNEX D  TRANSPORT OVER IP
   
   D.1   Transport over IP/UDP using Application Level Framing (ALF)
   
      Protocol messages defined in this Recommendation may be transmitted
      over UDP. When no port is provided by the peer (see 7.2.8), commands
      SHOULD be sent to the default port number: 2944 for text-encoded
      operation, or 2945 for binary-encoded operation. Responses must be
      sent to the address and port from which the corresponding commands
      were sent.
   
      ALF is a set of techniques that allows an application, as opposed to
      a stack, to affect how messages are sent to the other side. A typical
      ALF technique is to allow an application to change the order of
      messages sent when there is a queue after it has queued them.  There
      is no formal specification for ALF. The procedures in Annex D.1
      contain a minimum suggested set of ALF behaviours
   
      Implementors using IP/UDP with ALF SHOULD be aware of the
      restrictions of the MTU on the maximum message size.
   
   D.1.1 Providing At-Most-Once functionality
   
      Messages, being carried over UDP, may be subject to losses. In the
      absence of a timely response, commands are repeated. Most commands
      are not idempotent. The state of the MG would become unpredictable
      if, for example, Add commands were executed several times. The
      transmission procedures shall thus provide an "At-Most-Once"
      functionality.
   
      Peer protocol entities are expected to keep in memory a list of the
      responses that they sent to recent transactions and a list of the
      transactions that are currently outstanding. The transaction
      identifier of each incoming message is compared to the transaction
      identifiers of the recent responses sent to the same MId. If a match
      is found, the entity does not execute the transaction, but simply
      repeats the response. If no match is found, the message will be
      compared to the list of currently outstanding transactions. If a
      match is found in that list, indicating a duplicate transaction, the
      entity does not execute the transaction (see D.1.4 for procedures on
      sending TransactionPending).
   
      The procedure uses a long timer value, noted LONG-TIMER in the
      following. The timer SHOULD be set larger than the maximum duration
      of a transaction, which SHOULD take into account the maximum number
      of repetitions, the maximum value of the repetition timer and the
      maximum propagation delay of a packet in the network. A suggested
      value is 30 seconds.
   
   
   
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      The copy of the responses may be destroyed either LONG-TIMER seconds
      after the response is issued, or when the entity receives a
      confirmation that the response has been received, through the
      "Response Acknowledgement parameter". For transactions that are
      acknowledged through this parameter, the entity shall keep a copy of
      the transaction-id for LONG-TIMER seconds after the response is
      issued, in order to detect and ignore duplicate copies of the
      transaction request that could be produced by the network.
   
   D.1.2 Transaction identifiers and three-way handshake
   
   D.1.2.1  Transaction identifiers
   
      Transaction identifiers are 32-bit integer numbers. A Media Gateway
      Controller may decide to use a specific number space for each of the
      MGs that they manage, or to use the same number space for all MGs
      that belong to some arbitrary group. MGCs may decide to share the
      load of managing a large MG between several independent processes.
      These processes will share the same transaction number space. There
      are multiple possible implementations of this sharing, such as having
      a centralized allocation of transaction identifiers, or pre-
      allocating non-overlapping ranges of identifiers to different
      processes. The implementations shall guarantee that unique
      transaction identifiers are allocated to all transactions that
      originate from a logical MGC (identical mId). MGs can simply detect
      duplicate transactions by looking at the transaction identifier and
      mId only.
   
   D.1.2.2  Three-way handshake
   
      The TransactionResponse Acknowledgement parameter can be found in any
      message. It carries a set of "confirmed transaction-id ranges".
      Entities may choose to delete the copies of the responses to
      transactions whose id is included in "confirmed transaction-id
      ranges" received in the transaction response messages. They SHOULD
      silently discard further commands when the transaction-id falls
      within these ranges.
   
      The "confirmed transaction-id ranges" values shall not be used if
      more than LONG-TIMER seconds have elapsed since the MG issued its
      last response to that MGC, or when a MG resumes operation. In this
      situation, transactions SHOULD be accepted and processed, without any
      test on the transaction id.
   
      Messages that carry the "Transaction Response Acknowledgement"
      parameter may be transmitted in any order. The entity shall retain
      the "confirmed transaction-id ranges" receivedfor LONG-TIMER seconds.
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      In the binary encoding, if only the firstAck is present in a response
      acknowledgement (see A.2), only one transaction is acknowledged. If
      both firstAck and lastAck are present, then the range of transactions
      from firstAck to lastAck is acknowledged. In the text encoding, a
      horizontal dash is used to indicate a range of transactions being
      acknowledged (see B.2).
   
   D.1.3 Computing retransmission timers
   
      It is the responsibility of the requesting entity to provide suitable
      timeouts for all outstanding transactions, and to retry transactions
      when timeouts have been exceeded. Furthermore, when repeated
      transactions fail to be acknowledged, it is the responsibility of the
      requesting entity to seek redundant services and/or clear existing or
      pending connections.
   
      The specification purposely avoids specifying any value for the
      retransmission timers. These values are typically network dependent.
      The retransmission timers SHOULD normally estimate the timer value by
      measuring the time spent between the sending of a command and the
      return of a response. Implementations SHALL ensure that the algorithm
      used to calculate retransmission timing performs an exponentially
      increasing backoff of the retransmission timeout for each
      retransmission or repetition after the first one.
   
      NOTE - One possibility is to use the algorithm implemented in TCP-IP,
         which uses two variables:
   
      -  The average acknowledgement delay (AAD), estimated through an
         exponentially smoothed average of the observed delays.
   
      -  The average deviation (ADEV), estimated through an exponentially
         smoothed average of the absolute value of the difference between
         the observed delay and the current average. The retransmission
         timer, in TCP, is set to the sum of the average delay plus N times
         the average deviation. The maximum value of the timer SHOULD
         however be bounded for the protocol defined in this
         Recommendation, in order to guarantee that no repeated packet
         would be received by the gateways after LONG-TIMER seconds. A
         suggested maximum value is 4 seconds.
   
      After any retransmission, the entity SHOULD do the following:
   
      -  It SHOULD double the estimated value of the average delay, AAD.
   
      -  It SHOULD compute a random value, uniformly distributed between
         0.5 AAD and AAD.
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      -  It SHOULD set the retransmission timer to the sum of that random
         value and N times the average deviation.
   
      This procedure has two effects. Because it includes an exponentially
      increasing component, it will automatically slow down the stream of
      messages in case of congestion. Because it includes a random
      component, it will break the potential synchronization between
      notifications triggered by the same external event.
   
   D.1.4 Provisional responses
   
      Executing some transactions may require a long time. Long execution
      times may interact with the timer-based retransmission procedure.
      This may result either in an inordinate number of retransmissions, or
      in timer values that become too long to be efficient. Entities that
      can predict that a transaction will require a long execution time may
      send a provisional response, "Transaction Pending". They SHOULD send
      this response if they receive a repetition of a transaction that is
      still being executed.
   
      Entities that receive a Transaction Pending shall switch to a
      different repetition timer for repeating requests. The root
      Termination has a property (ProvisionalResponseTimerValue), which can
      be set to the requested maximum number of milliseconds between
      receipt of a command and transmission of the TransactionPending
      response. Upon receipt of a final response following receipt of
      provisional responses, an immediate confirmation shall be sent, and
      normal repetition timers shall be used thereafter. An entity that
      sends a provisional response, SHALL include the immAckRequired field
      in the ensuing final response, indicating that an immediate
      confirmation is expected. Receipt of a Transaction Pending after
      receipt of a reply shall be ignored.
   
   D.1.5 Repeating Requests, Responses and Acknowledgements
   
      The protocol is organized as a set of transactions, each of which is
      composed request and a response, commonly referred to as an
      acknowledgement. The protocol messages, being carried over UDP, may
      be subject to losses. In the absence of a timely response,
      transactions are repeated. Entities are expected to keep in memory a
      list of the responses that they sent to recent transactions, i.e. a
      list of all the responses they sent over the last LONG-TIMER seconds,
      and a list of the transactions that are currently being executed.
   
      The repetition mechanism is used to guard against three types of
      possible errors:
   
      -  transmission errors, when for example a packet is lost due to
         noise on a line or congestion in a queue;
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      -  component failure, when for example an interface to a entity
         becomes unavailable;
   
      -  entity failure, when for example an entire entity become
         unavailable.
   
      The entities SHOULD be able to derive from the past history an
      estimate of the packet loss rate due to transmission errors. In a
      properly configured system, this loss rate SHOULD be kept very low,
      typically less than 1%. If a Media Gateway Controller or a Media
      Gateway has to repeat a message more than a few times, it is very
      legitimate to assume that something else than a transmission error is
      occurring. For example, given a loss rate of 1%, the probability that
      five consecutive transmission attempts fail is 1 in 100 billion, an
      event that SHOULD occur less than once every 10 days for a Media
      Gateway Controller that processes 1000 transactions per second.
      (Indeed, the number of repetition that is considered excessive SHOULD
      be a function of the prevailing packet loss rate.) We SHOULD note
      that the "suspicion threshold", which we will call "Max1", is
      normally lower than the "disconnection threshold", which SHOULD be
      set to a larger value.
   
      A classic retransmission algorithm would simply count the number of
      successive repetitions, and conclude that the association is broken
      after retransmitting the packet an excessive number of times
      (typically between 7 and 11 times.) In order to account for the
      possibility of an undetected or in progress "failover", we modify the
      classic algorithm so that if the Media Gateway receives a valid
      ServiceChange message announcing a failover, it will start
      transmitting outstanding commands to that new MGC. Responses to
      commands are still transmitted to the source address of the command.
   
      In order to automatically adapt to network load, this Recommendation
      specifies exponentially increasing timers. If the initial timer is
      set to 200 milliseconds, the loss of a fifth retransmission will be
      detected after about 6 seconds. This is probably an acceptable
      waiting delay to detect a failover. The repetitions SHOULD continue
      after that delay not only in order to perhaps overcome a transient
      connectivity problem, but also in order to allow some more time for
      the execution of a failover  (waiting a total delay of 30 seconds is
      probably acceptable).
   
      It is, however, important that the maximum delay of retransmissions
      be bounded. Prior to any retransmission, it is checked that the time
      elapsed since the sending of the initial datagram is no greater than
      T-MAX. If more than T-MAX time has elapsed, the MG concludes that the
      MGC has failed, and it begins its recovery process as described in
      section 11.5. If the MG retries to connect to the current MGC it
      shall use a ServiceChange with ServiceChangeMethod set to
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      Disconnected so that the new MGC will be aware that the MG lost one
      or more transactions. The value T-MAX is related to the LONG-TIMER
      value: the LONG-TIMER value is obtained by adding to T MAX the
      maximum propagation delay in the network.
   
   D.2   Using TCP
   
      Protocol messages as defined in this Recommendation may be
      transmitted over TCP. When no port is specified by the other side
      (see 7.2.8), the commands SHOULD be sent to the default port. The
      defined protocol has messages as the unit of transfer, while TCP is a
      stream-oriented protocol. TPKT, according to RFC 1006, SHALL be used
      to delineate messages within the TCP stream.
   
      In a transaction-oriented protocol, there are still ways for
      transaction requests or responses to be lost. As such, it is
      recommended that entities using TCP transport implement application
      level timers for each request and each response, similar to those
      specified for application level framing over UDP.
   
   D.2.1 Providing the At-Most-Once functionality
   
      Messages, being carried over TCP, are not subject to transport
      losses, but loss of a transaction request or its reply may
      nonetheless be noted in real implementations. In the absence of a
      timely response, commands are repeated. Most commands are not
      idempotent. The state of the MG would become unpredictable if, for
      example, Add commands were executed several times.
   
      To guard against such losses, it is recommended that entities follow
      the procedures in D.1.1.
   
   D.2.2 Transaction identifiers and three-way handshake
   
      For the same reasons, it is possible that transaction replies may be
      lost even with a reliable delivery protocol such as TCP. It is
      recommended that entities follow the procedures in D.1.2.2.
   
   D.2.3 Computing retransmission timers
   
      With reliable delivery, the incidence of loss of a transaction
      request or reply is expected to be very low. Therefore, only simple
      timer mechanisms are required. Exponential back-off algorithms SHOULD
      not be necessary, although they could be employed where, as in an
      MGC, the code to do so is already required, since MGCs must implement
      ALF/UDP as well as TCP.
   
   
   
   
   
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   D.2.4 Provisional responses
   
      As with UDP, executing some transactions may require a long time.
      Entities that can predict that a transaction will require a long
      execution time may send a provisional response, "Transaction
      Pending". They SHOULD send this response if they receive a repetition
      of a transaction that is still being executed.
   
      Entities that receive a Transaction Pending shall switch to a longer
      repetition timer for that transaction.
   
      Entities shall retain Transactions and replies until they are
      confirmed. The basic procedure of D.1.4 SHOULD be followed, but
      simple timer values SHOULD be sufficient. There is no need to send an
      immediate confirmation upon receipt of a final response.
   
   D.2.5 Ordering of commands
   
      TCP provides ordered delivery of transactions. No special procedures
      are required. It SHOULD be noted that ALF/UDP allows sending entity
      to modify its behaviour under congestion, and in particular, could
      reorder transactions when congestion is encountered. TCP could not
      achieve the same results.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
   ANNEX E  BASIC PACKAGES
   
      This annex contains definitions of some packages for use with
      Recommendation H.248.1.
   
   E.1   Generic
   
      PackageID: g (0x0001)
      Version: 1
      Extends: None
   
      Description:
         Generic package for commonly encountered items
   
   E.1.1 Properties
   
      None
   
   E.1.2 Events
   
      Cause
   
         EventID: cause (0x0001)
   
         Generic error event
   
         EventsDescriptor parameters:  None
   
         ObservedEvents Descriptor Parameters:
   
            General Cause
   
               ParameterID: Generalcause (0x0001)
   
               This parameter groups the failures into six groups, which
               the MGC may act upon.
   
               Type: enumeration
   
               Possible values:
                     "NR" Normal Release (0x0001)
                     "UR" Unavailable Resources (0x0002)
                     "FT" Failure, Temporary (0x0003)
                     "FP" Failure, Permanent (0x0004)
                     "IW" Interworking Error (0x0005)
                     "UN" Unsupported (0x0006)
   
            Failure Cause
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
               ParameterID: Failurecause (0x0002)
   
               Possible values:  OCTET STRING
   
               Description: The Failure Cause is the value generated by the
               Released equipment, i.e. a released network connection. The
               concerned value is defined in the appropriate bearer control
               protocol.
   
   
      Signal Completion
   
         EventID: sc (0x0002)
   
         Indicates the termination of a signal for which the
         notifyCompletion parameter was set to enable reporting of a
         completion event. For further procedural description, see 7.1.1,
         7.1.17 and 7.2.7.
   
         EventsDescriptor parameters:  None
   
         ObservedEvents Descriptor parameters:
   
            Signal Identity
   
               ParameterID: SigID (0x0001)
   
               This parameter identifies the signal which has terminated.
               For a signal that is contained in a signal list, the signal
               list identity parameter SHOULD also be returned indicating
               the appropriate list.
   
               Type: Binary: octet (string), Text: string
   
               Possible values: a signal which has terminated. A signal
               shall be identified using the pkgdName syntax without
               wildcarding.
   
            Termination Method
   
               ParameterID: Meth (0x0002)
   
               Indicates the means by which the signal terminated.
   
               Type: enumeration
   
               Possible values:
                  "TO" (0x0001) Signal timed out or otherwise completed on
                                its own
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                  "EV" (0x0002) Interrupted by event
                  "SD" (0x0003) Halted by new Signals descriptor
                  "NC" (0x0004) Not completed, other cause
   
            Signal List ID
   
               ParameterID:  SLID (0x0003)
   
               Indicates to which signal list a signal belongs. The
               SignalList ID is only returned in cases where the signal
               resides in a signal list.
   
               Type: integer
   
               Possible values: any integer
   
   E.1.3 Signals
   
      None.
   
   E.1.4 Statistics
   
      None.
   
   
   
   E.2   Base Root Package
   
      Base Root Package
   
      PackageID: root (0x0002)
      Version: 2
      Extends: None
   
      Description:
   
      This package defines Gateway wide properties.
   
   E.2.1 Properties
   
      MaxNumberOfContexts
   
         PropertyID: maxNumberOfContexts (0x0001)
   
         The value of this property gives the maximum number of contexts
         that can exist at any time. The NULL context is not included in
         this number.
   
         Type: double
   
   
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                         Megaco Protocol version 2            April 2003
   
   
         Possible values: 1 and up
   
         Defined in: TerminationState
   
         Characteristics: read only
   
   
      MaxTerminationsPerContext
   
         PropertyID: maxTerminationsPerContext (0x0002)
   
         The maximum number of allowed terminations in a context, see 6.1
   
         Type: integer
   
         Possible values: any integer
   
         Defined in: TerminationState
   
         Characteristics: read only
   
   
      normalMGExecutionTime
   
         PropertyId: normalMGExecutionTime (0x0003)
   
         Settable by the MGC to indicate the interval within which the MGC
         expects a response to any transaction from the MG (exclusive of
         network delay)
   
         Type: integer
   
         Possible values: any integer, represents milliseconds
   
         Defined in: TerminationState
   
         Characteristics: read / write
   
   
      normalMGCExecutionTime
   
         PropertyId: normalMGCExecutionTime (0x0004)
   
         Settable by the MGC to indicate the interval within which the MG
         SHOULD expects a response to any transaction from the MGC
         (exclusive of network delay)
   
         Type: integer
   
   
   
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         Possible values: any integer, represents milliseconds
   
         Defined in: TerminationState
   
         Characteristics: read / write
   
   
      MGProvisionalResponseTimerValue
   
         PropertyId: MGProvisionalResponseTimerValue (0x0005)
   
         Indicates the time within which the MGC SHOULD expect a Pending
         Response from the MG if a Transaction cannot be completed.
         Initially set to normalMGExecutionTime plus network delay, but may
         be lowered.
   
         Type: Integer
   
         Possible Values: any integer, represents milliseconds
   
         Defined in: TerminationState
   
         Characteristics: read / write
   
   
      MGCProvisionalResponseTimerValue
   
         PropertyId: MGCProvisionalResponseTimerValue (0x0006)
   
         Indicates the time within which the MG SHOULD expect a Pending
         Response from the MGC if a Transaction cannot be completed.
         Initially set to normalMGCExecutionTime plus network delay, but
         may be lowered.
   
         Type: Integer
   
         Possible Values: any integer, represents milliseconds
   
         Defined in: TerminationState
   
         Characteristics: read / write
   
   
      MGCOriginatedPendingLimit
   
         PropertyId: MGCOriginatedPendingLimit (0x0007)
   
         Indicates the number of TransactionPendings that can be received
         from the MGC. Once this limit is exceeded the MGC SHOULD issue a
   
   
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         TransactionReply with Error 506   Number of TransactionPendings
         Exceeded, otherwise the MG can assume the Transaction to be in
         error.
   
         Type: Integer
   
         Possible Values: any possible integer
   
         Defined in: TerminationState
   
         Characteristics: Read/Write
   
   
      MGOriginatedPendingLimit
   
         PropertyId: MGOriginatedPendingLimit (0x0008)
   
         Indicates the number of TransactionPendings that can be received
         from the MG. Once this limit is exceeded the MG SHOULD issue a
         TransactionReply with Error 506   Number of TransactionPendings
         Exceeded, otherwise the MGC can assume the Transaction to be in
         error.
   
         Type: Integer
   
         Possible Values: any possible integer
   
         Defined in: TerminationState
   
         Characteristics: Read/Write
   
   E.2.2 Events
   
      None.
   
   E.2.3 Signals
   
      None.
   
   E.2.4 Statistics
   
      None.
   
   E.2.5 Procedures
   
      None.
   
   
   
   
   
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   E.3   Tone Generator Package
   
      PackageID: tonegen (0x0003)
      Version: 1
      Extends: None
   
      Description:
   
      This package defines signals to generate audio tones. This package
      does not specify parameter values. It is intended to be extendable.
      Generally, tones are defined as an individual signal with a
      parameter, ind, representing "interdigit" time delay, and a tone id
      to be used with playtones. A tone id SHOULD be kept consistent with
      any tone generation for the same tone. MGs are expected to be
      provisioned with the characteristics of appropriate tones for the
      country in which the MG is located.
   
      Designed to be extended only: Yes
   
   E.3.1 Properties
   
      None.
   
   E.3.2 Events
   
      None.
   
   E.3.3 Signals
   
      Play tone
   
         SignalID: pt (0x0001)
   
         Plays audio tone over an audio channel
   
         Signal Type: Brief
   
         Duration: Provisioned
   
         Additional parameters:
   
            Tone id list
   
               ParameterID: tl (0x0001)
   
               Type: list of tone ids
   
               List of tones to be played in sequence. The list SHALL
               contain one or more tone ids.
   
   
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            Inter signal duration
   
               ParameterID: ind (0x0002)
   
               Type: integer
   
               Timeout between two consecutive tones in milliseconds
   
      No tone ids are specified in this package. Packages that extend this
      package can add possible values for tone id as well as adding
      individual tone signals.
   
   E.3.4 Statistics
   
      None.
   
   E.3.5 Procedures
   
      None.
   
   
   
   E.4   Tone Detection Package
   
      PackageID: tonedet (0x0004)
      Version: 1
      Extends: None
   
      Designed to be extended only: Yes
   
      This Package defines events for audio tone detection. Tones are
      selected by name (tone id). MGs are expected to be provisioned with
      the characteristics of appropriate tones for the country in which the
      MG is located.
   
      This package does not specify parameter values. It is intended to be
      extendable.
   
   E.4.1 Properties
   
      None.
   
   E.4.2 Events
   
      Start tone detected
   
         EventID: std, 0x0001
   
   
   
   
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         Detects the start of a tone. The characteristics of positive tone
         detection are implementation dependent.
   
         EventsDescriptor parameters:
   
            Tone id list
   
               ParameterID: tl (0x0001)
   
               Type: list of tone ids
   
               Possible values: The only tone id defined in this package is
               "wild card" which is "*" in text encoding and 0x0000 in
               binary. Extensions to this package would add possible values
               for tone id. If tl is "wild card", any tone id is detected.
   
         ObservedEventsDescriptor parameters:
   
            Tone id
   
               ParameterID: tid (0x0003)
   
               Type: enumeration
   
               Possible values: "wildcard" as defined above is the only
               value defined in this package. Extensions to this package
               would add additional possible values for tone id.
   
   
      End tone detected
   
         EventID: etd, 0x0002
   
         Detects the end of a tone.
   
         EventDescriptor parameters:
   
            Tone id list
   
               ParameterID: tl (0x0001)
   
               Type: enumeration or list of enumerated types
   
               Possible values: No possible values are specified in this
               package. Extensions to this package would add possible
               values for tone id.
   
         ObservedEventsDescriptor parameters:
   
   
   
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            Tone id
   
               ParameterID: tid (0x0003)
   
               Type: enumeration
   
               Possible values: "wildcard" as defined above is the only
               value defined in this package. Extensions to this package
               would add possible values for tone id.
   
            Duration
   
               ParameterId: dur (0x0002)
   
               Type: integer, in milliseconds
   
               This parameter contains the duration of the tone from first
               detection until it stopped.
   
   
      Long tone detected
   
         EventID: ltd, 0x0003
   
         Detects that a tone has been playing for at least a certain amount
         of time
   
         EventDescriptor parameters:
   
            Tone id list
   
               ParameterID: tl (0x0001)
   
               Type: enumeration or list
   
               Possible values: "wildcard" as defined above is the only
               value defined in this package. Extensions to this package
               would add possible values for tone id.
   
            Duration:
   
               ParameterID: dur (0x0002)
   
               Type: integer, duration to test against
   
               Possible values: any legal integer, expressed in
               milliseconds
   
   
   
   
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         ObservedEventsDescriptor parameters:
   
            Tone id:
   
               ParameterID: tid (0x0003)
   
               Type: Enumeration
   
               Possible values: No possible values are specified in this
               package. Extensions to this package would add possible
               values for tone id.
   
   E.4.3 Signals
   
      None.
   
   E.4.4 Statistics
   
      None.
   
   E.4.5 Procedures
   
      None.
   
   
   
   E.5   Basic DTMF Generator Package
   
      PackageID: dg (0x0005)
      Version: 1
      Extends: tonegen version 1
   
      This package defines the basic DTMF tones as signals and extends the
      allowed values of parameter tl of playtone in tonegen.
   
   E.5.1 Properties
   
      None.
   
   E.5.2 Events
   
      None.
   
   E.5.3 Signals
   
      DTMF character 0
   
         SignalID: d0 (0x0010)
   
   
   
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         Generate DTMF 0 tone. The physical characteristic of DTMF 0 is
         defined in the gateway.
   
         Signal Type: Brief
   
         Duration: Provisioned
   
         Additional parameters:
   
            None
   
         Additional values:
   
            d0 (0x0010) is defined as a tone id for playtone
   
            The other DTMF characters are specified in exactly the same
            way. A table with all signal names and signal IDs is included.
            Note that each DTMF character is defined as both a signal and a
            tone id, thus extending the basic tone generation package. Also
            note that DTMF SignalIds are different from the names used in a
            digit map.
   
                     Signal name          Signal ID/Tone id
   
                     DTMF character 0     d0 (0x0010)
                     DTMF character 1     d1 (0x0011)
                     DTMF character 2     d2 (0x0012)
                     DTMF character 3     d3 (0x0013)
                     DTMF character 4     d4 (0x0014)
                     DTMF character 5     d5 (0x0015)
                     DTMF character 6     d6 (0x0016)
                     DTMF character 7     d7 (0x0017)
                     DTMF character 8     d8 (0x0018)
                     DTMF character 9     d9 (0x0019)
                     DTMF character *     ds (0x0020)
                     DTMF character #     do (0x0021)
                     DTMF character A     da (0x001a)
                     DTMF character B     db (0x001b)
                     DTMF character C     dc (0x001c)
                     DTMF character D     dd (0x001d)
   
   E.5.4 Statistics
   
      None.
   
   E.5.5 Procedures
   
      None.
   
   
   
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   E.6   DTMF detection Package
   
      PackageID: dd (0x0006)
      Version: 1
      Extends: tonedet version 1
   
      This package defines the basic DTMF tones detection. This Package
      extends the possible values of tone id in the "start tone detected"
      "end tone detected" and "long tone detected" events.
   
      Additional tone id values are all tone ids described in package dg
      (basic DTMF generator package).
   
      The following table maps DTMF events to digit map symbols as
      described in 7.1.14.
   
                       DTMF    Event Symbol
   
                       d0      "0"
                       d1      "1"
                       d2      "2"
                       d3      "3"
                       d4      "4"
                       d5      "5"
                       d6      "6"
                       d7      "7"
                       d8      "8"
                       d9      "9"
                       da      "A" or "a"
                       db      "B" or "b"
                       dc      "C" or "c"
                       dd      "D" or "d"
                       ds      "E" or "e"
                       do      "F" or "f"
   
   
   E.6.1 Properties
   
      None.
   
   E.6.2 Events
   
      DTMF digits
   
      EventIds are defined with the same names as the SignalIds defined in
      the table found in E.5.3.
   
   
   
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      DigitMap Completion Event
   
         EventID: ce, 0x0004
   
         Generated when a digit map completes as described in 7.1.14.
   
         EventsDescriptor parameters: None.
   
         ObservedEventsDescriptor parameters:
   
            DigitString
   
               ParameterID: ds (0x0001)
   
               Type: string of digit map symbols (possibly empty) returned
               as a quotedString
   
               Possible values: a sequence of the characters "0" through
               "9", "A" through "F", and the long duration modifier "Z".
   
               Description: the portion of the current dial string as
               described in 7.1.14 which matched part or all of an
               alternative event sequence specified in the digit map.
   
            Termination Method
   
               ParameterID: Meth (0x0003)
   
               Type: enumeration
   
               Possible values:
   
               "UM" (0x0001) Unambiguous match
   
               "PM" (0x0002) Partial match, completion by timer expiry or
               unmatched event
   
               "FM" (0x0003) Full match, completion by timer expiry or
               unmatched event
   
               Description: indicates the reason for generation of the
               event. See the procedures in 7.1.14.
   
   E.6.3 Signals
   
      None.
   
   
   
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   E.6.4 Statistics
   
      None.
   
   E.6.5 Procedures
   
      Digit map processing is activated only if an events descriptor is
      activated that contains a digit map completion event as defined in
      Section E.6.2 and that digit map completion event contains an eventDM
      field in the requested actions as defined in Section 7.1.9.  Other
      parameters such as KeepActive or embedded events of signals
      descriptors may also be present in the events descriptor and do not
      affect the activation of digit map processing.
   
   
   
   E.7   Call Progress Tones Generator Package
   
      PackageID: cg, 0x0007
      Version: 1
      Extends: tonegen version 1
   
      This package defines the basic call progress tones as signals and
      extends the allowed values of the tl parameter of playtone in
      tonegen.
   
   E.7.1 Properties
   
      None.
   
   E.7.2 Events
   
      None.
   
   E.7.3 Signals
   
      Dial Tone
   
         SignalID: dt (0x0030)
   
         Generate dial tone. The physical characteristic of dial tone is
         available in the gateway.
   
         Signal Type: TimeOut
   
         Duration: Provisioned
   
         Additional parameters:
   
   
   
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            None
   
         Additional values:
   
            dt (0x0030) is defined as a tone id for playtone
   
      The other tones of this package are defined in exactly the same way.
      A table with all signal names and signal IDs is included. Note that
      each tone is defined as both a signal and a tone id, thus extending
      the basic tone generation package.
   
             Signal Name                   Signal ID/tone id
   
             Dial Tone                     dt (0x0030)
   
             Ringing Tone                  rt (0x0031)
   
             Busy Tone                     bt (0x0032)
   
             Congestion Tone               ct (0x0033)
   
             Special Information Tone      sit(0x0034)
   
             (Recording) Warning Tone      wt (0x0035)
   
             Payphone Recognition Tone     prt (0x0036)
   
             Call Waiting Tone             cw (0x0037)
   
             Caller Waiting Tone           cr (0x0038)
   
   
   
   E.7.4 Statistics
   
      None.
   
   E.7.5 Procedures
   
      NOTE - The required set of tone ids corresponds to those defined in
      Recommendation E.180/Q.35. See Recommendation E.180/Q.35 for
      definition of the meanings of these tones.
   
   
   
   E.8   Call Progress Tones Detection Package
   
      PackageID: cd (0x0008)
      Version: 1
   
   
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      Extends: tonedet version 1
   
      This package defines the basic call progress detection tones. This
      package extends the possible values of tone id in the "start tone
      detected", "end tone detected" and "long tone detected" events.
   
      Additional values
   
         tone id values are defined for start tone detected, end tone
         detected and long tone detected with the same values as those in
         package cg (call progress tones generation package).
   
         The required set of tone ids corresponds to Recommendation
         E.180/Q.35. See Recommendation E.180/Q.35 for definition of the
         meanings of these tones.
   
   E.8.1 Properties
   
      None.
   
   E.8.2 Events
   
      Events are defined as in the call progress tones generator package
      (cg) for the tones listed in the table of E.7.3.
   
   E.8.3 Signals
   
      None.
   
   E.8.4 Statistics
   
      None.
   
   E.8.5 Procedures
   
      None.
   
   
   
   E.9   Analog Line Supervision Package
   
      PackageID: al, 0x0009
      Version: 1
      Extends: None
   
      This package defines events and signals for an analog line.
   
   
   
   
   
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   E.9.1 Properties
   
      None
   
   E.9.2 Events
   
      onhook
   
         EventID: on (0x0004)
   
         Detects handset going on hook. Whenever an events descriptor is
         activated that requests monitoring for an on-hook event and the
         line is already on-hook, then the MG shall behave according to the
         setting of the "strict" parameter.
   
         EventDescriptor parameters
   
            Strict Transition
            ParameterID: strict (0x0001)
   
            Type: enumeration
   
            Possible values:
   
               "exact" (0x00): only an actual hook state transition to on-
               hook is to be recognized;
   
               "state" (0x01): the event is to be recognized either if the
               hook state transition is detected or if the hook state is
               already on-hook;
   
               "failWrong" (0x02): if the hook state is already on-hook,
               the command fails and an error is reported.
   
         ObservedEventsDescriptor parameters
   
            Initial State
            ParameterID: init (0x0002)
   
            Type: Boolean
   
            Possible values:
   
               "True" means that the event was reported because the line
               was already on-hook when the events descriptor containing
               this event was activated;
   
               "False" means that the event represents an actual state
               transition to on-hook.
   
   
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      offhook
   
         EventID: of (0x0005)
   
         Detects handset going off hook. Whenever an events descriptor is
         activated that requests monitoring for an off-hook event and the
         line is already off-hook, then the MG shall behave according to
         the setting of the "strict" parameter.
   
         EventDescriptor parameters
   
            Strict Transition
            ParameterID: strict (0x0001)
   
            Type: enumeration
   
            Possible values:
   
               "exact" (0x00): only an actual hook state transition to off-
               hook is to be recognized;
   
               "state" (0x01): the event is to be recognized either if the
               hook state transition is detected or if the hook state is
               already off-hook;
   
               "failWrong" (0x02): if the hook state is already off-hook,
               the command fails and an error is reported.
   
         ObservedEventsDescriptor parameters
   
            Initial State
            ParameterID: init (0x0002)
   
            Type: Boolean
   
            Possible values:
   
               "True" means that the event was reported because the line
               was already off-hook when the events descriptor containing
               this event was activated;
   
               "False" means that the event represents an actual state
               transition to off-hook.
   
   
   
      flashhook
   
   
   
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         EventID: fl, 0x0006
   
         Detects handset flash. A flash occurs when an onhook is followed
         by an offhook between a minimum and maximum duration.
   
         EventDescriptor parameters
   
            Minimum duration
   
               ParameterID: mindur (0x0004)
   
               Type: integer in milliseconds
   
               Default value is provisioned.
   
            Maximum duration
   
               ParameterID: maxdur (0x0005)
   
               Type: integer in milliseconds
   
               Default value is provisioned.
   
         ObservedEventsDescriptor parameters
   
            None
   
   E.9.3 Signals
   
      ring
   
         SignalID: ri, 0x0002
   
         Applies ringing on the line
   
         Signal Type: TimeOut
   
         Duration: Provisioned
   
         Additional parameters:
   
            Cadence
   
               ParameterID: cad (0x0006)
   
               Type: list of integers representing durations of alternating
               on and off segments, constituting a complete ringing cycle
               starting with an on. Units in milliseconds
   
   
   
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               Default is fixed or provisioned. Restricted function MGs may
               ignore cadence values they are incapable of generating.
   
            Frequency
   
               ParameterID: freq (0x0007)
   
               Type: integer in Hz
   
               Default is fixed or provisioned. Restricted function MGs may
               ignore frequency values they are incapable of generating.
   
   E.9.4 Statistics
   
      None
   
   E.9.5 Procedures
   
      If the MGC sets an EventsDescriptor containing a hook state
      transition event (on-hook or off-hook) with the "strict" (0x0001)
      parameter set to "failWrong", and the hook state is already what the
      transition implies, the execution of the command containing that
      EventsDescriptor fails. The MG SHALL include error code 540
      "Unexpected initial hook state" in its reponse.
   
   E.9.6 Error code
   
      This package defines a new error code:
   
      540 - Unexpected initial hook state
   
      The procedure for use of this code is given in E.9.5.
   
   
   
   E.10  Basic Continuity Package
   
      PackageID: ct (0x000a)
      Version: 1
      Extends: None
   
      This package defines events and signals for continuity test. The
      continuity test includes provision of either a loopback or
      transceiver functionality.
   
   E.10.1   Properties
   
      None.
   
   
   
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   E.10.2   Events
   
      Completion
   
         EventID: cmp, 0x0005
   
         This event detects test completion of continuity test.
   
         EventDescriptor parameters
   
            None
   
         ObservedEventsDescriptor parameters
   
            Result
   
               ParameterID: res (0x0008)
   
               Type: enumeration
   
               Possible values: success (0x0001), failure (0x0000)
   
   E.10.3   Signals
   
      Continuity test
   
         SignalID: ct (0x0003)
   
         Initiates sending of continuity test tone on the termination to
         which it is applied.
   
         Signal Type: TimeOut
   
         Default value is provisioned
   
         Additional parameters:
   
            None
   
   
      Respond
   
         SignalID: rsp (0x0004)
   
         The signal is used to respond to a continuity test. See E.10.5 for
         further explanation.
   
         Signal Type: On/Off
   
   
   
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         Default duration is provisioned
   
         Additional parameters:
   
            None
   
   E.10.4   Statistics
   
      None.
   
   E.10.5   Procedures
   
      When a MGC wants to initiate a continuity test, it sends a command to
      the MG containing:
   
      -  a signals descriptor with the ct signal; and
   
      -  an events descriptor containing the cmp event.
   
      Upon reception of a command containing the ct signal and cmp event,
      the MG initiates the continuity test tone for the specified
      Termination. If the return tone is detected and any other required
      conditions are satisfied before the signal times out, the cmp event
      shall be generated with the value of the result parameter equal to
      success. In all other cases, the cmp event shall be generated with
      the value of the result parameter equal to failure.
   
      When a MGC wants the MG to respond to a continuity test, it sends a
      command to the MG containing a signals descriptor with the rsp
      signal. Upon reception of a command with the rsp signal, the MG
      either applies a loopback or (for 2-wire circuits) awaits reception
      of a continuity test tone. In the loopback case, any incoming
      information shall be reflected back as outgoing information. In the
      2-wire case, any time the appropriate test tone is received, the
      appropriate response tone SHOULD be sent. The MGC determines when to
      remove the rsp signal.
   
      When a continuity test is performed on a Termination, no echo devices
      or codecs shall be active on that Termination.
   
      Performing voice path assurance as part of continuity testing is
      provisioned by bilateral agreement between network operators.
   
      (Informative Note) Example tones and test procedure details are given
      in Q.724 sections 7 and 8, Q.764 section 2.1.8 and Q.1902.4.
   
   
   
   
   
   
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   E.11  Network Package
   
      PackageID: nt (0x000b)
      Version: 1
      Extends: None
   
      This package defines properties of network terminations independent
      of network type.
   
   E.11.1   Properties
   
      Maximum Jitter Buffer
   
         PropertyID: jit (0x0007)
   
         This property puts a maximum size on the jitter buffer.
   
         Type: integer in milliseconds
   
         Possible values: This property is specified in milliseconds.
   
         Defined in: LocalControlDescriptor
   
         Characteristics: read/write
   
   E.11.2   Events
   
      network failure
   
         EventID: netfail, 0x0005
   
         The termination generates this event upon detection of a failure
         due to external or internal network reasons.
   
         EventDescriptor parameters
   
            None
   
         ObservedEventsDescriptor parameters
   
            cause
   
               ParameterID: cs (0x0001)
   
               Type: string
   
               Possible values: any text string
   
   
   
   
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               This parameter may be included with the failure event to
               provide diagnostic information on the reason of failure.
   
   
      quality alert
   
         EventID: qualert, 0x0006
   
         This event allows the MG to indicate a loss of quality of the
         network connection. The MG may do this by measuring packet loss,
         interarrival jitter, propogation delay and then indicating this
         using a percentage of quality loss.
   
         EventDescriptor parameters
   
            Threshold
   
               ParameterId: th (0x0001)
   
               Type: integer
   
               Possible values: 0 to 99
   
               Description: threshold for percent of quality loss measured,
               calculated based on a provisioned method, that could take
               into consideration packet loss, jitter, and delay for
               example. Event is triggered when calculation exceeds the
               threshold.
   
         ObservedEventsDescriptor parameters
   
            Threshold
   
               ParameterId: th (0x0001)
   
               Type: integer
   
               Possible values: 0 to 99
   
               Description: percent of quality loss measured, calculated
               based on a provisioned method, that could take into
               consideration packet loss, jitter, and delay for example.
   
   E.11.3   Signals
   
      None.
   
   E.11.4   Statistics
   
   
   
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      Duration
   
         StatisticsID: dur (0x0001)
   
         Description: provides duration of time the termination has been in
         the Context.
   
         Type: double, in milliseconds
   
      Octets Sent
   
         StatisticID: os (0x0002)
   
         Type: double
   
         Possible values: any 64-bit integer
   
      Octets Received
   
         StatisticID: or (0x0003)
   
         Type: double
   
         Possible values: any 64-bit integer
   
   E.11.5   Procedures
   
      None.
   
   
   
   E.12  RTP Package
   
      PackageID: rtp (0x000c)
      Version: 1
      Extends: Network Package version 1
   
      This package is used to support packet-based multimedia data transfer
      by means of the Real-time Transport Protocol (RTP) [RFC 1889].
   
   E.12.1   Properties
   
      None.
   
   E.12.2   Events
   
      Payload Transition
   
         EventID: pltrans, 0x0001
   
   
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         This event detects and notifies when there is a transition of the
         RTP payload format from one format to another.
   
         EventDescriptor parameters
   
            None
   
         ObservedEventsDescriptor parameters
   
            ParameterName: rtppayload
   
            ParameterID: rtppltype, 0x01
   
            Type: list of enumerated types.
   
            Possible values: The encoding method shall be specified by
            using one or several valid encoding names, as defined in the
            RTP AV Profile or registered with IANA.
   
   E.12.3   Signals
   
      None.
   
   E.12.4   Statistics
   
      Packets Sent
   
         StatisticID: ps (0x0004)
   
         Type: double
   
         Possible values: any 64-bit integer
   
      Packets Received
   
         StatisticID: pr (0x0005)
   
         Type: double
   
         Possible values: any 64-bit integer
   
      Packet Loss
   
         StatisticID: pl (0x0006)
   
         Describes the current rate of packet loss on an RTP stream, as
         defined in IETF RFC 1889. Packet loss is expressed as percentage
         value: number of packets lost in the interval between two
   
   
   
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         reception reports, divided by the number of packets expected
         during that interval.
   
         Type: double
   
         Possible values: a 32-bit whole number and a 32-bit fraction.
   
      Jitter
   
         StatisticID: jit (0x0007)
   
         Requests the current value of the interarrival jitter on an RTP
         stream as defined in IETF RFC 1889. Jitter measures the variation
         in interarrival time for RTP data packets.
   
      Delay
   
         StatisticID:delay (0x0008)
   
         Requests the current value of packet propagation delay expressed
         in timestamp units. Same as average latency.
   
   E.12.5   Procedures
   
      None.
   
   
   
   E.13  TDM Circuit Package
   
      PackageID: tdmc (0x000d)
      Version: 1
      Extends: Network Package version 1
   
      This package may be used by any termination that supports gain and
      echo control.  It was originally intended for use on TDM circuits but
      may be more widely used.
   
      New versions or extensions of this package SHOULD take non-TDM use
      into account.
   
   E.13.1   Properties
   
      Echo Cancellation
   
         PropertyID: ec (0x0008)
   
         Type: boolean
   
   
   
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         Possible values:
   
            "on" (when the echo cancellation is requested) and
   
            "off" (when it is turned off.)
   
            The default is provisioned.
   
            Defined in: LocalControlDescriptor
   
            Characteristics: read/write
   
      Gain Control
   
         PropertyID: gain (0x000a)
   
         Gain control, or usage of of signal level adaptation and noise
         level reduction is used to adapt the level of the signal. However,
         it is necessary, for example for modem calls, to turn off this
         function.
   
         Type: integer
   
         Possible values:
   
            The gain control parameter may either be specified as
            "automatic" (0xffffffff), or as an explicit number of decibels
            of gain (any other integer value). The default is provisioned
            in the MG.
   
         Defined in: LocalControlDescriptor
   
         Characteristics: read/write
   
   E.13.2   Events
   
      None.
   
   E.13.3   Signals
   
      None.
   
   E.13.4   Statistics
      None.
   
   E.13.5   Procedures
      None.
   
   
   
   
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   APPENDIX I  Example Call Flows
   
      All H.248.1 implementors must read the normative part of this
      document carefully before implementing from it. No one SHOULD use the
      examples in this appendix as stand-alone explanations of how to
      create protocol messages.
   
      The examples in this appendix use SDP for encoding of the Local and
      Remote stream descriptors. SDP is defined in RFC 2327. If there is
      any discrepancy between the SDP in the examples, and RFC 2327, the
      RFC SHOULD be consulted for correctness. Audio profiles used are
      those defined in RFC 1890, and others registered with IANA. For
      example, G.711 A-law is called PCMA in SDP, and is assigned profile
      0. G.723.1 is called G723 and is profile 4; H.263 is called H263 and
      is profile 34. See also http://www.iana.org/assignments/rtp-
      parameters.
   
   I.1   Residential Gateway to Residential Gateway Call
   
      This example scenario illustrates the use of the elements of the
      protocol to set up a Residential Gateway to Residential Gateway call
      over an IP-based network. For simplicity, this example assumes that
      both Residential Gateways involved in the call are controlled by the
      same Media Gateway Controller.
   
   I.1.1 Programming Residential GW Analog Line Terminations for Idle
         Behaviour
   
      The following illustrates the API invocations from the Media Gateway
      Controller and Media Gateways to get the Terminations in this
      scenario programmed for idle behaviour. Both the originating and
      terminating Media Gateways have idle AnalogLine Terminations
      programmed to look for call initiation events (i.e. offhook) by using
      the Modify Command with the appropriate parameters. The null Context
      is used to indicate that the Terminations are not yet involved in a
      Context. The ROOT termination is used to indicate the entire MG
      instead of a termination within the MG.
   
      In this example, MG1 has the IP address 124.124.124.222, MG2 is
      125.125.125.111, and the MGC is 123.123.123.4. The default Megaco
      port is 55555 for all three.
   
      1) An MG registers with an MGC using the ServiceChange command:
   
      MG1 to MGC:
   
      MEGACO/1 [124.124.124.222]
      Transaction = 9998 {
          Context = - {
   
   
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              ServiceChange = ROOT {Services {
                  Method=Restart,
                  ServiceChangeAddress=55555, Profile=ResGW/1}
              }
          }
      }
   
      2) The MGC sends a reply:
   
      MGC to MG1:
   
      MEGACO/1 [123.123.123.4]:55555
      Reply = 9998 {
         Context = - {ServiceChange = ROOT {
           Services {ServiceChangeAddress=55555, Profile=ResGW/1} } }
      }
   
      3) The MGC programs a Termination in the NULL context. The
      terminationId is A4444, the streamId is 1, the requestId in the
      Events descriptor is 2222. The mId is the identifier of the sender of
      this message, in this case, it is the IP address and port
      [123.123.123.4]:55555. Mode for this stream is set to SendReceive.
      "al" is the analog line supervision package. Local and Remote are
      assumed to be provisioned.
   
      MGC to MG1:
   
      MEGACO/1 [123.123.123.4]:55555
      Transaction = 9999 {
          Context = - {
              Modify = A4444 {
                  Media { Stream = 1 {
                           LocalControl {
                               Mode = SendReceive,
                               tdmc/gain=2,  ; in dB,
                               tdmc/ec=on
                                        },
                                     }
                        },
                  Events = 2222 {al/of (strict=state)}
              }
          }
      }
   
      The dialplan script could have been loaded into the MG previously.
      Its function would be to wait for the OffHook, turn on dialtone and
      start collecting DTMF digits. However in this example, we use the
      digit map, which is put into place after the offhook is detected
      (step 5 below).
   
   
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      Note that the embedded EventsDescriptor could have been used to
      combine steps 3 and 4 with steps 8 and 9, eliminating steps 6 and 7.
   
      4) The MG1 accepts the Modify with this reply:
   
      MG1 to MGC:
   
      MEGACO/1 [124.124.124.222]:55555
      Reply = 9999 {
         Context = - {Modify = A4444}
      }
   
      5) A similar exchange happens between MG2 and the MGC, resulting in
      an idle Termination called A5555.
   
   I.1.2 Collecting Originator Digits and Initiating Termination
   
      The following builds upon the previously shown conditions. It
      illustrates the transactions from the Media Gateway Controller and
      originating Media Gateway (MG1) to get the originating Termination
      (A4444) through the stages of digit collection required to initiate a
      connection to the terminating Media Gateway (MG2).
   
      6) MG1 detects an offhook event from User 1 and reports it to the
      Media Gateway Controller via the Notify Command.
   
      MG1 to MGC:
   
      MEGACO/1 [124.124.124.222]:55555
      Transaction = 10000 {
         Context = - {
             Notify = A4444 {ObservedEvents =2222 {
               19990729T22000000:al/of(init=false)}}
         }
      }
   
      7) And the Notify is acknowledged.
   
      MGC to MG1:
   
      MEGACO/1 [123.123.123.4]:55555
      Reply = 10000 {
          Context = - {Notify = A4444}
      }
   
      8) The MGC Modifies the Termination to play dial tone, to look for
      digits according to Dialplan0 and to look for the on-hook event now.
   
      MGC to MG1:
   
   
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      MEGACO/1 [123.123.123.4]:55555
      Transaction = 10001 {
          Context = - {
              Modify = A4444 {
                  Events = 2223 {
                      al/on(strict=state), dd/ce {DigitMap=Dialplan0}
                  },
                  Signals {cg/dt},
                  DigitMap= Dialplan0{
      (0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)}
              }
          }
      }
   
      9) And the Modify is acknowledged.
   
      MG1 to MGC:
   
      MEGACO/1 [124.124.124.222]:55555
      Reply = 10001 {
          Context = - {Modify = A4444}
      }
   
      10)   Next, digits are accumulated by MG1 as they are dialed by User
      1.  Dialtone is stopped upon detection of the first digit. When an
      appropriate match is made of collected digits against the currently
      programmed Dialplan for A4444, another Notify is sent to the Media
      Gateway Controller.
   
      MG1 to MGC:
   
      MEGACO/1 [124.124.124.222]:55555
      Transaction = 10002 {
         Context = - {
             Notify = A4444 {ObservedEvents =2223 {
               19990729T22010001:dd/ce{ds="916135551212",Meth=UM}}}
         }
      }
   
      11)   And the Notify is acknowledged.
   
      MGC to MG1:
   
      MEGACO/1 [123.123.123.4]:55555
      Reply = 10002 {
          Context = - {Notify = A4444}
      }
   
   
   
   
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      12)   The controller then analyses the digits and determines that a
      connection needs to be made from MG1 to MG2. Both the TDM termination
      A4444, and an RTP termination are added to a new Context in MG1. Mode
      is ReceiveOnly since Remote descriptor values are not yet specified.
      Preferred codecs are in the MGC's preferred order of choice.
   
      MGC to MG1:
   
      MEGACO/1 [123.123.123.4]:55555
      Transaction = 10003 {
          Context = $ {
             Add = A4444,
             Add = $ {
                 Media {
                   Stream = 1 {
                        LocalControl {
                            Mode = ReceiveOnly,
   
                            nt/jit=40 ; in ms
                        },
                        Local {
      v=0
      c=IN IP4 $
      m=audio $ RTP/AVP 4
      a=ptime:30
      v=0
      c=IN IP4 $
      m=audio $ RTP/AVP 0
                        }
                   }
                }
             }
          }
      }
   
      NOTE - The MGC states its preferred parameter values as a series of
      SDP blocks in Local. The MG fills in the Local descriptor in the
      Reply.
   
      13)   MG1 acknowledges the new Termination and fills in the Local IP
      address and UDP port. It also makes a choice for the codec based on
      the MGC preferences in Local. MG1 sets the RTP port to 2222.
   
      MG1->MGC:
   
      MEGACO/1 [124.124.124.222]:55555
      Reply = 10003 {
         Context = 2000 {
            Add = A4444,
   
   
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            Add=A4445{
               Media {
                   Stream = 1 {
                       Local {
      v=0
      o=- 2890844526 2890842807 IN IP4 124.124.124.222
      s=-
      t= 00
      c=IN IP4 124.124.124.222
      m=audio 2222 RTP/AVP 4
      a=ptime:30
      a=recvonly
                       } ; RTP profile for G.723.1 is 4
                   }
               }
            }
         }
      }
   
      14)   The MGC will now associate A5555 with a new Context on MG2, and
      establish an RTP Stream (i.e. A5556 will be assigned), SendReceive
      connection through to the originating user, User 1. The MGC also sets
      ring on A5555.
   
      MGC to MG2:
   
      MEGACO/1 [123.123.123.4]:55555
      Transaction = 50003 {
          Context = $ {
             Add = A5555  { Media {
                  Stream = 1 {
                       LocalControl {Mode = SendReceive} }},
            Events=1234{al/of(strict=state)},
                  Signals {al/ri}
                  },
             Add  = $ {Media {
                  Stream = 1 {
                       LocalControl {
                          Mode = SendReceive,
                          nt/jit=40 ; in ms
                       },
                       Local {
      v=0
      c=IN IP4 $
      m=audio $ RTP/AVP 4
      a=ptime:30
                       },
                       Remote {
      v=0
   
   
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      c=IN IP4 124.124.124.222
      m=audio 2222 RTP/AVP 4
      a=ptime:30
                       } ; RTP profile for G.723.1 is 4
                   }
                }
            }
         }
      }
   
      15)   This is acknowledged. The stream port number is different from
      the control port number. In this case it is 1111 (in SDP).
   
      MG2 to MGC:
   
      MEGACO/1 [125.125.125.111]:55555
      Reply = 50003 {
         Context = 5000 {
         Add = A5555,
            Add = A5556{
               Media {
                  Stream = 1 {
                      Local {
      v=0
      o=- 7736844526 7736842807 IN IP4 125.125.125.111
      s=-
      t= 00
      c=IN IP4 125.125.125.111
      m=audio 1111 RTP/AVP 4
      }
                  } ; RTP profile for G.723.1 is 4
               }
             }
         }
      }
   
      16)   The above IPAddr and UDPport need to be given to MG1 now.
   
      MGC to MG1:
   
      MEGACO/1 [123.123.123.4]:55555
      Transaction = 10005 {
        Context = 2000 {
          Modify = A4444 {
            Signals {cg/rt}
          },
          Modify = A4445 {
             Media {
                  Stream = 1 {
   
   
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                      Remote {
      v=0
      o=- 7736844526 7736842807 IN IP4 125.125.125.111
      s=-
      t= 00
      c=IN IP4 125.125.125.111
      m=audio 1111 RTP/AVP 4
                      }
                  } ; RTP profile for G.723.1 is 4
              }
          }
        }
      }
   
      MG1 to MGC:
   
      MEGACO/1 [124.124.124.222]:55555
      Reply = 10005 {
         Context = 2000 {Modify = A4444, Modify = A4445}
      }
   
      17)   The two gateways are now connected and User 1 hears the
      RingBack. The MG2 now waits until User2 picks up the receiver and
      then the two-way call is established.
   
      From MG2 to MGC:
   
      MEGACO/1 [125.125.125.111]:55555
      Transaction = 50005 {
         Context = 5000 {
             Notify = A5555 {ObservedEvents =1234 {
               19990729T22020002:al/of(init=false)}}
         }
      }
   
      From MGC to MG2:
   
      MEGACO/1 [123.123.123.4]:55555
      Reply = 50005 {
          Context = - {Notify = A5555}
      }
   
      From MGC to MG2:
   
      MEGACO/1 [123.123.123.4]:55555
      Transaction = 50006 {
         Context = 5000 {
            Modify = A5555 {
               Events = 1235 {al/on(strict=state)},
   
   
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               Signals { } ; to turn off ringing
            }
         }
      }
   
      From MG2 to MGC:
   
      MEGACO/1 [125.125.125.111]:55555
      Reply = 50006 {
       Context = 5000 {Modify = A4445}
      }
   
      18)   Change mode on MG1 to SendReceive, and stop the ringback.
   
      MGC to MG1:
   
      MEGACO/1 [123.123.123.4]:55555
      Transaction = 10006 {
         Context = 2000 {
            Modify = A4445 {
               Media {
                  Stream = 1 {
                     LocalControl {
                        Mode=SendReceive
                     }
                  }
               }
            },
            Modify = A4444 {
               Signals { }
            }
         }
      }
   
      from MG1 to MGC:
   
      MEGACO/1 [124.124.124.222]:55555
      Reply = 10006 {
         Context = 2000 {Modify = A4445, Modify = A4444}}
   
      19)   The MGC decides to Audit the RTP termination on MG2.
   
      MEGACO/1 [123.123.123.4]:55555
      Transaction = 50007 {
         Context = - {AuditValue = A5556{
            Audit{Media, DigitMap, Events, Signals, Packages, Statistics }}
         }
      }
   
   
   
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      20)   The MG2 replies.
   
      MEGACO/1 [125.125.125.111]:55555
      Reply = 50007 {
         Context = - {
            AuditValue = A5556 {
                Media {
                   TerminationState { ServiceStates = InService,
                 Buffer = OFF },
                Stream = 1 {
                       LocalControl { Mode = SendReceive,
                          nt/jit=40 },
                       Local {
      v=0
      o=- 7736844526 7736842807 IN IP4 125.125.125.111
      s=-
      t= 00
      c=IN IP4 125.125.125.111
      m=audio 1111 RTP/AVP  4
      a=ptime:30
                      },
                       Remote {
      v=0
      o=- 2890844526 2890842807 IN IP4 124.124.124.222
      s=-
      t= 00
      c=IN IP4 124.124.124.222
      m=audio 2222 RTP/AVP  4
      a=ptime:30
                       } } },
                Events,
             Signals,
             DigitMap,
             Packages {nt-1, rtp-1},
                Statistics { rtp/ps=1200,  ; packets sent
                             nt/os=62300, ; octets sent
                             rtp/pr=700, ; packets received
                             nt/or=45100, ; octets received
                             rtp/pl=0.2,  ; % packet loss
                             rtp/jit=20,
                             rtp/delay=40 } ; avg latency
             }
          }
      }
   
      21)   When the MGC receives an onhook signal from one of the MGs, it
      brings down the call. In this example, the user at MG2 hangs up
      first.
   
   
   
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      From MG2 to MGC:
   
      MEGACO/1 [125.125.125.111]:55555
      Transaction = 50008 {
         Context = 5000 {
             Notify = A5555 {ObservedEvents =1235 {
                19990729T24020002:al/on(init=false)}
             }
         }
      }
   
      From MGC to MG2:
   
      MEGACO/1 [123.123.123.4]:55555
      Reply = 50008 {
          Context = - {Notify = A5555}
      }
   
      22)   The MGC now sends both MGs a Subtract to take down the call.
      Only the subtracts to MG2 are shown here. Each termination has its
      own set of statistics that it gathers. An MGC may not need to request
      both to be returned. A5555 is a physical termination, and A5556 is an
      RTP termination.
   
      From MGC to MG2:
   
      MEGACO/1 [123.123.123.4]:55555
      Transaction = 50009 {
         Context = 5000 {
            Subtract = A5555 {Audit{Statistics}},
            Subtract = A5556 {Audit{Statistics}}
         }
      }
   
      From MG2 to MGC:
   
      MEGACO/1 [125.125.125.111]:55555
      Reply = 50009 {
         Context = 5000 {
           Subtract = A5555 {
                Statistics {
                   nt/os=45123, ; Octets Sent
                   nt/dur=40 ; in seconds
                   }
             },
             Subtract = A5556 {
                Statistics {
                   rtp/ps=1245, ; packets sent
                   nt/os=62345, ; octets sent
   
   
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                   rtp/pr=780, ; packets received
                   nt/or=45123, ; octets received
                   rtp/pl=10, ;  % packets lost
                   rtp/jit=27,
                   rtp/delay=48 ; average latency
                }
             }
         }
      }
   
      23)   The MGC now sets up both MG1 and MG2 to be ready to detect the
      next off-hook event. See step 1. Note that this could be the default
      state of a termination in the null context, and if this were the
      case, no message need be sent from the MGC to the MG. Once a
      termination returns to the null context, it goes back to the default
      termination values for that termination.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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   APPENDIX II CHANGES FROM RFC XXXX [draft-ietf-megaco-3015corr-02.txt]
   
      Section  Source Description
   
      Abstract PTT    Describes changes between v1 and v2.
   
      1        Edit   Added instructions on indication of versions in
                       ServiceChangeVersion.
   
      2.1      Edit   Added references to H.248.4, H.248.5.
   
      5        PTT    New approach to discrepancy between ITU-T and IETF
                       definition of "SHOULD".
   
      6 para 2 List   Deleted "modem" [parameters] from last sentence.
   
      6.2 para Edit   Replaced "taken out of the call it is in" with
      4                "subtracted from a context".
   
      6.2      Edit   Rewritten to clarify.
      final
      para
   
      6.2.4    List   Added note that use of Modem descriptor is
      table            deprecated.
   
      6.2.5    AVD    Added ability to set signals on ROOT.  Affects first
                       para, Modify.
   
      6.2.5    Edit   Added clarifying phrase "as an entity in itself".
      first
      para
   
      7.1.2    List   Added para spelling out deprecation of Modem
                       descriptor.
   
      7.1.3    AVD    Added Nx64K multiplex type with description.
   
      7.1.7    Edit   Removed "under" in last sentence, so that all cases
      first            of specification can be seen to apply.
      para
   
      7.1.12   AVD    Added ability to specify individual property, event,
                       signal or statistics to be audited.
   
      7.1.12   List   Noted deprecation of Modem descriptor.
   
      7.1.14.3 AVD    Added ability to specify value of "long duration"
   
   
   
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                       threshold within the digit map itself.
   
      7.1.14.4 AVD    Added text requiring digit buffering and spelling
                       out procedures, if EventBufferControl is OFF.
   
      7.1.14.5 AVD    Added text on handling of buffered digits.
      step 2)
   
      7.1.14.5 AVD    Added provision for inclusion of indication of which
      step 2)          timer expired if digit map completion event allows
                       this.
   
      7.1.14.5 AVD    Added text providing alternatives for handling of
      step 5)          excess digits.
   
      7.1.14.7 AVD    Added text on applicability of this clause to
      final            buffered digits.
      bullet
   
      7.1.18   AVD    Added ability to specify topology by stream: mention
                       in para 3, new paras before introduction to figures,
                       new Figure 8.
   
      7.2.1,   List   Deprecation of Modem descriptor noted.
      7.2.2,
      7.2.3,
      7.2.4,
      7.2.5,
      7.2.6
   
      7.2.5,   AVD    Added ability to audit individual property, event,
      7.2.6            signal or statistics.  Added detailed instructions
                       for this.
   
      7.2.8    AVD    Added ability to indicate capability change to be
                       audited: added ServiceChangeInfo to bulleted list of
                       contents of ServiceChange descriptor, added para
                       explaining what it is for.
   
      7.2.8    Edit   Para following new ServiceChangeInfo para: cleanup
                       of wording in second sentence on registration with
                       Failover method.
   
      7.2.8    AVD    Bullet dealing with ServiceChangeProfile on
                       registration: added text on procedures associated
                       with profiles.
   
      7.2.8    AVD    Added 916 and 917 ServiceChangeReasons.
   
   
   
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      7.2.9    AVD    Added text describing the auditing of context
                       properties.
   
      7.3      Edit   Deleted.  Explanation of error descriptors is now in
                       section 7.1.19, and error codes are documented in
                       H.248.8.
   
      8.2.3    AVD    Added text on properties and procedures to limite
                       the number of pending notices sent for a given
                       transaction.
   
      8.3      Edit   Added sentence indicating that messages conforming
      second           to this document specify version 2 of the protocol.
      para
   
      9        Edit   Added mention of H.248.4 and H.248.5 (were
                       transport-related Annexes to H.248).
   
      11       AAP    Second para demoted to Note to resolve objection
                       during ITU-T Last Call process.
   
      11.3     Edit   Modified first sentence to refer specifically to
                       ServiceChange commands constituting registrations.
                       [Hidden issue: reestablishment of contact with
                       Disconnected method does not constitute
                       registration.]  Added second sentence requiring that
                       the registration message always conform to version 1
                       [to ensure interoperability before common working
                       version can be established].
   
      12.1.1   Edit   Slight clarification of "designed to be extended
                       only" description.
   
      13       AVD    New section providing extended description of
                       profile contents and registration.
   
      14 and   Edit   Renumbered as a result of the new Profile section.
      sub-
      sections
   
      14.4     AVD    IANA considerations for profiles added.
   
      A.2      Edit   Added object identifier including version to ASN.1
                       header.
   
      A.2      AVD    Production TopologyRequest: added optional streamId.
   
      A.2      AVD    Production AuditDescriptor: added auditPropertyToken
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
                       term for more specific audit items.
   
      A.2      AVD    New productions IndAuditParameter through
                       IndAudPackagesDescriptor added for more specific
                       audit items.
   
      A.2      AVD    Production MuxType: added nx64k.
   
      A.2      AVD    Production DigitMapValue: added durationTimer term.
   
      A.2      AVD    Production ServiceChangeParm: added
                       serviceChangeInfo term.
   
      A.3      AVD    Production digitMapLetter: added "T" for start
                       timer.
   
      A.3      Edit   Production pathDomainName: added "*" and ".".
   
      B.2      Edit   Production message: version changed to 2 in comment.
   
      B.2      Post-  Production transactionAck: TransactionID
               edit   capitalized.
   
      B.2      PTT    Productions contextID, terminationID, and
                       terminationIDList reordered: grouped with
                       TransactionID to make fundamental productions more
                       visible.
   
      B.2      AVD    Production MuxType: added Nx64kToken.
   
      B.2      AVD    Production digitMapValue: added ["Z" COLON Timer
                       COMMA] alternative.
   
      B.2      AVD    Production digitMapLetter: added "T" (start timer)
                       alternative.
   
      B.2      AVD    Production auditItem: added indAudterminationAudit
                       term.
   
      B.2      AVD    New productions indAudterminationAudit through
                       indAudpackagesDescriptor added for more specific
                       auditing.
   
      B.2      AVD    Production ServiceChangeParm: term auditItem added
                       to indicate nature of capability change.
   
      B.2      AVD    Production topologyTriple: optional eventStream
                       (sic) term added.
   
   
   
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                         Megaco Protocol version 2            April 2003
   
   
      B.2      AVD    New production Nx64kToken.
   
      C.1      Edit   ACodec: reference corrected to Q.765.5
   
      E.2.1    Edit   Editorial correction to informal name of property
                       maxNumberOfContexts.
   
      E.2.1    AVD    Added properties to govern TransactionPending
                       retransmissions.
   
      E.4      Edit   Added extend-only package usage indicator.
   
      E.7.3    Edit   Added "recording" qualifier to warning tone.
      table
   
      E.11.2   Edit   For quality alert event: replaced "property" with
                       "event" in description.
   
      Appendix Edit   Expanded on codec examples.  Added reference to IANA
      I second         registry for RTP payload types.
      para
   
   
   
   
   
   
   
   
   
   
   
   
   INTELLECTUAL PROPERTY RIGHTS
   
      The ITU draws attention to the possibility that the practice or
      implementation of this Recommendation may involve the use of a
      claimed Intellectual Property Right. The ITU takes no position
      concerning the evidence, validity or applicability of claimed
      Intellectual Property Rights, whether asserted by ITU members or
      others outside of the Recommendation development process.
   
      As of the date of approval of this Recommendation, the ITU had
      received notice of intellectual property, protected by patents, which
      may be required to implement this Recommendation. However,
      implementors are cautioned that this may not represent the latest
      information and are therefore strongly urged to consult the TSB
      patent database.
   
   
   
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                              Megaco version 2                 April 2003
   
   
      The IETF has also received notice of intellectual property claims
      relating to Megaco/H.248.1.  Please consult the IETF IPR
      announcements at http://www.ietf.org/ipr.html.
   
   
   Acknowledgments
   
      Megaco/H.248.1 is the result of hard work by many people in both the
      IETF and in ITU-T Study Group 16.  This section records those who
      played a prominent role in ITU-T meetings, on the Megaco list, or
      both.
   
      Megaco/H.248 owes a large initial debt to the MGCP protocol (RFC
      2705), and thus to its authors, Mauricio Arango, Andrew Dugan, Ike
      Elliott, Christian Huitema, and Scott Pickett.  Flemming Andreasen
      does not appear on this list of authors, but was a major contributor
      to the development of both MGCP and Megaco/H.248.1.  RFC 3435 (MGCP)
      has an extensive acknowledgement of many other people who worked on
      media gateway control before Megaco got started.
   
      The authors of the first Megaco RFCs (2885, then 3015) were Fernando
      Cuervo, Nancy Greene, Abdallah Rayhan, Christian Huitema, Brian
      Rosen, and John Segers.  Christian Groves conceived and was editor of
      Annex C.  The people most active on the Megaco list in the period
      leading up to the completion of RFC 2885 were Brian Rosen, Tom
      Taylor, Nancy Greene, Christian Huitema, Matt Holdrege, Chip Sharp,
      John Segers, Michael Thomas, Henry Sinnreich, and Paul Sijben.  The
      people who sacrificed sleep and meals to complete the massive amount
      of work required in the decisive Study Group 16 meeting of February,
      2000, were Michael Brown, Ranga Dendi, Larry Forni, Glen Freundlich,
      Christian Groves, Alf Heidemark, Steve Magnell, Selvam Rengasami,
      Rich Rubin, Klaus Sambor, John Segers, Chip Sharp, Tom Taylor, and
      Stephen Terrill.
   
      The most active people on the Megaco list in the period since the
      February 2000 have been Tom Taylor, Brian Rosen, Christian Groves,
      Madhu Babu Brahmanapally, Troy Cauble, Terry Anderson, Chuong Nguyen,
      and Kevin Boyle, but many other people have been regular
      contributors.  Brian Rosen did tremendous service in putting together
      the Megaco interoperability tests.  On the Study Group 16 side, the
      editorial team for the final document in February, 2002 included
      Christian Groves, Marcello Pantaleo, Terry Anderson, Peter Leis,
      Kevin Boyle, and Tom Taylor.
   
      Tom Taylor as Megaco Chair managed the day to day operation of the
      Megaco list, with Brian Rosen taking an equal share of the burden for
      most of the last three years.  Glen Freundlich as the Study Group 16
      Rapporteur ran the ITU-T meetings and ensured that all of the work at
      hand was completed.  Without Glen's determination the Megaco/H.248
   
   
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                              Megaco version 2                 April 2003
   
   
      standard would have taken at least half a year longer to produce.
      Christian Groves filled in ably as Rapporteur when Glen could no
      longer take part.
   
   
   Authors' Addresses
   
      Terry L Anderson
      Lucent Technologies/INS/Voice Over IP Access Networks
      Rm 2G-219A, 101 Crawfords Corner Rd, Holmdel, NJ 07733-3030
      Phone: +1.732.949.5628
      Email: tla@lucent.com
   
      Christian Groves
      Ericsson AsiaPacificLab Australia
      37/360 Elizabeth St
      Melbourne, Victoria 3000
      Australia
      Email: Christian.Groves@ericsson.com.au
   
      Marcello Pantaleo
      Ericsson Eurolab Deutschland
      Ericsson Allee 1
      52134 Herzogenrath, Germany
      e-mail: Marcello.Pantaleo@eed.ericsson.se
   
      Tom Taylor
      Nortel Networks
      1852 Lorraine Ave,
      Ottawa, Ontario
      Canada K1H 6Z8
      Phone: +1 613 736 0961
      E-mail: taylor@nortelnetworks.com
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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