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Versions: 00 01 02
Internet Engineering Task Force
Internet Draft Rajesh Kumar
Document: draft-rajeshkumar-mmusic-sdp-atm-02.txt Mohamed Mostafa
July 1, 2000 Cisco Systems
Expires: January 1, 2001
Conventions for the use of the Session Description Protocol (SDP)
for ATM Bearer Connections
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-
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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
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Abstract
This document described conventions for using the Session Description
Protocol (SDP) described in RFC2327 for controlling ATM Bearer
Connections, and any associated ATM Adaptation Layer (AAL). The AALs
addressed are Type 1, Type 2 and Type 5. This list of conventions is
meant to be exhaustive. Individual applications can use subsets of
these conventions. Further, these conventions are meant to comply
strictly with the SDP syntax as defined in rfc2327.
1. Introduction
SDP will be used in conjunction with a connection handling /
device control protocol such as Megaco (H.248) [26],
SIP [18] or MGCP [25] to communicate the information
needed to set up ATM bearer connections. These connections include
voice connections, voiceband data connections, clear channel circuit
emulation connections and baseband data connections (such as fax
relay, modem relay, SSCOP, frame relay etc.).
Rajesh Kumar, Mohamed Mostafa [Page 1]
These conventions use standard SDP syntax as defined in rfc2327
to describe the ATM-level and AAL-level connections, addresses and
other parameters. In general, parameters associated with layers
higher than the ATM adaptation layer are included only if they are
tightly coupled to the ATM or AAL layers. Since the syntax conforms to
rfc2327, standard SDP parsers should react in a well-defined and safe
manner on receiving session descriptions based on the SDP conventions
in this document. This
is done by extending the values of fields defined in rfc2327
rather than by defining new fields. This is true for all SDP lines
except the of the media attribute lines, in which case new
attributes are defined. The SDP protocol allows the definition
of new attributes in the media attribute lines which are free-form.
For the remaining lines, the fact that the <networkType> field in
an SDP descriptor
is set to "ATM" should preclude the misinterpretation of extended
parameter values by rfc2327-compliant SDP parsers.
These conventions are meant to address the following ATM applications:
* Applications in which a new SVC is set-up for each service
connection. These SVCs could be AAL1 or AAL5 SVCs or
single-CID AAL2 SVCs.
* Applications in which existing path resources are assigned
to service connections. These resources could be
AAL1 PVCs (or SPVCs), AAL5 PVCs (or SPVCs), AAL2 single-CID
PVCs (or SPVCs), or channels (CIDs) within AAL2 PVCs (or
SPVCs) that multiplex multiple CIDs.
This document is limited to the case when the network type is ATM.
This includes raw RTP encapsulation over AAL5 with no intervening IP
layer [46]. It does not address SDP usage for IP, with or without
ATM as a lower layer.
In some cases, IP connection set-up is independent
of lower layers, which are configured prior to it. For example, AAL5
PVCs that connect IP routers can be used for VoIP calls.
In other cases, VoIP call set-up is closely tied to ATM-level
connection set-up.
This might require a chaining of IP and ATM descriptors, as described in
section 5.7.39.
This document makes no assumptions on who constructs the session
descriptions (media gateway, intermediate ATM/AAL2 switch, media
gateway controller etc.). This will be different in different
applications. Further, it allows the use of one session description
for both directions of a connection (as in SIP applications) or the
use of separate session descriptions for different directions. It
addresses the ATM multicast and anycast capabilities.
This document makes no assumptions about how the SDP description will
be coded. Although the descriptions shown here are encoded as text,
alternate codings are possible:
- Binary encoding such as ASN.1. This is an option (in addition to
text encoding) in the Megaco context.
Rajesh Kumar, Mohamed Mostafa [Page 2]
- Use of extended ISUP parameters (Q.1901) to encode the information in
SDP descriptors, with conversion to/from binary/text-based SDP
encoding when needed.
2. Representation of Certain Fields within SDP description lines
This document uses all the syntactic conventions of standard SDP as
defined in RFC2327.
2.1 Representation of Extension Attributes
The SDP protocol (RFC2327) requires that non-standard attributes
and codec names use an "X-" prefix.
In this internet draft, the "X-" prefix is used consistently for
codec names (Table 1) that have not been registered with IANA.
However, this prefix is not used for the extension SDP attributes
defined in this document. This has been done to enhance legibility.
This document suggests that parsers be flexible in the use of the
"X-" prefix convention. They should accept codec names and
attribute names with or without the "X-" prefix.
2.2 Representation of Parameter Values
Parsers designed to this document should be flexible enough to
accommodate decimal and hexadecimal representations. The former
do not have a prefix, while the latter should use a 0x prefix.
In either case, if the bit field is smaller or larger
than the binary equivalent of the SDP representation, then leading
0 bits should be added or removed as needed. Thus, 3 and
0x3 translate into the following five-bit pattern: 0 0011.
The SDP representations 0x12 and 18 translate into the following
five-bit pattern: 1 0010.
Both single-character and multi-character string values are
enclosed in double quotes (i.e. "). By contrast, single quotes
(i.e. ') are used for emphasizing keywords rather than to
refer to characters or strings.
2.3 Directionality Convention
This section defined the meaning of the terms 'forward' and
'backward' as used in this document. This is specially applicable
to parameters that have a specific direction associated with them.
In this document, 'forward' refers to the direction away from the
Media Gateway, while 'backward' refers to the direction towards the
Media Gateway. This convention must be used in all SDP-based session
descriptions regardless of whether underlying bearer is an SVC, a
dynamically allocated PVC/SPVC or a dynamically allocated CID. This
is regardless of which side originates the service connection. If ATM
SVC or AAL2 Q.2630.1 signaling is used, the directionality convention
is independent of which side originates the SVC or AAL2 connection.
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This provides a simple way of identifying the direction in which a
parameter is applicable, in a manner that is independent of the
underlying ATM or AAL2 bearer. This simplicity comes at a price,
described below.
Note that, the convention used by all ATM/AAL2 signaling
specifications (e.g. Q.2931 Section 1.3.3 and Q.2630.1)
mandates that
forward direction is from the end initiating setup/establishment
via bearer signaling towards the end receiving the
setup/ establishment request. The backward direction is in the
opposite direction. In some cases, the 'forward' and
'backward' directions of the ATM signaling convention might
be the exact opposite of the SDP convention described above,
requiring the media gateway to perform the necessary translation.
An example case in which this is needed is described below.
Consider an SDP description sent by a media gateway
controller to the gateway originating a service-level call.
In the backward SVC call set-up model, this gateway terminates
(rather than originates) an SVC call. The media gateway refers
to the traffic descriptor (and hence the PCR) in the direction
away from this gateway as the forward traffic descriptor and
forward PCR. Clearly, this is at odds with ATM SVC signaling which
refers to this very PCR as the backward PCR. The gateway needs
to be able to perform the required swap of directions. In this
example, the media gateway terminating the service level call
(and hence originating the SVC call) does not need to perform
this swap.
3. Capabilities Provided by SDP conventions
To support these applications, the SDP conventions in this document
provide the following session establishment capabilities:
* Identification by an ATM network element of its own address,
in one of several possible formats. A connection peer can
initiate SVC set-up to this address.
* Identification of the ATM bearer connection that is to be
bound to the narrowband telephony connection. This is either
a VCC in AAL1/AAL5 applications or a channel (identified by
a CID) in AAL2 applications. This is useful in PVC/SPVC
applications.
Note that the difference between the PVCs and SPVCs
is in the way the bearer virtual circuit connection is set
up. From the perspective of this document, the terms PVC and
SPVC are equivalent. This is because the bearer connection is
already set prior to the time when the SDP description is used
to bind it to a narrowband telephony connection.
* In AAL1/AAL5 applications, declaration of a set of payload
types that can be bound to the ATM bearer connection.
RTP payload types that have been registered with IANA are
re-used for AAL1 or AAL5. In the manner of standard SDP,
unregistered payload types are mapped dynamically.
Rajesh Kumar, Mohamed Mostafa [Page 4]
* In AAL2 applications, declaration of a set of profiles that
can be bound to the ATM bearer connection. A mechanism for
dynamically defining custom profiles within the SDP session
description is included. This allows the use of custom
profiles for connections that span multi-network interfaces.
* A means of correlating narrowband telephony connections with
underlying ATM bearer connections. The backbone network
connection identifier or bnc-id specified in ITU Q.BICC
standardization work is used for this purpose. In order to
provide a common SDP base for applications based on
ISUP+/Q.BICC and SIP/SIP+, the neutral term 'eecid' is used
in lieu of 'bnc-id' in the SDP session descriptor.
* A means of specifying the explicit mapping of one codec type
and one packetization period into a service type. Service
types are voice, voiceband data and facsimile. This is useful
in determining the encoding to use when the connection is
upspeeded in response to modem or facsimile tones.
* A means of describing the QoS class, ATM transfer capability /
service category, broadband bearer class, traffic parameters,
CPS parameters and SSCS parameters related the underlying
bearer connection.
4. Format of the ATM Session Description
The sequence of lines in the session descriptions in this document
conforms to rfc2327 [1]. In general, a session description consists of
a session-level part followed by zero or more media-level parts. ATM
session descriptions consist of a session level part followed by one
or two media-level parts. The only two media applicable are the ATM
medium and RTCP control (where applicable).
Session descriptor with one media-level part
v= (protocol version, zero or one line)
o= (origin, zero or one line)
s= (session name, zero or one line)
c= (connection information, one line)
t= (timestamp, zero or one line)
m= (media information and transport address, one line)
b= (bandwidth, zero or one line)
k= (encryption key, zero or one line)
a= (media attribute, zero or more lines)
Session descriptor with two media-level parts
(used in h.323 annex C applications)
Session-level part
v= (protocol version, zero or one line)
o= (origin, zero or one line)
s= (session name, zero or one line)
c= (connection information, one line)
t= (timestamp, zero or one line)
Rajesh Kumar, Mohamed Mostafa [Page 5]
media-level part (audio medium)
m= (media information and transport address, one line)
b= (bandwidth, zero or one line)
k= (encryption key, zero or one line)
a= (media attribute, zero or more lines)
media-level part (control medium)
m= (media information and transport address, one line)
c= (connection information for control only, one line)
In general, the 'v', 'o', 's', and 't' lines are mandatory.
However, in the Megaco [26] context, these lines have been made optional.
The 'o', 's', and 't' lines are omitted in most MGCP applications.
Note that SDP session descriptors for ATM can contain
bandwidth (b=) and encryption key (k=) lines. If used, these lines should
strictly conform to the SDP standard (rfc2327). The bandwidth (b=) line
is redundant in the ATM context since this information can be expressed
with greater precision in the atmFtrfcDesc and atmBtrfcDesc
media attribute lines. The encryption key line (k=) can be used
to indicate an encryption key for the bearer, and a method to
obtain the key. At present, the encryption of ATM and AAL2 bearers
has not been conventionalized, unlike the encryption of RTP payloads.
Nor has the authentication of ATM or AAL2 bearer signaling.
In the ATM and AAL2 contexts, the term 'bearer' can include 'bearer
signaling' as well as 'bearer payloads'.
The order of lines in an ATM session description is exactly in the
rfc2327-conformant order depicted above. However, there is no order
of the media attribute ('a') lines with respect to other 'a' lines.
The SDP protocol version for session descriptions using these
conventions is 0. In conformance with standard SDP, it is strongly
recommended that the 'v' line be included at the beginning of each
SDP session description. In some contexts such as Megaco, the
'v' line is optional and may be omitted unless several session
descriptions are provided in sequence, in which case the
'v' line serves as a delimiter. Depending on the application,
sequences of session descriptions might refer to:
- Different connections or sessions.
- Alternate ways of realizing the same connection or session.
The 'o', 's' and 't' lines are included for strict conformance with
RFC2327. It is possible that these lines might not carry useful
information in some ATM-based narrowband telephony applications.
Therefore, some applications might omit these lines, although
it is recommended that they not do so. For maximum
interoperability, it is preferable that SDP parsers not
reject session descriptions that do not contain these lines.
5. Structure of the Session Description Lines
5.1 The Origin Line
The origin line for an ATM-based narrowband telephony session is
structured as follows:
Rajesh Kumar, Mohamed Mostafa [Page 6]
o=<username> <sessionID> <version> <networkType>
<ATMaddressType> <ATMaddress>
The <username> is set to "-".
The <sessionID> can be set to one of the following:
* an NTP timestamp referring to the moment when the SDP session
descriptor was created.
* a Call ID, connection ID or context ID that uniquely
identifies the session within the scope of a media gateway.
Since calls can comprise multiple connections (sessions),
call IDs are generally not suitable for this purpose.
NTP time stamps can be represented as decimal or hex integers.
The part of the NTP timestamp that refers to an integer number
of seconds is sufficient. Since this is a 32-bit field, the decimal
or hex equivalent of a 32-bit field is adequate if NTP time stamps
are used for this purpose.
On the other hand, call IDs, connection IDs and context IDs can be
represented in decimal or hex format, or as a string of alphanumeric
characters. The MGCP connection ID can be 32 hex digits long.
In general, to cover all cases, the <sessionID>
can comprise of up to 32 digits or 34 alphanumeric characters. The
additional two characters allow the inclusion of a "0x" prefix when
hex numbers are represented alphanumerically.
The <version> refers to the version of the SDP session descriptor
(not that of the SDP protocol). This is can be set to one of the
following:
* 0.
* an NTP timestamp referring to the moment when the SDP session
descriptor was modified. If the SDP session descriptor has not
been modified by an intermediate entity (such as an MGC),
then the <version> timestamp will be the same as the
<sessionId> timestamp, if any.
It is adequate to allow up to 32 decimal or hex digits for
the <version>.
The <networkType> in SDP session descriptions for ATM
applications should be assigned the string value "ATM".
The <ATMaddressType> and <ATMaddress> parameters are identical to
those for the connection information ('c') line. Each of these
parameters can be set to a "-". However, it is not recommended
that these fields be omitted without being set to a "-" since
this is not explicitly allowed by standard SDP (rfc2327). It
is recognized that some parser-builders follow this practice.
Rajesh Kumar, Mohamed Mostafa [Page 7]
5.2 The Session Name Line
In general, the session name line is structured as follows:
s=<sessionName>
For ATM-based narrowband telephony sessions, the <sessionName>
parameter is set to a "-". The resulting
lines is:
s=-
It is not recommended that the <sessionName> be omitted without
being set to a "-" since this is not explicitly allowed by
standard SDP (rfc2327). It is recognized that some parser-builders
follow this practice.
s=-
5.3 The Connection Information Line
The connection information line for ATM-based narrowband telephony
sessions is structured as follows:
c=<networkType> <ATMaddressType> <ATMaddress>
The <networkType> field in the 'c' line should be set to "ATM".
When the SDP description is built by a media gateway, the
<ATMaddress> refers to the ATM address of the media gateway
building the SDP description. When this description is forwarded
to the another gateway, it still contains the original gateway's
ATM address. When the media gateway controller builds part or
all of the SDP description, the local descriptor contains the
ATM address of the local media gateway, while the remote descriptor
contains the ATM address of the remote media gateway. Additionally,
in all contexts, the 'm' line can have an ATM address in the
<virtualConnectionId> subparameter which, if present, is the
remote address if the 'c' line address is local, and vice versa.
The <ATMaddressType> can be NSAP, E164 or GWID (ALIAS).
The <ATMaddress> format depends on the <ATMaddressType>.
NSAP: If the ATMaddressType is NSAP, the ATMaddress is expressed as
a string of 40 hex characters without the "0x" prefix. As an option,
dots can be included after 16-bit fields, with the first dot following
an 8-bit field. The last octet of the NSAP
address is the 'selector' field that is not used for ATM addressing
and is available for non-standard use. The prior six octets of the
NSAP are an IEEE 802 MAC address assigned to the gateway. For
example:
c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
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E164: If the ATMaddressType is E164, the ATMaddress is expressed as
a decimal number with up to 15 digits. For example:
c=ATM E164 9738294382
The use of E.164 numbers in the B-ISDN context is defined in ITU E.191.
There is a disparity between the ATM forum and the ITU
in the use of E.164 numbers for ATM addressing. The ATM forum (e.g. UNI
Signaling 4.0) allows only International Format E.164 numbers, while
the ITU (e.g. Q.2931) allows private numbering plans. Since the goal
of this SDP specification is to interoperate with all bearer signaling
protocols, it allows the use of numbers that do not conform to the
E.164 International Format. However, to maximize overall consistency,
network administrators can restrict the provisioning of numbers to the
E.164 International Format.
GWID (ALIAS): If the ATMaddressType is GWID meaning that the address is a
private Voice Gateway identifier (unique within context of network),
the ATMaddress is expressed as alphanumeric string ("A"-"Z", "a"-"z", "0"-
"9",".","-","_"). For example:
c=ATM GWID officeABCmgx101vism12
Since these SDP conventions can be used for more than gateways, the
string "ALIAS" can be used instead of "GWID" in the 'c' line. Thus,
the example above is equivalent to:
c=ATM ALIAS officeABCmgx101vism12
An example of a GWID (ALIAS)is the CLLI code used for telecom
equipment. For all practical purposes, it should be adequate for the
GWID (ALIAS) to be a variable length string with a maximum size of 32
characters. Since this identifier is private to a network, some
network administrations might restrict it to a smaller size (e.g. 10
characters).
The connection information line is always present in an SDP session
descriptor. However, if there is no address to transmit, this line
can be represented in one of the equivalent ways:
c=ATM - -
This might be used when the address is known a priori. It is not
recommended that <ATMaddressType> or <ATMaddress> be omitted
without being set to a "-" since this is not explicitly allowed
by standard SDP (rfc2327). It is recognized that some parser-builders
follow this practice.
5.4 The Timestamp Line
The timestamp line for an SDP session descriptor is structured as
follows:
t= <startTime> <stopTime>
Rajesh Kumar, Mohamed Mostafa [Page 9]
For ATM-based narrowband telephony sessions, the <startTime>
parameter can be made equal to the NTP timestamp (if any) used for
the <sessionID> in the 'o' line. It can also be set to 0
indicating its irrelevance. If it made equal to the NTP timestamp
in seconds, the fractional part of the NTP timestamp is omitted.
In this case,
it is adequate to allow the hex or decimal equivalent of a 32-bit
field. Per Ref. [49], NTP time stamps need a 32 bit unsigned
representation of seconds, and a 32 bit unsigned representation of
fractional seconds.
The <stopTime> parameter is set to 0 in the ATM-based narrowband
telephony context.
5.5 Media Information Line for AAL1 and AAL5 sessions
See Section 6.0 for the representation, in SDP, of the parameters
in the media information line.
The media information line for AAL1-based narrowband telephony
sessions is structured as follows:
m=audio <virtualConnectionId> AAL1/AVP <payloadType#1>
<payloadType#2>...<payloadType #n>
The media information line for AAL5-based narrowband telephony
sessions is similar, with the exception that the string "AAL5"
replaces the string "AAL1". This is depicted below:
m=audio <virtualConnectionId> AAL5/AVP <payloadType#1>
<payloadType#2>...<payloadType #n>
In most AAL1 and AAL2 applications, the ordering of payload types
implies a preference (preferred payload types before less favored
ones).
Note that it is not possible to make this line identical to the 'm'
line in VoAAL2 due to basic differences between the two
applications.
The <virtualConnectionId> parameter can be in one of two basic
formats: with explicit designation of subparameter types within
the <virtualConnectionId> parameter, or with implicit
inference of subparameter type from subparameter position in
the <virtualConnectionId> parameter.
With explicit designation of subparameter types, the
<virtualConnectionId> parameter can be in one of the following
formats:
* VCCI-<vcci>
* <ATMaddressType>-<ATMaddress>/VCCI-<vcci>
* BCG-<bcg>/VCCI-<vcci>
* PORT-<portId>/VPI-<vpi>/VCI-<vci>
* BCG-<bcg>/VPI-<vpi>/VCI-<vci>
* VPCI-<vpci>/VCI-<vci>
Rajesh Kumar, Mohamed Mostafa [Page 10]
With implicit inference of subparameter type from
subparameter position, the <virtualConnectionId> parameter can
be in one of the following formats:
* <vcci>
* <ATMaddressType>-<ATMaddress>/<vcci>
* <ATMaddress>/<vcci>
* <bcg>/<vcci>
* <portId>/<vpi>/<vci>
* <bcg>/<vpi>/<vci>
* <vpci>/<vci>
In the implicit case, the application context and/or the existence
and positions of hyphens and slashes is used to differentiate
between the various options. Within the SDP
media information line, <vcci>, <portId>, <vpi>, <vci> and <vpci> are
decimal numbers (no prefix) or hexadecimal numbers (0x prefix). The
<ATMaddressType> and <ATMaddress> are identical
to their definitions above for the connection information line with
the difference that this address refers to the remote peer in the
media information line.
A "$" notation implies 'any'. A "$" can be used in lieu the entire
<virtualConnectionId> parameter or some or all of its subparameters.
The constant strings in the <virtualConnectionId> can be retained
in the "$" wildcard or omitted consistent with the 'explicit' and
'implicit' formats described above.
Note that a "$" can be used in lieu of the concatenation
<ATMaddressType>-<ATMaddress> in the following ways:
* The entire concatenation, <ATMaddressType>-<ATMaddress>, is
replaced with a "$".
* <ATMaddress> is replaced with a "$", but <ATMaddressType> is
not.
There are contexts such as SVC-based applications where there
is no need to communicate the <virtualConnectionId> parameter
across the MGC - MG interface. In these contexts,
it is sufficient to use a "$", "$/$" or "$/$/$" for the
<virtualConnectionId> parameter in both directions of
communication.
When the network uses PVCs the VCCI values are pre-provisioned. If
connections are established via SVCs or SPVCs, the VCCI is selected
from the list of available VCCIs. The VCCI can be signaled end-to-
end within the Generic Information Transport (GIT) as part of the
ITU Recommendation Q.2931 Setup message per ITU Recommendation
Q.2941.2. The VCCI glare avoidance scheme defined in [32] and [44]
is not adequate for preventing glare when a pool of existing
PVCs/SPVCs is dynamically assigned to calls. In this
context, a mechanism for glare reduction such as assigning
the nearest available values from different ends of the VCCI range
is needed.
Rajesh Kumar, Mohamed Mostafa [Page 11]
The definition of <vcci> guarantees uniqueness between a pair of ATM
nodes. When the MGC communicates with an ATM MG, it can qualify the
<vcci> with the ATM address of the remote node. Network administrations
have the option of provisioning the <vcci> uniquely in a network,
or in subnets of the network. In this case, the ATM address of the
far end can be omitted.
The <portId> parameter is used to identify the physical trunk port
on a stand-alone gateway or on a multiplexer into which the
gateway is plugged as a tributary module. It can be represented as a
decimal or
hex number of up to 32 digits, or an alphanumeric string of up to 32
characters. In general, to cover all cases, the <portID>
can comprise of up to 32 digits or 34 alphanumeric characters. The
additional two characters allow the inclusion of a "0x" prefix when
hex numbers are represented alphanumerically.
The <vpi> and <vci> have their usual ATM connotation.
In some applications, it is meaningful to use a VPCI, a sixteen
bit field, in SDP descriptors. The VPCI is similar to the VPI, except
for its width and the fact that it retains its value across VP
crossconnects. Normally, the VPCI values are unique within the set
of VPs controlled by an SVC/SPVC signaling channel.
In some applications, it is meaningful to bundle a set of connections
between a pair of ATM nodes into a bearer connection group. The <bcg>
subparameter is an eight bit field that allows the bundling of up
to 255 connections.
Although RTP encapsulation defined in rfc1889 is not used, the
payload type variables are used exactly as defined in rfc1890.
Hence, the protocols used for VoAAL1 and VoAAL5 are identified as
AAL1/AVP and AAL5/AVP in the media information line.
Following the text string "AAL1/AVP" or "AAL5/AVP", there is a
list of payload types. The ordering of these payload types
(preferred codecs before less favored ones) can indicate
preference is some applications. These can be either statically
assigned or dynamically mapped payload types. Encodings that
are not statically mapped to payload types by IANA [31] are to
be dynamically mapped at the time of connection establishment
to payload types in the decimal range 96-127. The SDP 'atmmap'
attribute (similar to 'rtpmap') is used for this purpose.
The following are examples of the use of the media information line
in the descriptions of AAL1 narrowband telephony sessions.
Example 1:
m=audio 27 AAL1/AVP 18 0 96
a=atmmap:96 G727-32
implies that the AAL1 VCCI=27 and that the supported encoding
formats are G.729 (or G.729a), PCM Mu-law and 32 kbps G.727.
Example 2:
m=audio 3/4/50 AAL1/AVP 8 15
Rajesh Kumar, Mohamed Mostafa [Page 12]
implies that the AAL1 virtual circuit used has VPI=4, VCI=50 and is
on trunk port #3. Further, it implies that the encoding formats are
G.711 A-law and G.728.
Example 3:
m=audio $ AAL1/AVP 8 15
implies that any AAL1 VCC may be used (subject to glare rules).
Example 4:
m=audio 2/6/$ AAL1/AVP 8 15
implies that any VCI on VPI= 6 of trunk port #2 may be used.
In some applications, an "-" can be used in lieu of the
<payloadType>. It is also legal to use an "-" instead of
the string "AAL1/AVP". In this case, the coding scheme and
the adaptation schemes are described elsewhere, or defaulted.
Example 5:
m=audio 234 - -
a=aalType:AAL1
Example 6:
m=audio 234 AAL1/AVP -
Examples 5 and 6 both indicate an audio medium, a VCCI of 234, AAL1
adaptation and an unspecified codec.
5.6 Media Information Line for AAL2 sessions
See Section 6.0 for the representation, in SDP, of the parameters
in the media information line.
The media information line for AAL2-based narrowband telephony
sessions is structured as follows:
m=audio <virtualConnectionId> <profileType #1> <profile #1>...
<profile #n1> ... <profileType #M> <profile #1>...
<profile #nM>
In most applications, the ordering of profiles implies
a preference (preferred profiles before less favored ones). If
so, then there can be multiple instances of the same profile
type in the same 'm' line.
Note that it is not possible to make this line identical to the 'm'
line in Voice-over-AAL1 due to basic differences between the two
applications.
The <virtualConnectionId> parameter can be in one of the following
formats:
Rajesh Kumar, Mohamed Mostafa [Page 13]
* <vcci>/<cid>
* <ATMaddressType>-<ATMaddress>/<vcci>/<cid>
* <portId>/<vpi>/<vci>/<cid>
* <bcg>/<vpi>/<vci>/<cid>
* <bcg>/<vcci>/<cid>
* <vpci>/<vci>
The <virtualConnectionId> parameter can be in one of two basic
formats: with explicit designation of subparameter types within
the <virtualConnectionId> parameter, or with implicit
inference of subparameter type from subparameter position in
the <virtualConnectionId> parameter.
With explicit designation of subparameter types, the
<virtualConnectionId> parameter can be in one of the following
formats:
* VCCI-<vcci>/CID-<cid>
* <ATMaddressType>-<ATMaddress>/VCCI-<vcci>/CID-<cid>
* BCG-<bcg>/VCCI-<vcci>/CID-<cid>
* PORT-<portId>/VPI-<vpi>/VCI-<vci>/CID-<cid>
* BCG-<bcg>/VPI-<vpi>/VCI-<vci>/CID-<cid>
* VPCI-<vpci>/VCI-<vci>/CID-<cid>
With implicit inference of subparameter type from
subparameter position, the <virtualConnectionId> parameter can
be in one of the following formats:
* <vcci>/<cid>
* <ATMaddressType>-<ATMaddress>/<vcci>/<cid>
* <ATMaddress>/<vcci>/<cid>
* <bcg>/<vcci>/<cid>
* <portId>/<vpi>/<vci>/<cid>
* <bcg>/<vpi>/<vci>/<cid>
* <vpci>/<vci>/<cid>
In the implicit case, the application context and/or the existence
and positions of hyphens and slashes is used to differentiate
between the various options. Within the SDP
media information line, <vcci>, <portId>, <vpi>, <vci>, <vpci> and
<cid> are decimal numbers (no prefix) or hexadecimal numbers (0x
prefix). The <ATMaddressType> and <ATMaddress> are identical
to their definitions above for the connection information line with
the difference that this address refers to the remote peer in the
media information line.
A "$" notation implies 'any'. A "$" can be used in lieu the entire
<virtualConnectionId> parameter or some or all of its subparameters.
The constant strings in the <virtualConnectionId> can be retained
in the "$" wildcard or omitted consistent with the 'explicit' and
'implicit' formats described above.
Note that a "$" can be used in lieu of the concatenation
<ATMaddressType>-<ATMaddress> in the following ways:
* The entire concatenation, <ATMaddressType>-<ATMaddress>, is
replaced with a "$".
* <ATMaddress> is replaced with a "$", but <ATMaddressType> is
not.
Rajesh Kumar, Mohamed Mostafa [Page 14]
There are contexts such as SVC-based applications where there
is no need to communicate the <virtualConnectionId> parameter
across the media gateway controller - media gateway interface. In these
contexts, it is sufficient to use a "$", "$/$", "$/$/$" or "$/$/$/$"
for the <virtualConnectionId> parameter.
When the network uses PVCs the VCCI values are pre-provisioned. If
connections are established via single-CID SVCs or S/PVCs, the VCCI
is selected from the list of available VCCIs. The VCCI can be
signaled end-to-end within the Generic Information Transport (GIT)
as part of the ITU Recommendation Q.2931 Setup message per ITU
Recommendation Q.2941.2. The VCCI glare avoidance scheme defined in
[32] and [44]
is not adequate for preventing glare when a pool of existing
PVCs/SPVCs is dynamically assigned to calls. In this
context, a mechanism for glare reduction such as assigning
the nearest available values from different ends of the VCCI range
is needed.
The definition of <vcci> guarantees uniqueness between a pair of ATM
nodes. When the MGC communicates with an ATM MG, it can qualify the
<vcci> with the ATM address of the remote node. Network administrations
have the option of provisioning the <vcci> uniquely in a network,
or in subnets of the network. In this case, the ATM address of the
far end can be omitted.
If no intermediate subcell switching or multiplexing is involved,
identical CIDs within the same VCC are used at both MGs.
If intermediate subcell switching or multiplexing is involved,
then the CIDs can be different at the two MGs. However, at
an MG and at the first-hop AAL2 switch it interfaces to, the same
CIDs within the same VCC are used. Since calls can be initiated at
either end, CIDs within the same VCC may be assigned at each end,
giving rise to the possibility of glare. In this context,
a mechanism for glare reduction such as assigning the nearest
available values from different ends of the CID range is needed.
The <portId> parameter is used to identify the physical trunk port
on a stand-alone gateway or on a multiplexer into which the
gateway is plugged as a tributary module. It can be represented as a
decimal or
hex number of up to 32 digits, or an alphanumeric string of up to 32
characters. If represented in hex format, the 32 digits do not include
the "0x" prefix ("x" is not a digit, anyway).
The <vpi> and <vci> have
their usual ATM connotation.
In some applications, it is meaningful to use a VPCI, a sixteen
bit field, in SDP descriptors. The VPCI is similar to the VPI, except
for its width and the fact that it retains its value across VP
crossconnects. Normally, the VPCI values are unique within the set
of VPs controlled by an SVC/SPVC signaling channel.
Rajesh Kumar, Mohamed Mostafa [Page 15]
In some applications, it is meaningful to bundle a set of connections
between a pair of ATM nodes into a bearer connection group. The <bcg>
subparameter is an eight bit field that allows the bundling of up
to 255 connections.
The <profileType> parameter indicates the type of profile. It is
expressed in the format AAL2/<profileClass> where <profileClass>
identifies the source of the definition of the profile.
The <profileClass> can be assigned a string value indicating the
source of the subsequent profile numbers
until the next <profileType> field. The following rules apply to
the contents of the <profileClass> field:
- <profileClass> = "ITU" indicates profiles defined by ITU.
Examples: profiles defined in the I.366.2 specification [13].
- <profileClass> = "ATMF" indicates profiles defined by ATM
forum. Examples: profiles defined in the AF-VTOA-0113
specification [44].
- <profileClass> = "custom" indicates profiles defined by
an organization other than the ITU or ATMF. In multi-vendor
networks where this <profileClass> value is used, care
should be taken to preclude inconsistent definitions.
- <profileClass> = <corporateName>
An equipment vendor or service provider can use its registered,
globally unique corporate name (e.g. Cisco, Telcordia etc.) as a
string value of the <profileClass>. It is suggested that organizations
maintain consistent definitions of the advertised AAL2 profiles
that bear their corporate name.
- The <profileClass> can be based on IEEE Standard 802-1990,
Section 5.1,
which defines the globally unique, IEEE-administered, three-octet
OUIs used in MAC addresses and protocol identifiers. In this case,
the <profileClass> field shall be assigned a string value of
"IEEE:" concatenated with <oui> where <oui> is the hex representation
of a three-octet field identical to the IEEE OUI. As a hex representation,
it can be preceded by a 0x prefix, which can also be omitted. For example,
"IEEE:00000C" refers to Cisco Systems, Inc.
The <profile> parameter is expressed as a decimal number. The value
of <profile> for profiles of the type AAL2/ITU or AAL2/ATMF are in
range 1-255 in accordance with ITU-T I.366.2 Annex P [13] and AF-VTOA-
0113 [44]. For other types of profiles, a range of 1-255 should be
adequate.
For example, the media information line may look like:
m=audio 123/5 AAL2/ITU 1
This media line indicates that the media contains audio. The VCCI
for the AAL2 connection is decimal 123 and the CID is decimal 5. The
AAL2 connection uses ITU profile 1 as defined in I.366.2 [13].
m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
Rajesh Kumar, Mohamed Mostafa [Page 16]
implies that any AAL2 VCC may be used (subject to glare rules). If
this list is preferentially ordered, then AAL2/ITU 8 has the highest
priority.
In some applications, an "-" can be used in lieu of the <profileType>
and <profile #> fields. This is possible when the coding scheme is
described elsewhere e.g. when 'aal2_SSCS_3662' attribute indicates
<faxDemod> = "on" and any other competing options as "off", and the
<aalType> attribute indicates AAL2. An example
of the use of the 'm' line in this case is:
m=audio 123/5 - -
a=aalType:AAL2
a=aal2_SSCS_3662:audio off off on off on off off off - - -
Besides indicating an audio medium, a VCCI of 123 and a CID of 5,
the 'm' line indicates an unspecified profile.
5.7 The Media Attribute Lines
In an SDP line sequence, the media information line 'm' is
followed by one or more media attribute or 'a' lines. Media
attribute lines are per the format below:
a=<attribute>:<value>
or
a=<value>
In general, media attribute lines are optional except when needed to
qualify the media information line. This qualification is necessary
when the "m" line for an AAL1 or AAL5 session specifies a payload
type that needs to be dynamically mapped. The 'atmmap' media
attribute line defined below is used for this purpose.
In attribute lines, subparameters that are meant to be left
unspecified are set to a "-". These are generally inapplicable or, if
applicable, are known by other means such as provisioning. In some
cases, a media attribute line with all parameters set to "-" carries
no information and should be preferably omitted. In other cases,
such as the 'lij' media attribute line, the very presence of the
media attribute line conveys meaning.
There are no restrictions placed by rfc2327 [1] regarding the order
of 'a' lines with respect to other 'a' lines. However, these lines
must not contradict each other or the other SDP lines. Inconsistencies
are not to be ignored
and should be flagged as errors. Repeated lines shall result in the
later lines supplanting earlier ones.
Applications will selectively use the optional media attribute
lines listed below. This is meant to be an exhaustive list for
describing the general attributes of ATM bearer networks. However,
it is recognized that this list might have overlooked some attributes,
which particular applications might need. If these are common
enough for general interoperability between vendors (as opposed
to innovation and proprietary differentiation by particular
vendors), then these should be brought to the attention of the
Rajesh Kumar, Mohamed Mostafa [Page 17]
IETF MMUSIC working group for incorporation into future releases
of this document.
* The attributes defined in RFC2327 which allow indication of
the direction in which a session is active. These are
a=sendonly, a=recvonly, a=sendrecv, a=inactive.
* The 'Ptime' attribute defined in RFC2327. It indicates the
packet period. The 'ptime' media attribute line should not
be used in AAL2 applications, since this information is included
in the profiles listed in the 'm' line. This information can
also be included in the 'vsel', 'dsel' and 'fsel' lines. If
the 'ptime' line is included in AAL2 applications, then it can
be ignored or flagged as an error. The latter is preferred
for robustness and simplicity. The 'ptime' is not applicable
in the AAL1 context, where is should be flagged as an error.
In the AAL5 context,
the 'Ptime' media attribute line, if used, should be consistent
with the 'vsel', 'dsel' and 'fsel' lines, if any. Here,
consistency means the ability to yield a non-empty intersection
with one of these lines.
* The 'atmmap' attribute. In the AAL1 and AAL5 contexts, this is
used to dynamically map payload types into codec strings.
* The 'eecid' attribute. This stands for 'end-to-end connection
identifier'. It provides a means of correlating narrowband
telephony connections with underlying ATM bearer connections.
In the Q.BICC/ISUP+ context, the eecid is synonymous with the
bnc-id (backbone network connection identifier). In the SDP
session description, the more general term 'eecid' is used in
order to provide a common SDP baseline for ATM telephony
applications using Q.BICC/ISUP+ and SIP/SIP+.
* The 'aalType' attribute. This is used to indicate the nature
of the ATM adaptation layer (AAL).
* The 'silenceSupp' attribute, used to indicate the use of
of voice activity detection for silence suppression, and to
optionally parameterize the silence suppression function.
* The 'ecanf' and 'ecanb' attributes, used to indicate the use of
of echo cancellation, and to parameterize the this function.
* The 'gcf' and 'gcb' attributes, used to indicate the use of
of gain control, and to parameterize the this function.
* The 'profiledesc' attribute which can be used to describe
AAL2 profiles. Although any AAL2 profile can be so described,
this attribute is useful for describing, at connection
establishment time, custom profiles that might not be known
to the far end. This attribute applies in the AAL2 context
only.
* The 'vsel' attribute which indicates a prioritized list of
3-tuples for voice service. Each 3-tuple indicates a codec,
an optional packet length and an optional packetization
period. This complements the 'm' line information and should
be consistent with it.
* The 'dsel' attribute which indicates a prioritized list of
3-tuples for voiceband data service. Each 3-tuple indicates a
codec, an optional packet length and an optional packetization
period. This complements the 'm' line information and should
be consistent with it.
Rajesh Kumar, Mohamed Mostafa [Page 18]
* The 'fsel' attribute which indicates a prioritized list of
3-tuples for facsimile service. Each 3-tuple indicates a
codec, an optional packet length and an optional packetization
period. This complements the 'm' line information and should
be consistent with it.
* The 'capability' attribute which indicates the ATM transfer
capability (ITU nomenclature) synonymous with the ATM Service
Category (ATMF nomenclature).
* The 'qosclass' attribute which indicates the QoS class of the
ATM bearer connection.
* The 'bcob' attribute which indicates the broadband connection
oriented bearer class.
* The 'stc' attribute which indicates susceptibility to
clipping.
* The 'upcc' attribute which indicates susceptibility the
user plane connection configuration.
* The 'atmQOSfparms' and 'atmQOSbparms' attributes are
used to describe certain key ATM QoS parameters in the forward
and backward directions respectively.
* The 'aal2QOSfparms' and 'aal2QOSbparms' attributes which
are placeholders for AAL2-level impairments, yet to be defined.
These attributes may be withdrawn if not needed.
* The 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes which are
used to describe ATM traffic descriptor parameters in the
forward and backward directions respectively.
* The 'aal2FtrfcDesc' and 'aal2BtrfcDesc' attributes which
are placeholders for AAL2-level traffic descriptors,
yet to be defined. These attributes may be withdrawn if not
needed.
* The 'abrFparms' and 'abrBparms' attributes which are
used to describe ABR-specific parameters in the
forward and backward directions respectively. These parameters
are per the UNI 4.0 signaling specification [5].
* The 'clkrec' attribute which indicates the clock recovery
method for AAL1 unstructured data transfer (UDT).
* The 'fec' attribute which indicates the use of
forward error correction.
* The 'prtfl' attribute which indicates indicate the fill
level of partially filled cells.
* The 'bearertype' attribute is used to indicate
whether the underlying bearer is an ATM PVC/SPVC, an ATM SVC,
or an AAL2 CID connection within an existing ATM PVC/SPVC.
* When present, the 'structure' attribute is used to indicate
the presence or absence of AAL1 structured data transfer (SDT),
and the size of the SDT blocks.
* When present, the 'sbc' media attribute line denotes the
subchannel count in the case of n x 64 clear channel
communication.
* When present, the 'fcpssdusize' and 'bcpssdusize'
attributes are used to indicate the maximum size of the
CPCS SDU payload in the forward and backward directions.
* When present, the 'aal2CPS' attribute is used to
indicate that an AAL2 CPS sublayer as defined in
ITU I.363.2 [13] is associated with VCC referred to in the
'm' line. Optionally, it can be used to indicate selected
CPS options and parameter values for this VCC.
Rajesh Kumar, Mohamed Mostafa [Page 19]
* When present, the 'aal2_sscs_3661' attribute is used to
indicate the presence of an AAL2 SSCS sublayer as defined
in ITU I.366.1 [12]. Optionally, it can be used to indicate
selected options and parameter values for this SSCS.
* When present, the 'aal2_SSCS_3662' attribute is used to
indicate the presence of an AAL2 SSCS sublayer as defined
in ITU I.366.2. Optionally, it can be used to indicate
selected options and parameter values for this SSCS.
* When present, the 'aal2_sscs_3652' attribute is used to
indicate the use, in conjunction with AAL2, of a
service-specific coordination function, as defined in
ITU I.365.2 [40], for Connection Oriented Network Service
(SSCF-CONS).
* When present, the 'aal2_sscs_3653' attribute is
used to indicate the use, in conjunction with AAL2,
of a service-specific coordination function, as defined
in ITU I.365.3 [41], for Connection Oriented Transport Service
(SSCF-COTS).
* When present, the 'AAL5app' attribute is used to
indicate the presence of an application that uses AAL5,
and to point to the controlling standard for the
application layer.
* When present, the 'lij' attribute is used to indicate the
presence of a connection that uses the Leaf-initiated-join
capability described in UNI 4.0 [5], and to optionally
describe parameters associated with this capability.
* When present, the 'anycast' attribute line is used to
indicate the applicability of the anycast function described
in UNI 4.0 [5], and to optionally qualify it with certain
parameters.
* When present, the 'wtp' media attribute line is used to specify
the circuit used to deliver a tapped stream.
* The 'fmtp' attribute line defined in the SDP standard can be
used to describe higher-layer parameters. These that pertain
to layers higher than the ATM adaptation layer and that are
not closely coupled with the ATM or ATM adaptation layers.
Examples are the B-HLI and B-LLI IEs specified in ITU Q.2931 [15],
and the user-to-user information element described in
ITU Q.2957 [48].
* The 'chain' attribute line is used to chain consecutive SDP
descriptions.
5.7.1 The 'atmmap' attribute
The 'atmmap' attribute is defined on the basis of the 'rtpmap'
attribute used in RFC2327.
a=atmmap:<payloadType> <encodingName>
The 'atmmap' attribute is used to dynamically map encoding names
into payload types. This is necessary for those encoding names which
have not been assigned a static payload type through IANA. Payload
types and encoding techniques that have been registered with IANA
for RTP are retained for narrowband telephony based on AAL1 or
AAL5.
Rajesh Kumar, Mohamed Mostafa [Page 20]
The range of statically defined payload types is in the range
0-95. All static assignments of payload types to codecs are
listed in [31]. The range of payload types defined dynamically
via the 'atmmap' attribute is 96-127.
The encoding names in Table 1 are case-insensitive.
Table 1: Encoding Names and Payload Types
|---------------------|--------------|---------------------------|
| Encoding Technique | Encoding Name| Payload type |
|---------------------|--------------|---------------------------|
| PCM - Mu law | "PCMU" | 0 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| 32 kbps ADPCM | "G726-32" | 2 (Statically Mapped) |
|---------------------|--------------|---------------------------|
|Dual rate 5.3/6.3kbps| "G723" | 4 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| PCM- A law | "PCMA" | 8 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| 7 KHz audio coding | "G722" | 9 (Statically Mapped) |
| within 64 kbps | | |
|---------------------|--------------|---------------------------|
| LD-CELP | "G728" | 15 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| CS-ACELP | "G729" | 18 (Statically Mapped) |
|(normal/low-complexity) | |
|---------------------|--------------|---------------------------|
| Low-complexity | "X-G729a" | None, map dynamically |
| CS-ACELP | | |
|---------------------|--------------|---------------------------|
|Normal | "X-G729b" | None, map dynamically |
|CS-ACELP w/ ITU | | |
|defined silence | | |
|suppression | | |
|---------------------|--------------|---------------------------|
|Low-complexity | "X-G729ab" | None, map dynamically |
|CS-ACELP w/ ITU | | |
|defined silence | | |
|suppression | | |
|---------------------|--------------|---------------------------|
| 16 kbps ADPCM | "X-G726-16" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 24 kbps ADPCM | "X-G726-24" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 40 kbps ADPCM | "X-G726-40" | None, map dynamically |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231-H" | None, map dynamically |
| kbps - high rate | | |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231-L" | None, map dynamically |
| kbps - low rate | | |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231a-H" | None, map dynamically |
| kbps - high rate w/ | | |
| ITU-defined silence | | |
| suppression | | |
|---------------------|--------------|---------------------------|
Rajesh Kumar, Mohamed Mostafa [Page 21]
------------------------------------------------------------------
| Dual rate 5.3/6.3 |"X-G7231a-L" | None, map dynamically |
| kbps - high rate w/ | | |
| ITU-defined silence | | |
| suppression | | |
|---------------------|--------------|---------------------------|
| 16 kbps EADPCM | "X-G727-16" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 24 kbps EADPCM | "X-G727-24" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 32 kbps EADPCM | "X-G727-32" | None, map dynamically |
|---------------------|--------------|---------------------------|
|n x 64 kbps Clear | "X-CCD" | None, map dynamically |
|Channel without CAS | | |
|per af-vtoa-78 [7] | | |
|---------------------|--------------|---------------------------|
|n x 64 kbps Clear | "X-CCD-CAS" | None, map dynamically |
|Channel with CAS | | |
|per af-vtoa-78 [7] | | |
|---------------------|--------------|---------------------------|
|GSM Full Rate | "GSM" | 3 (Statically Mapped) |
|---------------------|--------------|---------------------------|
|GSM Half Rate | "X-GSM-HR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|GSM-Enhanced Full Rate "X-GSM-EFR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|GSM-Enhanced Half Rate "X-GSM-EHR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Group 3 fax demod. "X-FXDMOD-3" | None, map dynamically |
|---------------------|--------------|---------------------------|
5.7.2 The 'eecid' attribute
The 'eecid' attribute is synonymous with the 4-byte'bnc-id'
parameter used by T1SI, the ATM forum and the ITU (Q.1901)
standardization effort. The term 'eecid' stands for 'end-to-end
connection identifier', while 'bnc-id' stands for 'backbone network
connection identifier'. The name "backbone" is slightly misleading
since it refers to the entire ATM network including the ATM edge and
ATM core networks. In Q.1901 terminology, an ATM "backbone"
connects TDM or analog edges.
Rajesh Kumar, Mohamed Mostafa [Page 22]
While the term 'bnc-id' might be used in the bearer signaling plane
and in an ISUP (Q.1901) call control plane, SDP session descriptors
use the neutral term 'eecid'. This provides a common SDP baseline
for applications that use ISUP and applications that use
SIP/SIP+.
In the forward SVC establishment model, the call-originating gateway
initiates SVC establishment and transmits an eecid to the call-
terminating gateway via SDP.
In backward SVC establishment model, the call-originating gateway
does not initiate SVC establishment. However, it transmits an
eecid to the call-terminating gateway via SDP. The call-terminating
gateway initiates SVC establishment.
The value of the eecid attribute values needs to be unique within
the gateway initiating the SVC set-up but not across multiple
gateways. Hence, the SVC-initiating gateway has complete control
over using and releasing values of this parameter. The eecid
attribute is used to correlate, one-to-one, received SVC SETUP
requests with service connection requests from the media gateway
controller. In the forward call model, the call-terminating gateway
uses the ATM address of the call-originating gateway in the 'c' line
of the session description to qualify the eecid. This is because
multiple call-originating gateways can sending identical eecids.
Within an SDP session description, the eecid attribute is used as
follows:
a=eecid:<eecid>
where <eecid> consists of up to 8 hex digits (equivalent to 4
octets).
This SDP document does not specify how the eecid (synonymous
with bnc-id) is to be communicated through bearer signaling
(Q.931, UNI, PNNI, AINI, IISP, proprietary signaling equivalent,
Q.2630.1). This is a task of these bearer signaling protocols.
However, the following informative statements are made to
convey a sense of the interoperability that is a goal of
current standardization efforts:
- ITU Q.2941.3 and the ATMF each recommend the use of the
GIT IE for carrying the eecid (synonymous with bnc-id)
in the set-up message of ATM signaling protocols (Q.2931,
UNI 4.0, PNNI, AINI, IISP).
The coding for carrying the eecid (bnc-id) in the GIT IE
is defined in ITU Q.2941.3 and accepted by the ATM forum.
- Another alternate method is to use the called party
subaddress IE in the backward SVC call establishment model,
and the calling party subaddress IE in the forward SVC call
establishment model. This might be construed to be a protocol
violation and is not the recommended means of carrying
the eecid (bnc-id). The GIT IE is the preferred method of
transporting the eecid (bnc-id) in ATM signaling messages.
Rajesh Kumar, Mohamed Mostafa [Page 23]
- The establish request (ERQ) message of the Q.2630.1 [37]
signaling protocol can use the SUGR (Served User Generated
Reference) IE to transport the eecid (bnc-id).
In the backward path set-up model, the call-originating gateway can
release and re-use an eecid when it receives Q.2931 set-up or
Q.2630.1 establish request from the call-terminating end.
In the forward path set-up model, the call-originating gateway can
release and re-use an eecid when it receives a Q.2931 [15] connect or
Q.2630.1 [37] establish confirm from the call-terminating end. This
message need not carry the eecid. The Q.2931 call reference or the
Q.2630.1 Destination Signaling Association Identifier (DSAID) points
to the eecid.
However, in both cases (backward and forward models),
it is recommended that this eecid be retained until the connection
terminates since it can serve as a handle for applications such
as lawful wiretaps (CALEA).
5.7.3 The 'aalType' attribute
When present, the 'aalType' attribute is used to indicate
the ATM adaptation layer. If this information is redundant
with the 'm' line, it can be omitted. The format of the
'aalType' media attribute line is as follows:
a=aalType: <aalType>
Here, <aalType> can take on the following string values:
"AAL1", "AAL1_SDT", "AAL1_UDT", "AAL2", "AAL3/4", "AAL5"
and "User defined AAL".
Note that this document addresses AAL1, AAL2 and AAL5 only.
Currently, there are no known narrowband telephony applications
or standards that use AAL3/4.
5.7.4 The 'silenceSupp' attribute
When present, the 'silenceSupp' attribute is used to indicate
the use or non-use of silence suppression.
The format of the 'silenceSupp' media attribute line is
as follows:
a=silenceSupp: <silenceSuppEnable> <silenceTimer> <suppPref> <sidUse>
<fxnslevel>
If any of the parameters in the silenceSupp media attribute line
is not specified, is inapplicable or is implied, then it is set to
"-".
The <silenceSuppEnable> can take on values of "on" or "off". If it
is "on", then silence suppression is enabled.
The <silenceTimer> is a 16-bit field which can be represented in
decimal or hex. Each increment (tick) of this timer represents
a millisecond. The maximum value of this timer is between 1 and 3
minutes. This timer represents the time-lag before silence
suppression kicks in. Even though this can, theoretically, be
as low as 1 ms, most DSP algorithms take more than that to
Rajesh Kumar, Mohamed Mostafa [Page 24]
detect silence. Setting <silenceTimer> to a large value (say
1 minute> is equivalent to disabling silence suppression
within a call. However, idle channel suppression between calls
on the basis of silence suppression is still operative in
non-switched, trunking applications if <silenceSuppEnable> = "on"
and <silenceTimer> is a large value.
The <suppPref> specifies the preferred silence suppression
method that is preferred or already selected. It can
take on the string values of "standard" and "custom". If
its value is "standard", then a standard method (e.g. ITU-defined)
is preferred to custom methods if such a standard
is defined. Otherwise, a custom method may be used. If
<suppPref> is set to "custom", then a custom method, if
available, is preferred to the standard method.
The <sidUse> indicates whether SIDs (Silence Insertion
Descriptors) are to be used, and whether they use fixed comfort
noise or sampled background noise. It can take on the
string values of "No SID", "Fixed Noise", "Sampled Noise".
If the value of <sidUse> is "Fixed Noise", then <fxnslevel>
provides its level. It can take on integer values in the range
0-127, as follows:
<fxnslevel> value Meaning
0-29 Reserved
30 -30 dBm0
31 -31 dBm0
. . . . . .
77 -77 dBm0
78 -78 dBm0
79-126 reserved
127 Idle Code (no noise)
A hex representation, preceded by a 0x prefix, of <fxnslevel>
is allowed.
5.7.5 The 'ecanf' and 'ecanb' attributes
When present, the 'ecanf' and 'ecanb' attributes are used to indicate
the use or non-use of echo cancellation in the forward
and backward directions respectively. See Section
2.3 for a definition of the terms 'forward' and 'backward'.
The format of the 'ecanf' and 'ecanb' media attribute lines is
as follows:
a=ecanf: <ecanEnable> <ecanType>
a=ecanb: <ecanEnable> <ecanType>
If any of the parameters in the ecanf and ecanb media attribute lines
is not specified, is inapplicable or is implied, then it is set to
"-".
Rajesh Kumar, Mohamed Mostafa [Page 25]
If the 'ecanf' or 'ecanb'
media attribute lines is not present, then means other than
the SDP descriptor must be used to determine the applicability
and nature of echo cancellation in that direction. Examples
of such means are MIB provisioning, the local connection options
structure in MGCP etc.
The <ecanEnable> parameter can take on values of "on" or "off". If it
is "on", then echo cancellation is enabled. If it is "off",
then echo cancellation is disabled.
The <ecanType> parameter can take on the string values "G165" and "G168"
respectively.
When SDP is used with some media gateway control protocols such as MGCP
and Megaco [26], there exist means outside SDP descriptions to specify
the echo cancellation properties of a connection. Nevertheless, this
media attribute line is included for completeness. As a result, the
SDP can be used for describing echo cancellation in applications
where alternate means for this are unavailable.
5.7.6 The 'gcf' and 'gcb' attributes
When present, the 'gcf' and 'gcb' attributes are used to indicate
the use or non-use of gain control in the forward
and backward directions respectively. See Section
2.3 for a definition of the terms 'forward' and 'backward'.
The format of the 'gcf' and 'gcb' media attribute lines is
as follows:
a=gcf: <gcEnable> <gcLvl>
a=gcb: <gcEnable> <gcLvl>
If any of the parameters in the gcf and gcb media attribute lines
is not specified, is inapplicable or is implied, then it is set to
"-".
If the 'gcf' or 'gcb'
media attribute line is not present, then means other than
the SDP descriptor must be used to determine the applicability
and nature of gain control in that direction. Examples of such
means are MIB provisioning, the local connection options
structure in MGCP etc.
The <gcEnable> parameter can take on values of "on" or "off". If it
is "on", then gain control is enabled. If it is "off", then
gain control is disabled.
The <gcLvl> parameter is represented as the decimal or hex
equivalent of a 16-bit binary field. A value of 0xFFFF implies
automatic gain control. Otherwise, this number indicates the
number of decibels of inserted loss. The upper bound, 65,535 dB
(0xFFFE) of inserted loss, is an absurdly large number and is a
carryover from Megaco [26]. In practical applications, the inserted loss
is much lower.
Rajesh Kumar, Mohamed Mostafa [Page 26]
When SDP is used with some media gateway control protocols such as MGCP
and Megaco [26], there exist means outside SDP descriptions to specify
the gain control properties of a connection. Nevertheless, this
media attribute line is included for completeness. As a result, the
SDP can be used for describing gain control in applications
where alternate means for this are unavailable.
5.7.7 The 'profiledesc' attribute
There is one 'profiledesc' media attribute line for each AAL2
profile that is intended to be described. The 'profiledesc' media
attribute line is structured as follows:
a=profiledesc: <profileType> <profile> <uuiCodeRange#1>
<encodingName#1> <packetLength#1> <packetTime#1>
<uuiCodeRange#2> <encodingName#2> <packetLength#2>
<packetTime#2>... <uuiCodeRange#N> <encodingName#N>
<packetLength#N> <packetTime#N>
Here, <profileType> and <profile> are identical to their
definition, above, for the 'm' line.
The profile elements (rows in the profile tables of ITU I.366.2 or
AF-VTOA-0113) are represented as four-tuples following the <profile>
parameter in the 'profiledesc' media attribute line. If a member of
one of these four-tuples is not specified or is implied, then it is
set to "-".
The <uuiCodeRange> parameter is represented by D1-D2, where D1 and
D2 are decimal integers in the range 0 through 15.
The <encodingName> parameter can take one of the values in column 2
of Table 1. Additionally, it can take on the following descriptor
strings: "PCMG", "SIDG" and "SID729". These stand for generic PCM,
generic SID and G.729 SID respectively.
The <packetLength> is a decimal integer representation of the AAL2
packet length in octets.
The <packetTime> is a decimal integer representation of the AAL2
packetization interval in ms.
For instance, the 'profiledesc' media attribute line below defines
the AAL2/custom 100 profile. This profile is reproduced in the table
below. For a description of the parameters in this profile such as
M and the sequence number interval, see ITU I.366.2.
a=profiledesc:AAL2/custom 100 0-7 PCMG 40 5 0-7 SIDG 1 5 8-15
G726-32 40 10 8-15 SIDG 1 5
If the <packetTime> parameter is to be omitted or implied, then the
same profile can be represented as follows:
a=profiledesc:AAL2/custom 100 0-7 PCMG 40 - 0-7 SIDG 1 - 8-15
G726-32 40 - 8-15 SIDG 1 -
Rajesh Kumar, Mohamed Mostafa [Page 27]
If a gateway has a provisioned or hard coded definition of a
profile, then any definition provided via the 'profiledesc' line
overrides it. The exception to this rule is with regard to standard
profiles such as ITU-defined profiles and ATMF-defined profiles. In
general, these should not be defined via a 'profiledesc' media
attribute line. If they are, then the definition needs to be
consistent with the standard definition else the SDP session
descriptor should be rejected with an appropriate error code.
|---------------------------------------------------------------|
| UUI | Packet |Encoding | | |Packet|Seq.No. |
| Code | Length |per ITU |Description of | M |Time |Interval|
|point |(octets)|I.366.2 | Algorithm | |(ms) |(ms) |
|Range | | 2/99 | | | | |
| | | version | | | | |
|---------------------------------------------------------------|
| 0-7 | 40 | Figure | PCM, G.711-64,| 1 | 5 | 5 |
| | | B-1 | generic | | | |
|------|--------|---------|---------------|-----|------|--------|
| 0-7 | 1 | Figure | Generic SID | 1 | 5 | 5 |
| | | I-1 | | | | |
|------|--------|---------|---------------|-----|------|--------|
| 8-15 | 40 | Figure | ADPCM, | 2 | 10 | 5 |
| | | E-2 | G.726-32 | | | |
|------|--------|---------|---------------|-----|------|--------|
| 8-15 | 1 | Figure | Generic SID | 1 | 5 | 5 |
| | | I-1 | | | | |
|------|--------|---------|---------------|-----|------|--------|
5.7.8 The 'vsel' attribute
The 'vsel' attribute which indicates a prioritized list of
one or more
3-tuples for voice service. Each 3-tuple indicates a codec,
an optional packet length and an optional packetization
period. This complements the 'm' line information and should
be consistent with it.
The 'vsel' line is structured as follows:
a=vsel:<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
where the <encodingName> parameter can take one of the values in
column 2 of Table 1. The <packetLength> is a decimal integer
representation of the packet length in octets. The <packetTime> is a
decimal integer representation of the
packetization interval in ms. The parameters
<packetLength>and <packetTime> can be set to "-" when not needed.
Also, the entire 'vsel' media attribute line can be omitted when not
needed.
Rajesh Kumar, Mohamed Mostafa [Page 28]
For example,
a=vsel:G729 10 10 G726-32 40 10
indicates first preference of G.729 or G.729a (both are
interoperable) as the voice encoding scheme. A packet length of 10
octets and a packetization interval of 10 ms are associated with
this codec. G726-32 is the second preference stated in this line,
with an associated packet length of 40 octets and a packetization
interval of 10 ms. If the packet length and packetization
interval are intended to be omitted, then this media attribute line
becomes
a=vsel:G729 - - G726-32 - -
The media attribute line
a=vsel:G726-32 40 10
indicates preference for or selection of 32 kbps ADPCM with a packet
length of 40 octets and a packetization interval of 10 ms.
This media attribute line can be used in the AAL1, AAL2 and
AAL5 contexts. In the AAL1 context, it has the very limited
utility of indicating whether the codec type is PCMU or PCMA.
The <packetLength> and <packetTime> are not meaningful in this
case, and should be set to "-". Its greatest utility in AAL2,
where it determines the use of some or all of the rows in
a given profile table. If multiple 3-tuples are present, they
can indicate a hierarchical assignment of some rows in that
profile to voice service e.g. row A preferred to row B etc.
If multiple profiles are present on the 'm' line, the profile
qualified by this attribute is the first (i.e. highest priority)
profile.
5.7.9 The 'dsel' attribute
The 'dsel' attribute which indicates a prioritized list of
one or more 3-tuples for voiceband data service. The <fxIncl>
flag indicates whether this definition of voiceband data
includes fax ("on" value) or not ("off" value). If <fxIncl> is
"on", then the 'dsel' line must be consistent with any 'fsel' line
in the session description. In this case, an
error event is generated in the case of inconsistency.
Each 3-tuple indicates a codec,
an optional packet length and an optional packetization
period. This complements the 'm' line information and should
be consistent with it.
The 'dsel' line is structured as follows:
a=dsel:<fxIncl> <encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
where the <encodingName> parameter can take one of the values in
column 2 of Table 1. The <packetLength> and <packetTime>
parameters are per their definition, above, for the 'vsel'
Rajesh Kumar, Mohamed Mostafa [Page 29]
media attribute line. The parameters
<packetLength>and <packetTime>) can be set to "-" when not needed.
The <fxIncl> flag is presumed to be "off" if it is set to "-".
Also, the entire 'dsel' media attribute line can be omitted when not
needed.
For example,
a=dsel:- G726-32 20 5 PCMU 40 5
indicates that this line does not address facsimile, and that the
first preference for the voiceband data codes is 32 kbps ADPCM,
while the second preference is PCMU. The packet length
and the packetization interval associated with G726-32 are 20 octets and
5 ms respectively. For PCMU, they are 40 octets and 5 ms respectively.
This media attribute line can be used in the AAL1, AAL2 and
AAL5 contexts. In the AAL1 context, it has the very limited
utility of indicating whether the codec type is PCMU or PCMA.
The <packetLength> and <packetTime> are not meaningful in this
case, and should be set to "-". Its greatest utility in AAL2,
where it determines the use of some or all of the rows in
a given profile table. If multiple 3-tuples are present, they
can indicate a hierarchical assignment of some rows in that
profile to voiceband data service e.g. row A preferred to row B etc.
If multiple profiles are present on the 'm' line, the profile
qualified by this attribute is the first (i.e. highest priority)
profile.
5.7.10 The 'fsel' attribute
The 'fsel' attribute which indicates a prioritized list of
one or more 3-tuples for facsimile service. If an 'fsel' line
is present, any 'dsel' line with <fxIncl> set to "on" in the session
description must be checked for consistency with it. In this case,
an error event is generated in the case of inconsistency.
Each 3-tuple indicates a codec,
an optional packet length and an optional packetization
period. This complements the 'm' line information and should
be consistent with it.
The 'fsel' line is structured as follows:
a=dsel:<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
where the <encodingName> parameter can take one of the values in
column 2 of Table 1. The <packetLength> and <packetTime>
parameters are per their definition, above, for the 'vsel'
media attribute line. The parameters
<packetLength>and <packetTime> can be set to "-" when not needed.
Also, the entire 'fsel' media attribute line can be omitted when not
needed.
For example,
Rajesh Kumar, Mohamed Mostafa [Page 30]
a=fsel:FXDMOD-3 - -
indicates demodulation and remodulation of ITU-T group 3 fax at the
gateway.
a=fsel:PCMU 40 5 G726-32 20 5
indicates a first and second preference of Mu-law PCM and 32 kbps
ADPCM as the facsimile encoding scheme. The packet length
and the packetization interval associated with G726-32 are 20 octets and
5 ms respectively. For PCMU, they are 40 octets and 5 ms respectively.
This media attribute line can be used in the AAL1, AAL2 and
AAL5 contexts. In the AAL1 context, it has the very limited
utility of indicating whether the codec type is PCMU or PCMA.
The <packetLength> and <packetTime> are not meaningful in this
case, and should be set to "-". Its greatest utility in AAL2,
where it determines the use of some or all of the rows in
a given profile table. If multiple 3-tuples are present, they
can indicate a hierarchical assignment of some rows in that
profile to facsimile service e.g. row A preferred to row B etc.
If multiple profiles are present on the 'm' line, the profile
qualified by this attribute is the first (i.e. highest priority)
profile.
5.7.11 The 'capability' attribute
When present, the 'capability' attribute indicates the ATM Transfer
Capability described in ITU I.371 [28], equivalent to the ATM Service
Category described in the UNI 4.1 Traffic Management specification [6].
The 'capability' media attribute line is structured in one of
the following ways:
a=capability: <asc> <configuration>
a=capability: <atc> <configuration>
Possible values of the <asc> are enumerated
below:
"CBR", "nrt-VBR", "rt-VBR", "UBR", "ABR", "GFR"
Possible values of the <atc> are enumerated
below:
"DBR","SBR","ABT/IT","ABT/DT","ABR"
Some applications might use non-standard <atc> and <asc> values
not listed above. Equipment designers will need to agree on
the meaning and implications of non-standard transfer
capabilities / service capabilities. An example of a
a non-standard <asc> value is "UBR+", which is UBR with
minimum cell rate (MCR).
Rajesh Kumar, Mohamed Mostafa [Page 31]
The <configuration> field essentially serves as a subscript
to the <asc> and <atc> fields. In general, it can
take on any integer value, or the "-" value indicating that
it does not apply or that the underlying data is to be known
by other means, such as provisioning.
The following combinations are recognized in the ATMF and
ITU specifications:
<atc> <configuration> Meaning
nrt-VBR 1 nrt-VBR.1
nrt-VBR 2 nrt-VBR.2
nrt-VBR 3 nrt-VBR.3
rt-VBR 1 rt-VBR.1
rt-VBR 2 rt-VBR.2
rt-VBR 3 rt-VBR.3
UBR 1 UBR.1
UBR 2 UBR.2
GFR 1 GFR.1
GFR 2 GRR.2
<atc> <configuration> Meaning
SBR 1 SBR1
SBR 2 SBR2
SBR 3 SBR3
It is beyond the scope of this specification to examine the
equivalence of some of the ATMF and ITU definitions. These
need to be recognized from the ATMF and ITU
source specifications and exploited, as much as possible,
to simplify ATM node design.
These string values in the 'capability' attribute are case-
insensitive. When the bearer connection is a single AAL2 CID
connection within a multiplexed AAL2 VC, the 'capability'
attribute does not apply.
5.7.12 The 'qosclass' attribute
When present, the 'qosclass' attribute indicates the QoS class
specified in ITU I.2965.1 [34].
The 'qosclass' media attribute line is structured as follows:
a=qosclass: <qosclass>
Here, <qosclass> is an integer in the range 0 - 5.
<qosclass> Meaning
0 Default QoS
1 Stringent
2 Tolerant
3 Bi-level
4 Unbounded
5 Stringent bi-level
Rajesh Kumar, Mohamed Mostafa [Page 32]
5.7.13 The 'bcob' attribute
When present, the 'bcob' attribute represents the broadband
connection oriented bearer class defined in ITU Q.2961.2 [33].
The 'bcob' media attribute line is structured as
follows:
a=bcob: <bcob>
Here, <bcob> is the decimal or hex representation of a 5-bit
field. Currently, all values are unused and
reserved with the following exceptions:
<bcob> Meaning
1 BCOB-A
3 BCOB-C
16 BCOB-X
24 BCOB-VP (transparent VP service)
5.7.14 The 'stc' attribute
When present, the 'stc' attribute represents susceptibility
to clipping. The 'stc' media attribute line is structured as
follows:
a=stc: <stc>
Here, <stc> is the decimal equivalent of a 2-bit field.
Currently, all values are unused and reserved with the
following exceptions:
<stc> value Binary Equivalent Meaning
0 00 Not susceptible to clipping
1 01 Susceptible to clipping
5.7.15 The 'upcc' attribute
When present, the 'upcc' attribute represents the user plane
connection configuration. The 'upcc' media attribute line is
structured as follows:
a=upcc: <upcc>
Here, <upcc> is the decimal equivalent of a 2-bit field.
Currently, all values are unused and reserved with the
following exceptions:
<upcc> value Binary Equivalent Meaning
0 00 Point to point
1 01 Point to multipoint
5.7.16 The 'atmQOSfparms' and 'atmQOSbparms' attributes
When present, the 'atmQOSfparms' and 'atmQOSbparms'
attributes are used to describe certain key ATM QoS parameters
in the forward and backward directions respectively. See Section
Rajesh Kumar, Mohamed Mostafa [Page 33]
2.3 for a definition of the terms 'forward' and 'backward'.
The 'atmQOSfparms' and 'atmQOSbparms' media attribute lines
are structured as follows:
a=atmQOSfparms: <cdvType><acdv><ccdv><actd><cctd><aclr>
a=atmQOSbparms: <cdvType><acdv><ccdv><actd><cctd><aclr>
The <cdvType> parameter can take on the string values of
"pp" and "2p". These refer to the peak-to-peak and two-point
CDV as defined in UNI 4.0 [5] and ITU Q.2965.2 [35] respectively.
The CDV parameters, <acdv> and <ccdv>, refer to the acceptable
and cumulative CDVs respectively. These are expressed in units
of microseconds and represented as the decimal or hex equivalent
of 24-bit fields. These use the cell loss ratio, <aclr>, as the
"alpha" quantiles defined in the ATMF TM 4.1 specification [6]
and in ITU I.356 [47].
The CTD parameters, <actd> and <cctd>, refer to the acceptable and
cumulative CTDs respectively in milliseconds.
These are represented as the decimal or hex
equivalent of 16-bit fields.
These parameters are equivalent to the maximum end-to-end
transit delay defined in ATMF TM 4.1
specification [6] and Q.2965.2 [35].
The <aclr> parameter refers to forward and backward acceptable
cell loss ratios. This is the ratio between the number of cells
lost and the number of cells transmitted. It is
expressed as the decimal or hex equivalent of an 8-bit field. This field
expresses an order of magnitude n, where n is an integer in the range
1-15. The Cell Loss Ratio takes on the value 10 raised to the power
of minus n.
If any of these parameters is not specified, is inapplicable or is
implied, then it is set to "-".
An example use of these attributes for an rt-VBR,
single-CID AAL2 voice VC is:
a=atmQOSfparms:pp 8125 3455 32000 - 11
a=atmQOSbparms:pp 4675 2155 18000 - 12
This implies a forward acceptable peak-to-peak CDV of 8.125 ms, a
backward acceptable peak-to-peak CDV of 4.675 ms, forward
cumulative peak-to-peak CDV of 3.455 ms, a backward cumulative
peak-to-peak CDV of 2.155 ms, a forward acceptable maximum
cell transfer delay of 32 ms, a backward acceptable maximum
cell transfer delay of 18 ms, an unspecified forward cumulative
cell transfer delay, an unspecified backward cumulative cell transfer
delay, a forward cell loss ratio of
10 raised to minus 11 and a backward cell loss ratio of 10 to
the minus 12.
In certain applications (such as SIP-based applications), an SDP
descriptor might have both the atmQOSfparms and atmQOSbparms
attributes. In other applications (such as Megaco-based applications),
the remote descriptor can have the atmQOSfparms attribute
Rajesh Kumar, Mohamed Mostafa [Page 34]
while the local descriptor can have the atmQOSbparms attribute.
5.7.17 The 'aal2QOSfparms' and 'aal2QOSbparms' attributes
It is recognized that means of characterizing impairments in AAL2
packet streams are not clearly defined at this time. These AAL2 media
attributes will constructed along the line of the 'atmQOSfparms'
and 'atmQOSbparms' attributes.
5.7.18 The 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes
When present, the 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes
are used to indicate ATM traffic descriptor parameters in the
forward and backward directions respectively. See Section
2.3 for a definition of the terms 'forward' and 'backward'.
The 'atmFtrfcDesc' and 'atmBtrfcDesc' media attribute lines
are structured as follows:
a=atmFtrfcDesc:<clpLvl> <pcr><scr><mbs><cdvt><mcr><mfs><fd><te>
a=atmBtrfcDesc:<clpLvl> <pcr><scr><mbs><cdvt><mcr><mfs><fd><te>
If any of these parameters in these media attribute
lines is not specified, is inapplicable or is implied, then it is
set to "-".
The <clpLvl> (CLP level) parameter indicates whether the rates and
bursts described in these media
attribute lines apply to CLP
values of 0, (0+1). It can take on the following string values:
"0", "0+1" and "-". If rates and bursts for both <clpLvl> values are to
be described, then it is necessary to use two separate
media attribute lines for each direction in the same session
descriptor. If the <clpLvl> parameter is set to "-", then it
implies that the CLP parameter is not applicable. This is true
when the 'atmFtrfcDesc' or 'atmBtrfcDesc' attribute is used to
describe an AAL2
CID rather than an ATM VC connection.
The meaning, units and applicability of the remaining parameters
are per the ATMF TM 4.1 specification [6] and are
reiterated below:
PARAMETER MEANING UNITS APPLICABILITY
<pcr> PCR Cells/ CBR, rt-VBR, nrt-VBR,
second ABR, UBR, GFR;
CLP=0,0+1
<scr> SCR Cells/ rt-VBR, nrt-VBR;
second CLP=0,0+1
<mbs> MBS Cells rt-VBR, nrt-VBR,
GFR;
CLP=0,0+1
Rajesh Kumar, Mohamed Mostafa [Page 35]
<cdvt> CDVT Microsec. CBR, rt-VBR, nrt-VBR,
ABR, UBR, GFR;
CLP=0,0+1
<mcr> MCR Cells/ ABR,GFR;
second CLP=0+1
<mfs> MFS Cells GFR;
CLP=0,0+1
<fd> Frame "on"/"off" CBR, rt-VBR, nrt-VBR,
Discard ABR, UBR, GFR;
Allowed CLP=0+1
<te> CLP "on"/"off" CBR, rt-VBR, nrt-VBR,
tagging ABR, UBR, GFR;
Enabled CLP=0
<fd> indicates that frame discard is permitted. It can take on the string
values of "on" or "off". Note that, in the GFR case, frame discard
is always enabled. Hence, this subparameter can be set to "-" in
the case of GFR. Since the <fd> parameter is independent
of CLP, it is meaningful in the case when <clpLvl> = "0+1".
It should be set to "-" for the case when <clpLvl> = "0".
<te> (tag enable) indicates that CLP tagging is allowed.
These can take on the string values of "on" or "off".
Since the <te> parameter applies only to cells with
a CLP of 0, it is meaningful in the case when <clpLvl> = "0".
It should be set to "-" for the case when <clpLvl> = "0+1".
An example use of these media attribute lines for an rt-VBR,
single-CID AAL2 voice VC is:
a=atmFtrfcDesc:0+1 200 100 20 - - - on -
a=atmFtrfcDesc:0 200 80 15 - - - - off
a=atmBtrfcDesc:0+1 200 100 20 - - - on -
a=atmBtrfcDesc:0 200 80 15 - - - - off
This implies a forward and backward PCR of 200 cells per second
all cells regardless of CLP, forward and backward PCR of 200 cells
per second for cells with CLP=0, a forward and backward SCR of 100
cells per second for all cells regardless of CLP, a forward and
backward SCR of 80 cells per second for cells with CLP=0,
a forward and backward MBS of 20 cells for all cells regardless
of CLP, a forward and backward MBS of 15 cells for cells with
CLP=0, an unspecified CDVT which can be known by other means,
and an MCR and MFS which are unspecified because they are
inapplicable. Frame discard is enabled in both the forward and
backward directions. Tagging is not enabled in either direction.
In certain applications (such as SIP-based applications), an SDP
descriptor might have both the atmFtrfcDesc and atmBtrfcDesc
attributes. In other applications (such as Megaco-based applications),
the remote descriptor can have the atmFtrfcDesc attribute
Rajesh Kumar, Mohamed Mostafa [Page 36]
while the local descriptor can have the atmBtrfcDesc attribute.
5.7.19 The 'aal2FtrfcDesc' and 'aal2BtrfcDesc' attributes
It might be meaningful to construct descriptors for traffic
at the AAL2 packet (subcell) level. These can tentatively be
named the 'aal2FtrfcDesc' and 'aal2BtrfcDesc' attributes
When constructed, these can be similar in some aspects to the
'aal2FtrfcDesc' and 'aal2BtrfcDesc' attributes.
5.7.20 The 'abrFparms' and 'abrBparms' attributes
When present, the 'abrFparms' and 'abrBparms' attributes
are used to indicate the 'additional' ABR parameters specified
in the UNI 4.0 signaling specification [5]. These refer to the
forward and backward directions respectively. See Section
2.3 for a definition of the terms 'forward' and 'backward'.
The 'abrFparms' and 'abrBparms' media attribute lines
are structured as follows:
a=abrFparms:<nrm><trm><cdf><adtf>
a=abrBparms:<nrm><trm><cdf><adtf>
These parameters are mapped into the ABR service parameters in
[6] in the manner described below. These parameters can be
represented in SDP as decimal integers, with fractions permitted
for some. Details of the meaning, units and applicability of
these parameters are in [5] and [6].
If any of these parameters in the 'abrFparms' or 'abrBparms'
media attribute lines is not specified, is inapplicable or is implied,
then it is set to "-".
SDP ATMF SDP REPRESENTATION
PARAMETER EQUIVALENT
<nrm> NRM Decimal/hex equivalent of 3 bit field
<trm> TRM -ditto-
<cdf> CDF -ditto-
<adtf> ADTF Decimal/Hex equivalent of 10 bit field
In certain applications (such as SIP-based applications), an SDP
descriptor might have both the abrFparms and abrBparms
attributes. In other applications (such as Megaco-based applications),
the remote descriptor can have the abrFparms attribute
while the local descriptor can have the abrBparms attribute.
5.7.21 The 'clkrec' attribute
When present, the 'clkrec' attribute is used to indicate
the clock recovery method. This attribute is meaningful in the
case of AAL1 unstructured data transfer (UDT). The format of the
'clkrec' media attribute line is as follows:
a=clcrec: <clcrec>
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The <clcrec> field can take on the following string
values: "NULL", "SRTS" or "adaptive". These are defined in
ITU I.363.1 [10]. "NULL" indicates that the stream (e.g. T1/E1)
encapsulated in ATM is synchronous to the ATM network or
is retimed using slip buffers.
5.7.22 The 'fec' attribute
When present, the 'fec' attribute is used to indicate the use of
forward error correction. Currently, there exists a forward error
correction method defined for AAL1 in ITU I.363.1 [10]. The format of the
'fec' media attribute line is as follows:
a=fec: <fecEnable>
The <fecEnable> flag indicates the presence of absence of Forward
Error Correction. It can take on the string values of "NULL", "loss
sensitive" and "delay sensitive". An "NULL" value implies disabling
this capability. FEC can be enabled differently for delay-sensitive
and loss-sensitive connections.
5.7.23 The 'prtfl' attribute
When present, the 'prtfl' attribute is used to indicate the fill
level of partially filled cells. This is the number of non-pad payload
octets, not including any AAL SAR or convergence sublayer octets. For
example, in some AAL1 applications that use partially filled cells with
padding at the end, this attribute indicates the number of leading
payload octets not including any AAL overhead.
The format of the 'prtfl' media attribute line is as follows:
a=prtfl: <partialFill>
Here, <partialFill> can be expressed as a decimal (no prefix)
or hex (0x prefix) integer. In general, permitted values are integers
in the range 1 - 46 inclusive. However, this upper bound is
different for different adaptations since the AAL overhead is
different.
In the case of AAL1 SDT used for n x 64 (n>=2) clear channel
transmission,
this media attribute line applies to both P and non-P cells.
A value of 46 indicates no padding in P-cells and a padding of
one in non-P cells. If partial fill is enabled, structures
shall not be
split across cell boundaries and shall fit in any cell. Hence,
their size shall be less than or equal to the partial fill
size (maximum of 46). Further, the partial fill size is preferably
an integer multiple of the structure size. If not, then the
partial fill size stated in the SDP description shall be
truncated to an integer multiple (e.g. a partial fill size of
40 is truncated to 36 to support six 6 x 64 channels).
5.7.24 The 'bearertype' attribute
When present, the 'bearertype' attribute is used to indicate
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whether the underlying bearer is an ATM PVC/SPVC, an ATM SVC,
or an AAL2 CID connection within an existing ATM PVC/SPVC.
Additionally, for ATM SVCs and AAL2 CID connections, the
'bearertype' attribute can be used to indicate whether the
media gateway initiates connection set-up via bearer signaling
(Q.2931-based or Q.2630.1 based. The format of the 'bearertype'
media attribute line is as follows:
a=bearertype: <bearerType> <localInititiation>
The <bearerType> field can take on the following string values:
"PVC", "SVC", "CID", with semantics as defined above.
In the case when the underlying bearer is a PVC/SPVC, or a CID
assigned by the MGC rather than through bearer signaling, the
<localInititiation> flag can be omitted or set to "-". In the
case when bearer signaling is used, this flag can be omitted
when it is known by default or by other means
whether the media gateway initiates
the connection set-up via bearer signaling. Only when this is to
be indicated explicitly that the <localInititiation> flag takes
on the values of "on" or "off". An "on" value indicates that
the media gateway is responsible for initiating connection set-up
via bearer signaling (SVC signaling or Q.2630.1 signaling),
an "off" value indicates otherwise.
5.7.25 The 'structure' attribute
This attribute applies to AAL1 connections only. When present,
the 'structure' attribute is used to indicate the presence or
absence of structured data transfer (SDT), and the size in octets
of the SDT
blocks. The format of the 'structure' media attribute line is as
follows:
a=structure: <structureEnable> <blksz>
where the <structureEnable> flag indicates the presence of absence of SDT.
It can take on the values of "on" or "off". An "on" value implies
AAL1 structured data transfer (SDT), while an "off" value implies
AAL1 unstructured data transfer (UDT).
The block size field, <blksz>, is an optional 16-bit field (Q.2931)
that can be represented in decimal (no prefix) or in hex (0x prefix).
It can be omitted or set to a "-" when not applicable, as in the case
of unstructured data transfer (UDT). For SDT, it can be omitted or set
to a "-" when <blksz> is known by other means. For instance,
af-vtoa-78 [7] fixes the structure size for n x 64 service,
with or without CAS. The theoretical maximum value of <blksz> is 65,535,
although most services use much less.
5.7.26 The 'sbc' attribute
The 'sbc' media attribute line denotes the subchannel count and
is meaningful only in the case of n x 64 clear channel
communication. A clear n x 64 channel can use AAL1
(ATM forum af-vtoa-78) or AAL2 adaptation (ITU I.366.2). Although
no such standard definition exists, it is also possible to use
AAL5 for this purpose. An n x 64 clear channel is represented
Rajesh Kumar, Mohamed Mostafa [Page 39]
by the encoding names of "X-CCD" and "X-CCD-CAS" in
Table 1.
The format of the 'sbc' media attribute line is as follows:
a=sbc: <sbc>
Here, <sbc> can be expressed as a decimal (no prefix)
or hex (0x prefix) integer. This attribute indicates the
number of DS0s in a T1 or E1 frame that are aggregated for
transmitting clear channel data. For T1-based applications, it
can take on integral values in the inclusive range [1...24]. For
E1-based applications, it can take on integral values in the
inclusive range [1...31]. When omitted, other means are to be used
to determine the subchannel count.
5.7.27 The 'fcpssdusize' and 'bcpssdusize' attributes
When present, the 'fcpssdusize' and 'bcpssdusize' attributes are used to
indicate the maximum size of the CPCS SDU payload in the forward and
backward directions respectively. See section 2.3 for a definition of the
terms 'forward' and 'backward'.
The format of these media attribute line is as follows:
a=fcpssdusize: <cpcs>
a=bcpssdusize: <cpcs>
The <cpcs> fields is a 16-bit integer that can be
represented in decimal (no prefix)or in hex (0x prefix).
The meaning and values of these fields are as follows:
Application Field Meaning Values
AAL5 <cpcs> Maximum CPCS-SDU size 1- 65,535
AAL2 <cpcs> Maximum CPCS-SDU size 45 or 64
In certain applications (such as SIP-based applications), an SDP
descriptor might have both the fcpssdusize and bcpssdusize
attributes. In other applications (such as Megaco-based applications),
the remote descriptor can have the fcpssdusize attribute
while the local descriptor can have the bcpssdusize attribute.
5.7.28 The 'aal2CPS' attribute
When present, the 'aal2CPS' attribute is used to indicate
describe parameters associated with the AAL2 CPS layer.
The format of the 'aal2CPS' media attribute line is as
follows:
a=aal2CPS: <maxChan> <timerCU>
Each of these fields can be set to a "-" when the intention
is to not specify them in an SDP descriptor.
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The <maxChan> integer can take on values between 1 and 255.
It represents the number of channels (CIDs) multiplexed into
the AAL2 VCC. It can be represented in decimal (no prefix)
or in hex (0x prefix).
The <timerCU> integer represents the "combined use" timerCU
defined in ITU I.363.2. This timer is represented as an
integer number of microseconds.
5.7.29 The 'aal2_sscs_3661' attribute
When present, the 'aal2_sscs_3661' attribute is used to indicate
the presence of an AAL2 SSCS sublayer as defined in ITU I.366.1 [12].
Optionally, it can be used to indicate selected options and
parameter values for this SSCS.
The format of the 'aal2_sscs_3661' media attribute line is as
follows:
a=aal2_sscs_3661: <adt> <ted> <fsssar> <bsssar>
Each of these fields can be set to a "-" when the intention
is to not specify them in an SDP descriptor.
The <adt> flag indicates the presence of absence of assured data
transfer as defined in I.366.1. The <ted> flag indicates the
presence of absence of transmission error detection as defined
in I.366.1. Each of these flags can take on the values of "on"
or "off". An "on" value indicates presence of the capability.
The <fsssar> and <bsssar> fields are 16-bit integers that
can be represented in decimal (no prefix)or in hex (0x prefix).
The meaning and values of the <fsssar> and <bsssar> fields
are as follows:
Field Meaning Values
<fsssar> Maximum SSSAR-SDU size 1- 65,535
forward direction
<bsssar> Maximum SSSAR-SDU size 1- 65,535
backward direction
In certain applications (such as SIP-based applications), an SDP
descriptor might have an 'aal2_sscs_3661' media attribute line
with the <fsssar> and <bsssar> subparameters. In applications
(such as Megaco-based applications), the remote descriptor can have the
<fsssar> subparameter while the local descriptor can have the
<bsssar> subparameter.
5.7.30 The 'aal2_SSCS_3662' attribute
When present, the 'aal2_SSCS_3662' attribute is used to indicate
the presence of an AAL2 SSCS sublayer as defined in ITU I.366.2 [13].
Optionally, it can be used to indicate selected options and
parameter values for this SSCS.
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The format of the 'aal2_SSCS_3662' media attribute line is as
follows:
a=aal2_SSCS_3662: <sap> <circuitMode> <frameMode> <faxDemod>
<cas> <dtmf> <mfall> <mfr1> <mfr2>
<PCMencoding> <fmaxframe> <bmaxframe>
Each of these fields can be set to a "-" when the intention
is to not specify them in an SDP descriptor.
The <sap> field can take on the following string values: "audio"
and "multirate". These correspond to the audio and multirate
Service Access Points (SAPs) defined in ITU I.366.2.
The <circuitMode> flag indicates whether the transport of circuit
mode data is enabled or disabled, corresponding to the string
values of "on" and "off" respectively.
The <frameMode> flag indicates whether the transport of frame
mode data is enabled or disabled, corresponding to the string
values of "on" and "off" respectively.
The <faxDemod> flag indicates whether facsimile demodulation
and remodulation are enabled or disabled, corresponding to the
string values of "on" and "off" respectively.
The <cas> flag indicates whether the transport of Channel
Associated Signaling (CAS) bits in AAL2 type 3 packets is enabled
or disabled, corresponding to the string values of "on" and "off"
respectively.
The <dtmf> flag indicates whether the transport of DTMF dialled
digits in AAL2 type 3 packets is enabled or disabled, corresponding
to the string values of "on" and "off" respectively.
The <mfall> flag indicates whether the transport of MF dialled
digits in AAL2 type 3 packets is enabled or disabled, corresponding
to the string values of "on" and "off" respectively. This flag
enables MF dialled digits in a generic manner, without specifying
type (e.g. R1, R2 etc.).
The <mfr1> flag indicates whether the transport, in AAL2 type 3
packets, of MF dialled digits for signaling system R1 is enabled
or disabled, corresponding to the string values of "on" and "off"
respectively.
The <mfr2> flag indicates whether the transport, in AAL2 type 3
packets, of MF dialled digits for signaling system R2 is enabled
or disabled, corresponding to the string values of "on" and "off"
respectively.
The <PCMencoding> field indicates whether PCM encoding, if used,
is based on the A-law or the Mu-law. This can be used to qualify
the 'generic PCM' codec stated in some of the AAL2 profiles. The
<PCMencoding> field can take on the string values of "A"
and "Mu".
Rajesh Kumar, Mohamed Mostafa [Page 42]
The <fmaxframe> and <bmaxframe> fields are 16-bit integers that
can be represented in decimal (no prefix)or in hex (0x prefix).
The meaning and values of the <fmaxframe> and <bmaxframe> fields
are as follows:
Field Meaning Values
<fmaxframe> Maximum length of a 1- 65,535
frame mode data unit,
forward direction
<bmaxframe> Maximum length of a 1- 65,535
frame mode data unit,
backward direction
In certain applications (such as SIP-based applications), an SDP
descriptor might have an 'aal2_SSCS_3662' media attribute line
with the <fmaxframe> and <bmaxframe> subparameters. In applications
(such as Megaco-based applications), the remote descriptor can have the
<fmaxframe> subparameter while the local descriptor can have the
<bmaxframe> subparameter.
5.7.31 The 'aal2_sscs_3652' attribute
When present, the 'aal2_sscs_3652' attribute is used to indicate
the use, in conjunction with AAL2, of a service-specific
coordination function, as defined in ITU I.365.2 [40], for Connection
Oriented Network Service (SSCF-CONS). The format of the
'aal2_sscs_3652' media attribute line is as follows:
a=aal2_sscs_3652
5.7.32 The 'aal2_sscs_3653' attribute
When present, the 'aal2_sscs_3653' attribute is used to indicate
the use, in conjunction with AAL2, of a service-specific
coordination function, as defined in ITU I.365.3 [41], for Connection
Oriented Transport Service (SSCF-COTS). The format of the
'aal2_sscs_3653' media attribute line is as follows:
a=aal2_sscs_3653
5.7.33 The 'AAL5app' attribute
When present, the 'AAL5app' attribute is used to indicate
the presence of an application that uses AAL5, and to optionally
point to the
controlling standard for the application layer. The format of the
'AAL5app' media attribute line is as follows:
a=AAL5app: <AAL5app>
The <AAL5app> field can take on the string values listed
below, along with their meaning. Additionally, it can be set to "-"
if the controlling standard for the application is known by other
means such as by default or through provisioning.
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<AAL5app> Meaning
"h323c" Annex C of H.323 which specifies direct
RTP on AAL5 [45].
"af83" af-vtoa-0083.001, which specifies
variable size AAL5 PDUs with PCM voice
and a null SSCS [46].
"assuredSSCOP" SSCOP as defined in ITU Q.2110 [43],
assured operation.
"nonassuredSSCOP" SSCOP as defined in ITU Q.2110 [43],
non-assured operation.
"itu_i3651" Frame relay SSCS per ITU I.365.1 [39].
"itu_i3652" Service-specific coordination function,
as defined in ITU I.365.2, for Connection
Oriented Network Service (SSCF-CONS) [40].
"itu_i3653" Service-specific coordination function,
as defined in ITU I.365.3, for Connection
Oriented Transport Service (SSCF-COTS) [41].
"FRF11" Use of the FRF.11 frame relay standard
to transmit telephony payloads.
5.7.34 The 'lij' attribute
When present, the 'lij' attribute is used to indicate
the presence of a connection that uses the Leaf-initiated-join
capability described in UNI 4.0 [5], and to optionally describe
parameters associated with this capability. The format of the
'lij' media attribute line is as follows:
a=lij: <sci><lsn>
The <sci> (screening indication) is a 4-bit field expressed as a
decimal
or hex integer. It is defined in the UNI 4.0 signaling specification
[5]. It is expected that the values of this field will be defined
later by the ATMF and/or ITU. Currently, all values are reserved
with the exception of 0, which indicates a 'Network Join without Root
Notification'.
The <lsn> (leaf sequence number) is a 32-bit field expressed as a
decimal
or hex integer. Per the UNI 4.0 signaling specification [5], it is
used by a joining leaf to associate messages and responses during
LIJ (leaf initiated join) procedures.
Each of these fields can be set to a "-" when the intention
is to not specify them in an SDP descriptor.
5.7.35 The 'anycast' attribute
When present, the 'anycast' attribute line is used to indicate
the applicability of the anycast function described in UNI
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4.0 [5]. Optional parameters to qualify this function are
provided. The format of the 'anycast' attribute is:
a=anycast: <atmGroupAddress> <cdStd> <conScpTyp> <conScpSel>
The <atmGroupAddress> is per Annex 5 of UNI 4.0 [5]. Within
an SDP descriptor, it can be represented in one of the formats
(NSAP, E.164, GWID/ALIAS) described elsewhere in this document.
The remaining subparameters mirror the connection scope selection
information element in UNI 4.0 [5]. Their meaning and representation
is as shown below:
PARAMETER MEANING REPRESENTATION
<cdStd> Coding standard for the Decimal or hex
connection scope selection IE equivalent of
Definition: UNI 4.0 [5] 2 bits
<conScpTyp> Type of connection scope Decimal or hex
Definition: UNI 4.0 [5] equivalent of
4 bits
<conScpSel> Connection scope selection Decimal or hex
Definition: UNI 4.0 [5] equivalent of
8 bits
Currently, all values of <cdStd> and <conScpTyp> are reserved with
the exception of <cdStd> = 3 (ATMF coding standard) and <conScpTyp> = 1
(connection scope type of 'organizational').
Each of these fields can be set to a "-" when the intention
is to not specify them in an SDP descriptor.
5.7.36 The 'wtp' attribute
This is used for CALEA (lawful wiretap) conformance. It specifies the
VCC and/or CID to be used for delivering a tapped stream. An odd-even
convention is used.
The stream directed towards the tapped party (or towards a
party to which the tapped party's call is redirected) is copied into a
circuit with an even VCCI (if there are no CIDs or one CID per VCC) or a
circuit with an even CID (if there are multiple CIDs per VCC). VCCIs
used are 0,2,4... CIDs used are 8, 10, 12 ...
The stream from the tapped party (or from a
party to which the tapped party's call is redirected) is copied into a
circuit with the next odd VCCI (if there are no CIDs or one CID per VCC) or a
circuit with the next odd CID (if there are multiple CIDs per VCC). The odd
value in the pair is automatically derived by adding 1 to the even value and is
not specified in the 'wtp' attribute line. The resulting VCCI values are
1, 3, 5 ... The resulting CID values are 9, 11, 13 ...
This attribute has the following format:
a=wtp: <virtualConnectionId>
where <virtualConnectionId> is defined in sections above on the 'm' lines
for AAL1, AAL5 and AAL2. The wildcarding rules for <virtualConnectionId> are
applicable. Note that the semantics of the <virtualConnectionId> allow
specification of the ATM address of the remote delivery site.
Rajesh Kumar, Mohamed Mostafa [Page 45]
When SVC(s) are used for delivering the tapped streams
to another site, all terms in <virtualConnectionId> except the ATM address
of the remote delivery site are wildcarded.
5.7.37 Specification of Higher-layer attributes
This conventions in this ATM SDP document are limited to the ATM and adaptation
layers. Parameters associated with layers higher than the ATM adaptation
layer are addressed only if these are tightly coupled to the ATM or
adaptation layers.
ATM signaling standards provide 'escape mechanisms' to
represent, signal and negotiate higher-layer parameters. Examples
are the B-HLI and B-LLI IEs specified in ITU Q.2931 [15], and
the user-to-user information element described in ITU Q.2957 [48].
SDP as described in rfc2327 has a similar mechanism to
describe higher-layer parameters. This is the 'fmtp' or the
format-specific parameters attribute. This attribute is expressed in
the following manner:
a=fmtp:<format><format specific parameters>
It is suggested that applications use this attribute, described in
detail in rfc2327 [1], to express higher-layer parameters. Conventions
for the use of the 'fmtp' attribute to describe higher-layer information
are beyond the scope of the present document. However, it is recognized
that in some applications it is necessary to describe higher-layer
information within the same SDP descriptor as the ATM and AAL
information.
5.7.38 Use of the second media-level part in H.323 Annex C applications
Section 4 mentions that H.323 annex C applications have a second media level part
for the ATM session description. This is used to convey information about the RTCP
stream. Although the RTP stream is encapsulated in AAL5 with no intervening IP
layer, the RTCP stream is sent to an IP address and RTCP port. This media level
part has the following format:
m= <media> <port> <transport> <fmt list>
m= control <rtcpPortNum> H323c -
c= IN IP4 <rtcpIPaddr>
Consistency with rfc2327 is maintained in the location and format of these lines.
The <fmt list> is set o "-". The 'c' line in the second media-level part pertains
to RTCP only.
The <rtcpPortNum> and <rtcpIPaddr> subparameters indicate the port number and IP
address on which the media gateway is prepared to receive RTCP packets. Since this
refers to the RTCP packets and not to RTP packets, the port number is odd. If an
even port is specified, then the next odd number is used.
Any of the subparameters on these lines can be set to "-" if they are known by
other means.
The range and format of the <rtcpPortNum> and <rtcpIPaddr> subparameters is per
[1]. The <rtcpPortNum> is a decimal number between 1024 and 65535. It is an odd
number. If an even number in this range is specified, the next odd number is used.
The <rtcpIPaddr> is expressed in the usual dotted decimal IP address
representation, from 0.0.0.0 to 255.255.255.255, resulting in an alphanumeric
Rajesh Kumar, Mohamed Mostafa [Page 46]
string of 7 to 15 characters.
5.7.39 Chaining SDP descriptors
The start of an SDP descriptor is marked by a 'v' line. In some
applications, consecutive SDP descriptions are alternative descriptions
of the same session. In others, these describe different layers of the
same connection (e.g. IP, ATM, frame relay). This is useful when these
connectivity at these layers are established at the same time e.g. an
IP-based session over an ATM SVC. To distinguish between the
alternation and concatenation of SDP descriptions, a 'chain' attribute
can be used in the case of concatenation.
When present, the 'chain' attribute binds an SDP description to the
next or previous SDP description. The next or previous description is
separated from the current one by a 'v' line. It is not necessary that
this description also have a 'chain' media attribute line.
Chaining averts the need to set up a single SDP description for a
session that is simultaneously created at multiple layers. It allows
the SDP descriptors for different layers to remain simple and clean.
Chaining is not needed in the Megaco context, where it is possible to
create separate terminations for the different layers of a connection.
The 'chain' media attribute line has the following format:
a=chain: <chainPointer>
The <chainPointer> field can take on the following string values:
"next", "previous" and "NULL". The value "NULL" is not equivalent to
omitting the chain attribute from a description since it expressly
precludes the possibility of chaining. If the 'chain' attribute is
absent in an SDP description, chaining can still be realized by its
presence in the previous or next description.
6.0 List of Parameters with Representations
This section provides a list of the parameters used in this document,
and the formats used to represent them in SDP descriptions.
In the representations of these parameters, string values (including
single-character strings) are enclosed in double quotes (" ").
Decimal numbers are do not have a prefix, while hex numbers
are preceded by a 0x.
In general, a "-" value can be used for any field that
is not specified, is inapplicable or is implied.
PARAMETER MEANING REPRESENTATION
<username> User name Constant "-"
<sessionID> Session ID Decimal, Hex,
or Alphanumeric
At most 32 digits or
34 characters.
Rajesh Kumar, Mohamed Mostafa [Page 47]
<version> Version of Decimal or Hex
SDP descriptor At most 32 digits
<networkType> Network type Constant "ATM"
<ATMaddressType> ATM address type String values:
"NSAP", "E164", "GWID",
"ALIAS"
<ATMaddress> ATM address "NSAP": 40 hex digits,
optionally dotted
"E164": up to 15 decimal digits
"GWID": up to 32 characters
"ALIAS": up to 32 characters
<sessionName> Session name Constant "-"
<startTime> Session start Decimal or hex equivalent
time of 32-bit field
<stopTime> Session stop Constant "0"
time
<vcci> Virtual Circuit Decimal or hex equivalent
Connection of 16 bits
Identifier
<bcg> Bearer Connection Decimal or hex equivalent
Group of 8 bits
<portId> Port ID Decimal, Hex,
or Alphanumeric.
At most 32 digits or
34 characters.
<vpi> Virtual Path Decimal or hex equivalent
Identifier of 8 or 12 bits
<vci> Virtual Circuit Decimal or hex equivalent
Identifier of 16 bits
<vpci> Virtual Path Decimal or hex equivalent
Connection of 16 bits
Identifier
<cid> Channel Decimal or hex equivalent
Identifier of 8 bits
<payloadType> Payload Decimal integer 0-127
Type
<profileClass> Profile String values:
Class "ITU", "ATMF",
"custom", <corporateName>,
"IEEE:"<oui>
<oui>: IEEE-registered OUI
<profile> Profile Decimal integer 1-255
Rajesh Kumar, Mohamed Mostafa [Page 48]
<eecid> End-to-end Up to 8 hex digits
Connection
Identifier
<aalType> AAL type String values:
"AAL1","AAL1_SDT","AAL1_UDT",
"AAL2", "AAL3/4",
"AAL5", "User defined AAL"
<silenceSuppEnable> Silence suppression String values:
Enable "on", "off"
<silenceTimer> Kick-in timer Decimal or hex representation
for silence of 16-bit field
suppression
<suppPref> Preferred Silence String values:
Suppression Method "standard", "custom"
<sidUse> SID Use String values:
Method "No SID", "Fixed Noise",
"Sampled Noise"
<fxnslevel> Fixed Noise Decimal or hex representation
Level of a 7-bit field
<ecanEnable> Enable Echo String values:
Cancellation "on", "off"
<ecanType> Type of Echo String values:
Cancellation "G165", "G168"
<gcEnable> Enable Gain String values:
Control "on", "off"
<gcLvl> Level of inserted Decimal or hex equivalent
Loss of 16-bit field
<uuiCodeRange> UUI code range Decimal integer 0-15
<encodingName> Encoding name String values:
"PCMG", "SIDG", "SID729",
any value from column 2
of Table 1
<packetLength> Packet length Decimal integer 0-45
<packetTime> Packetization Decimal integer 1-500
Interval
<fxIncl> Facsimile included String values: "on", "off"
<asc> ATM service String values:
category defined "CBR", "nrt-VBR", "rt-VBR",
by the ATMF "UBR", "ABR", "GFR"
Rajesh Kumar, Mohamed Mostafa [Page 49]
<atc> ATM transfer String values:
capability "DBR","SBR","ABT/IT","ABT/DT",
defined by the "ABR"
ITU
<qosclass> QoS Class Decimal integer 0-5
<bcob> Broadband Bearer Decimal or hex representation
Class of 5-bit field
<stc> Susceptibility Decimal equivalent of
to clipping a 2-bit field
<upcc> User plane Decimal equivalent of
connection a 2-bit field
configuration
<cdvType> CDV type String values:
"pp", "2p"
<acdv> Acceptable CDV Integer or hex equivalent
of 24-bit field
<ccdv> Cumulative CDV Integer or hex equivalent
of 24-bit field
<actd> Acceptable CTD Integer or hex equivalent
of 16-bit field
<cctd> Cumulative CTD Integer or hex equivalent
of 16-bit field
<aclr> Acceptable Integer or hex equivalent
Cell Loss Ratio of 8-bit field
<clpLvl> CLP level String values:
"0", "0+1"
<pcr> Peak Cells/second
Cell Rate
<scr> Sustained Cells/second
Cell Rate
<mbs> Maximum Cells
Burst Size
<cdvt> CDVT Decimal integer or
fraction, range determined
by application.
<mcr> Minimum Cells/second
Cell Rate
<mfs> Maximum Cells
Frame Size
<fd> Frame Discard String Values:
Allowed "on", "off"
Rajesh Kumar, Mohamed Mostafa [Page 50]
<te> CLP tagging String Values:
Enabled "on", "off"
<nrm> NRM Decimal/hex equivalent
of 3 bit field
<trm> TRM - ditto-
<cdf> CDF -ditto-
<adtf> ADTF Decimal/Hex equivalent
of 10 bit field
<clcrec> Clock Recovery String values:
Method "NULL", "SRTS",
"adaptive"
<fecEnable> Forward Error String values:
Correction Enable "NULL", "loss sensitive"
"delay sensitive"
<partialFill> Partial Fill Decimal integer 1-46
or hex equivalent
<bearerType> Bearer Type String Values:
"PVC", "SVC", "CID"
<structureEnable> Structure Present String values:
"on", "off"
<blksz> Block Size Decimal or hexadecimal
equivalent of 16 bits
<sbc> Subchannel Count T1: Decimal integer 1-24
or hex equivalent
E1: Decimal integer 1-31
or hex equivalent
<cpcs> Maximum AAL5: Decimal or hex
CPCS SDU size equivalent of 16 bits
AAL2: 45 or 64
<maxChan> Maximum number of Decimal integer 1-255
subcell channels or hex equivalent
<timerCU> Timer, combined use Integer decimal; range
determined by application
<adt> Assured Data String values:
Transfer Enable "on", "off"
<ted> Transmission Error String values:
Detection Enable "on", "off"
<fsssar> Maximum SSSAR-SDU Decimal or hex
size, forward equivalent of 16-bit
direction field
Rajesh Kumar, Mohamed Mostafa [Page 51]
<bsssar> Maximum SSSAR-SDU Decimal or hex
size, backward equivalent of 16-bit
direction field
<sap> Service Access String values:
Point "audio", "multirate"
<circuitMode> Circuit Mode String values:
Enable "on", "off"
<frameMode> Frame Mode String values:
Enable "on", "off"
<faxDemod> Fax Demodulation String values:
Enable "on", "off"
<cas> Enable CAS transport String values:
via Type 3 packets "on", "off"
<dtmf> Enable DTMF transport String values:
via Type 3 packets "on", "off"
<mfall> Enable MF transport String values:
via Type 3 packets "on", "off"
<mfr1> Enable MF (R1) String values:
transport via "on", "off"
Type 3 packets
<mfr2> Enable MF (R2) String values:
transport via "on", "off"
Type 3 packets
<PCMencoding> PCM encoding String values:
" A", " Mu"
<fmaxframe> Maximum length of a Decimal or hex
frame mode data unit, equivalent of
forward direction 16-bit field
<bmaxframe> Maximum length of a -ditto-
frame mode data unit,
backward direction
<AAL5app> Application that uses String values:
AAL5 "h323c","af83",
"assuredSSCOP",
"nonassuredSSCOP",
"itu_i3651", "itu_i3652",
"itu_i3653", "FRF11"
<sci> Screening Indication Decimal or hex
equivalent of 4 bits.
<lsn> Leaf Sequence Number Decimal or hex
equivalent of 32 bits.
Rajesh Kumar, Mohamed Mostafa [Page 52]
<cdStd> Coding standard for the Decimal or hex
connection scope selection equivalent of
IE 2 bits
Definition: UNI 4.0 [5]
<conScpTyp> Type of connection scope Decimal or hex
Definition: UNI 4.0 [5] equivalent of 4 bits
<conScpSel> Connection scope selection Decimal or hex equivalent
Definition: UNI 4.0 [5] of 8 bits
<rtcpPortNum> RTCP port number for Odd decimal in range 1024 to
H.323 Annex C applications 65535
<rtcpIPaddr> IP address for receipt Dotted decimal, 7-15 chars
of RTCP packets
<chainPointer> Chain pointer String values: "next",
"previous", "NULL"
7.0 Examples of ATM session descriptions using SDP
An example of a complete AAL1 session description in SDP is:
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=audio $ AAL1/AVP 18 0 96
a=atmmap:96 G727-32
a=eecid:B3D58E32
An example of a complete AAL2 session description in SDP is:
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
a=eecid:B3E32
The AAL2 session descriptor below is the same as the one above
except that it states an explicit preference for a voice codec, a
voiceband data codec and a voiceband fax codec. Further, it defines
the profile AAL2/custom 100 rather than assume that the far-end is
cognizant of the elements of this profile.
Rajesh Kumar, Mohamed Mostafa [Page 53]
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
a=eecid:B3E32
a=profiledesc:AAL2/custom 100 0-7 PCMG 40 5 0-7 SIDG 1
5 8-15 G726-32 40 10 8-15 SIDG 1 5
a=vsel:G726-32 40 10
a=dsel:PCMU - -
a=fsel:G726-32 40 10
8.0 Representation of data media
The following encoding names in Table 1 can refer to data as well
as audio media: X-CCD and X-CCD-CAS in Table 1.
The following encoding names in Table 1 refer to data media:
X-FXDMOD-3 in Table 1.
In the AAL1 context, X-CCD and X-CCD-CAS can be represented as
"audio" codecs that are dynamically mapped into payload types. This
is done through the 'atmmap' attribute, as described earlier. For
example:
m=audio 27 AAL1/AVP 98
a=atmmap:98 X-CCD
implies that AAL1 VCCI=27 is used for n x 64 transmission.
Currently, AAL1 in unsuitable for transmitting demodulated facsimile
because it lacks the bearer plane mechanisms (equivalent to AAL2
type 3 messages) for transmitting control information.
In the AAL2 context, these "codecs" can be assigned profile types and
numbers. Even though it is not possible to construct
profile tables as described in ITU I.366.2 for these "codecs", it
is preferable to adopt the common AAL2 profile convention in their
case. An example AAL2 profile mapping for these could be as follows:
PROFILE TYPE PROFILE NUMBER "CODEC" (ONLY ONE)
"custom" 200 X-CCD
"custom" 201 X-FXDMOD-3
The profile does not identify the number of subchannels ('n' in nx64).
This is known by other means such as the 'sbc' media attribute line.
Currently, there is no definition of n x 64 trunking with CAS for AAL2.
For example, the media information line:
m=audio $ AAL2/custom 200
a=sbc:6
implies a 384 kbps n x 64 circuit using AAL2 adaptation.
Rajesh Kumar, Mohamed Mostafa [Page 54]
In the case of fax demodulation and remodulation (ITU
I.366.2), parameters such as information type, image data
size and control type are negotiated in the 'bearer plane'
via type 3 messages. There is no need to define
several encoding names for these control streams.
9.0 Security Considerations
9.1 Bearer Security
At present, standard means of encrypting ATM and AAL2 bearers
are not conventionalized in the same manner as means of encrypting RTP
payloads. Nor has the authentication of ATM or AAL2 bearer
signaling.
If and when an ATM or AAL2 bearer encryption convention is
conventionalized,
the SDP encryption key line (k=) defined in rfc2327 can be used
to represent the encryption key and the method of obtaining the
key. In the ATM and AAL2 contexts, the term 'bearer' can include
'bearer signaling' as well as 'bearer payloads'.
9.2 Security of the SDP description
The SDP session descriptions might originate in untrusted areas
such as
equipment owned by end-subscribers or located at end-subscriber
premises. SDP relies on the security mechanisms of the encapsulating
protocol or layers below the encapsulating protocol. Examples of
encapsulating protocols are the Session Initiation Protocol (SIP),
MGCP and Multimedia Gateway Control Protocol (MEGACO). No additional
security mechanisms are needed. SIP, MGCP and MEGACO
can use IPSec authentication as described in RFC1826 [Ref.
27]. IPSec encryption can be optionally used with authentication to
provide an additional, potentially more expensive level of security.
IPSec security associations can be made between equipment located in
untrusted areas and equipment located in trusted areas through
configured shared secrets or the use of a certificate authority.
10.0 Remaining Tasks
In the authors' opinion, the following tasks need to be done to
complete the definition of the basic conventions needed to describe
ATM connections in SDP.
- Adequate representation of AAL2 parameters, such as some of the
parameters found in Q.2630.1.
- Additional, detailed examples of the use of these SDP conventions.
- Address the so-called UBR+ service category. Where is it defined?
- Add a table of contents.
Rajesh Kumar, Mohamed Mostafa [Page 55]
References
[1] IETF RFC 2327, 'SDP: Session Description Protocol', April '98,
Mark Handley and Van Jacobson.
[2] IETF RFC 1889, 'RTP: A Transport Protocol for Real-Time
Applications', Jan. 1996.
[3] IETF RFC 1890, 'RTP Profile for Audio and Video Conferences
with Minimal Control', Jan. 1996.
[4] ATMF UNI 3.1 Specification, af-uni-0010.002. Of special
interest for this document is Section 5.4.5.5, ATM Adaptation
Layer Parameters.
[5] ATMF UNI 4.0 Signaling Specification, af-sig-0061.000.
[6] ATMF Traffic Management Specification, Version 4.1, af-tm-
0121.000.
[7] ATMF Circuit Emulation Service (CES) Interoperability
Specification, version 2.0, af-vtoa-0078.000, Jan. 97.
[8] ATMF Voice and Telephony over ATM - ATM Trunking using AAL1 for
Narrowband Services, version 1.0, af-vtoa-0089.000, July 1997.
[9] ATMF Specifications of (DBCES) Dynamic Bandwidth Utilization -
in 64kbps Timeslot Trunking over ATM - using CES, af-vtoa-
0085.000, July 1997.
[10] ITU-T I.363.1, B-ISDN ATM Adaptation Layer Specification: Type
1 AAL, August 1996.
[11] ITU-T I.363.2, B-ISDN ATM Adaptation Layer Specification: Type
2 AAL, Sept. 1997.
[12] ITU-T I.366.1, Segmentation and Reassembly Service Specific
Convergence Sublayer for AAL Type 2, June 1998.
[13] ITU-T I.366.2, AAL Type 2 Reassembly Service Specific
Convergence Sublayer for Trunking, Feb. 99.
[14] Draft ietf-avt-telephone-tones-05.txt, RTP payloads for
Telephone Signal Events, S.B.Petrack, Nov. 17, 1998.
[15] ITU-T Q.2931, B-ISDN Application Protocol for Access Signaling.
[16] Amendment 1, 2, 3 and 4 to ITU-T Q.2931, B-ISDN Application
Protocol for Access Signaling.
[17] SAP: Session Announcement Protocol , draft-ietf-mmusic-sap-v2-
04.txt, Mark Handley, Colin Perkins and Edmund Whelan .
[18] rfc2543, Handley, M., H. Schulzrinne , Schooler, E. and
Rosenberg, J., "Session Initiation Protocol (SIP)", March
1999.
Rajesh Kumar, Mohamed Mostafa [Page 56]
[19] rfc1349, Type of Service in the Internet Protocol Suite. P.
Almquist. July 1992.
[20] rfc2474, Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers. K. Nichols, S. Blake, F.
Baker, D. Black. December 1998.
[21] ITU-T I.363.5, B-ISDN ATM Adaptation Layer Specification: Type
5 AAL, Aug. 1996.
[22] ATMF PNNI 1.0, af-pnni-0055.000, March 1996.
[23] ietf-avt-rtp-new-05.txt, Oct. 21, 1999, RTP: A Transport
Protocol for Real-Time Applications.
[24] ietf-avt-profile-new-07.txt, Oct. 21, 1999, RTP Profile for
Audio and Video Conferences with Minimal Control.
[25] Media Gateway Control Protocol (MGCP), Mauricio Arango, Isaac
Elliott, Christian Huitema, Scott Pickett, Version 1.0,
RFC2705.
[26] draft-ietf-Megaco-merged-00.txt, April, 2000, Media Gateway
control (Megaco) protocol, Fernando Cuervo, Nancy Greene, Christian
Huitema, Abdallah Rayhan, Brian Rosen, John Segers.
[27] IP Authentication Header, R. Atkinson, August 1995, RFC1826.
[28] ITU I.371, Traffic Control and Congestion Control in the BISDN.
[29] ITU E.191, BISDN Numbering and Addressing.
[30] ATM Forum Addressing: Reference Guide, af-ra-0106.000.
[31] http://www.isi.edu/in-notes/iana/assignments/rtp-parameters
for a list of codecs with static payload types.
[32] ITU Q.2941-2, Digital Subscriber Signalling System No. 2
(DSS 2): Generic identifier transport extensions.
[33] ITU Q.2961, Digital subscriber signalling system no.2 (DSS 2)
- additional traffic parameters. Also, Amendment 2 to Q.2961.
[34] ITU Q. 2965.1, Digital subscriber signalling system no.2 (DSS 2)
- Support of Quality of Service classes.
[35] ITU Q. 2965.2, Digital subscriber signalling system no.2 (DSS 2)
- Signalling of individual Quality of Service parameters.
[36] ITU Q.1901, Bearer Independent Call Control Protocol.
[37] ITU Q.2630.1, AAL type 2 signaling protocol - capability set 1.
[38] ITU I.363.5, B-ISDN ATM Adaptation Layer specification: Type 5
AAL.
[39] I.365.1,Frame relaying service specific convergence sublayer
(FR-SSCS).
Rajesh Kumar, Mohamed Mostafa [Page 57]
[40] I.365.2, B-ISDN ATM adaptation layer sublayers: service
specific coordination function to provide the connection
oriented network service.
[41] I.365.3, B-ISDN ATM adaptation layer sublayers: service
specific coordination function to provide the
connection-oriented transport service.
[42] I.365.4, B-ISDN ATM adaptation layer sublayers: Service specific
convergence sublayer for HDLC applications.
[43] Q.2110, B-ISDN ATM adaptation layer - service specific connection oriented
protocol (SSCOP).
[44] af-vtoa-0113.000, ATM trunking using AAL2 for narrowband services.
[45] H.323-2, Packet-based multimedia communications systems.
[46] af-vtoa-0083.000, Voice and Telephony Over ATM to the Desktop.
[47] I.356, BISDN ATM layer cell transfer performance.
[48] ITU Q.2957, Digital Subscriber Signaling System No. 2, User to user
signaling.
[49] rfc1305, Network Time Protocol, version 3.
Acknowledgements
The authors wish to thank several colleagues at Cisco and in the
industry who have contributed towards the development of these SDP
conventions, and who have reviewed, implemented and tested these
constructs. Valuable technical ideas that have been incorporated
into this internet draft have been provided by Hisham Abdelhamid,
David Auerbach, Robert Biskner, Bruce Buffam, Steve Casner, Alex Clemm,
Bill Foster, Snehal Karia, Raghu Thirumalai Rajan, Joe Stone, Bruce
Thompson, Dan Wing and Ken Young of Cisco, Michael Brown, Rade
Gvozdanovic, Graeme Gibbs, Tom-PT Taylor and Sophia Scoggins of
Nortel Networks, Brian Rosen, Tim Dwight and Michael Mackey
of Marconi, Ed Guy and Petros Mouchtaris of Telcordia, Christian
Groves of Ericsson, Charles Eckel of Vovida Networks, Tom Jepsen of
Fujitsu and Mahamood Hussain of Hughes Software Systems.
The authors also wish to thank the ISC device control group,
and the MMUSIC and MEGACO subgroups of the IETF, especially Bill Foster,
Jeorg Ott and Brian Rosen for their help in the preparation of this
document.
If there are names of contributors that have been overlooked, please
let the authors know before the document goes on standards track.
Rajesh Kumar, Mohamed Mostafa [Page 58]
Authors' Addresses
Rajesh Kumar
Cisco Systems, Inc.
M/S SJC01/3
170 West Tasman Drive
San Jose, CA 95134-1706
Phone: 1-800-250-4800
Email: rkumar@cisco.com
Mohamed Mostafa
Cisco Systems, Inc.
M/S SJC01/3
170 West Tasman Drive
San Jose, CA 95134-1706
Phone: 1-800-250-4800
Email: mmostafa@cisco.com
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Rajesh Kumar, Mohamed Mostafa [Page 59]
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