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INTERNET DRAFT
May 24, 1999.                                  Vikas Bajaj
Expires on November 24,1999.                   Sandip Ranjhan
<draft-hss-megaco-R2package-02.txt>            Prashant Jain
                                               Madhu Babu

                R2 Package for MEGACO Protocol


Status of this document

This doucment is a Internet-Draft and is in full conformance with all
provisions of section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas,and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.


Internet-Drafts are draft documents valid for a maximum of six months
 and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.




Abstract

This document  defines a R2 package in association with the MEGACO
Protocol that can be used to control a Media Gateway (MG) from an
external controller, called a Media Gateway controller (MGC).

The document is organised into the following major sections:

* Introduction to R2 signalling

* Definition of R2 package with brief description of the Events and
signals in the package.

* Different call flow scenarios where R2 signalling is used on either
one end or both ends. Scenarios with multiple MGCs are also
considered.


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Table of contents.

1.0 Introduction............................................... 3

    1.1  Introduction to R2 singalling......................... 3

2.0 R2 package................................................  3

    2.1 Incoming R2 and Outgoing Residential GW under single MGC..8

    2.2 Incoming Residential Gateway and Outgoing R2
         Gateway under single MGC..............................14

    2.3 Incoming R2 Gateway and Outgoing H.323 terminal
         under single MGC................................... ..22

    2.4 Incoming H.323 terminal and Outgoing R2 Gateway
         under single MGC..................................... 27

    2.5  Call flows with 2 MGCs................................32

         2.5.1 Incoming R2 and Outgoing Residential Gateway
           under different MGC.................................32

         2.5.2 Incoming R2 GW and outgoing SS7 GW, under
               different MGC...................................40

3.0 Conclusions................................................45

4.0 References.................................................46

5.0 AuthorÆs address...........................................46





















Vikas,Sandip,Prashant,Madhu                                [Page2]






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1.0 Introduction

This document describes the R2 package in association with MEGACO
protocol for controlling Media Gateways from external call control
elements called Media Gateway Controllers.



1.1 Introduction to R2 signalling

R2 signalling is used as an international signalling system within
international regions, and for integrated international/national
signalling. It's suitable for both automatic and semiautomatic
working. It allows for rapid call set-up and provides sufficient
signals in both directions to permit the transmission of numerical
and other information relating to the called and calling subscribers
lines and to increase routing facilities.

The interregister signalling is a compelled multifrequency code
system. Line signalling uses an out-band low-level tone-on-idle
signalling method for analogue working.


Interregister signalling is performed end-to-end using a 2-out-of-6
in-band mulitfrequency code with forward and backward compelled
signalling. The register signalling is faster as there is no signal
regeneration in intermediate exchanges. Overlap operation of address
signalling makes it faster than R1 or decadic. The following
operational features are provided using multifrequency code:

    - Calling party number identification
    - Calling party category identification
    - Nature of the circuit
    - Reason for Call failure
    - Language digits for international calls
    - Forward and backward signals for control of echo suppressers
to name a few.

2.0 R2-package

The Media Gateway Control Protocol (MEGACOP) organises the
communication between the Media Gateway Controller (MGC) and the
Media Gateway (MG) assuming a distributed call control architecture.
MEGACOP is defined in document [1].

The connection model for the MEGACO protocol is described using just
two abstractions, Terminations and Contexts. Terminations (T) are
entities representing physical endpoints, such as analogue loops or
timeslots on a TDM channel, as well as more ephemeral representations
of flow terminations, such as RTP streams.




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Membership in a Termination class determines the capabilities of a
Termination. Termination capabilities include events and signals that
a Termination supports. These are grouped into packages. The list of
Events and signals applicable for a Termination class must thus be
defined by the list of applicable Event Packages.

The signalling used between interoffice trunks might be pulse
dialing, E and M, R1 or R2. For R2 signalling, a specific set of
events and signals must be defined so that the MGC will command MG
using MEGACO Commands and MG will notify the requested events to the
MGC. But lack of events and signals related to R2 signalling system
like, calling party category, reason for failure of call set-up etc,
forced to define the R2 package.

This draft defines an "R2 package" which is used to describe variety
of call flows assuming R2 signalling at one/both ends of the Gateway.


Considering the situation where R2 signalling is being employed at
one end of the Gateway, then the Gateway has to terminate R2
signalling at that end and originate another type of signalling, as
required at the other end. Moreover, if both the incoming and
outgoing ends uses R2 signalling then the end-to-end register
signalling of R2 is not possible. Gateway should in that case
terminate R2 signalling at incoming end and originate R2 signalling at the outgoing end.


In all the call flows featuring the use of R2 package, other packages
defined in [1], for example Trunk package for DS0 terminations, Line
package for analogue terminations, etc,
have been used.


It is assumed that the compelled sequence generation which is a key
part of R2 signalling, is done at the Media Gateway without having
any intervention from the MGC. The basic events and signals have been
used from packages defined in [1].


These call flows are solely meant to exhibit the behaviour of the
Megaco protocol with R2 signalling at one or both ends. Moreover it
also signifies the necessity of R2 package. The events and signals in
R2 package are listed below









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Package name: R2

---------------------------------------------------------------------
   Symbol   |  Definition         |      R    |    S    |Duration
---------------------------------------------------------------------
    sz      |Seizure              |     X    |     OO   |
    di      |Destination Number   |     X    |     TO   |
    si      |Source Number        |     X    |     TO   |
    sa      |Seizure Acknowledgement    X    |     OO   |
    clr     |Clear (Back/Forward) |     X    |     OO   |
    sc      |Subscriber category  |     X    |     TO   |
    un      |Unallocated Number   |     X    |          |
    nn      |No number tone       |          |     OO   |
    spl     |SIT tone             |          |     OO   |
    slb     |Subscriber line busy |     X    |          |
    bt      |Busy tone            |          |     OO   |
    slf     |Subscriber line free |     X    |          |
    ct      |Congestion National/Intl   X    |          |
    soo     |Subscriber out of order    X    |          |
    of      |Report Failure       |     X    |          |
---------------------------------------------------------------------

The definition of the R2 package events and their intention of
inclusion are discussed as follows:

Seizure
    It indicates the incoming indication of call attempt.

Destination number
     Used to collect called party information at incoming Gateway
and to signal it to the outgoing Gateway. There will be a Digit map
associated with the termination, which will decide the number plan
for collecting specified number of digits. At the incoming end, the
destination party digits are collected using Digit map and sent to
the MGC as string. In the case of R2, the number has to be signalled
from the MGC to MG to assist compelled sequence generation.

Source Number
    Used to collect and signal calling party number. The reason of
this event inclusion is same as that of destination number.

Seizure Acknowledge
    Acknowledgement for seizure. Its even possible that whenever
Seizure acknowledge is sent the MGC may command MG to start
collecting the digits.

Clear
    To indicate the end of call (both successful and unsuccessful).
Since the intention of clearback or clearforward is to terminate the
call, both these functionalities are achieved by "clear".



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Subscriber category
    In R2 signalling, there is provision for indicating the
priority of the subscriber. The subscriber category is assumed to be
string.

Unallocated Number
    Event to indicate unallocated number/ numbe r unassigned.
Required for indicating reason for call failure.

Subscriber Line busy
    Indicates a valid number but subscriber is engaged in some
other call.

Busy tone
    Required giving unsuccessful call indication to the calling
user. Since the presence of gateway will make the end-to-end R2
signalling to link-to-link, the remote R2 exchanges indication of
call failure indicating that called subscriber is busy.

No circuit tone
    This tone is used as a signal in response to the event
congestion on national/international lines.

SIT tone
    This tone is used as special information tone, as its required
for R2 signalling.

Subscriber line free
    To indicate the MGC that the called subscriber is free, and the
calling user can be alerted.

Congestion national/international
    To indicate congestion condition on an outgoing R2 trunk.
Required indicating the reason for call failure.

Subscriber line out of order
    To indicate the MGC that the call failed because the subscriber
line was out of order.


For some of the events described in the package, the mapping of event
to actual frequency is configured at MG, as the value may differ due
to country variants. As mentioned earlier the compelling for address
signalling is done at MG. Since according to MEGACOP the function of
MG is to collect digits according to digit map and sends to the MGC
enbloc so, this functionality is confined to MG. If compelling is
done under supervision of the MGC then the call control at the MGC
becomes very complex, as there may be too many country variants.






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The following figure shows a typical example, how compelling is done.

----------------------------------------------
    R2  |    MG
        |
------------------------------------------------
Called party|
First digit------------->
        |
    <------------ A5 (send calling party category)
        |
calling party|
category ------------->
        |
    <-----------A1 (send next digit)
        |
        :
        :
        :     Destination number collected.
    <------------A9(Send calling party category)
        |
calling party|
First digit---------->
        |
    <-----------A1 (send next digit)
        :
        :
        :
    <-----------A6 (Address complete, charge, and set-up speech
                   conditions)
            or A3 (Address complete, change to Group B)
------------------------------------------------

In all the flows in the following sections even though it is not
explicitly shown, it is assumed that a digit map is associated when
the MGC commands MG to collect called and calling party numbers. The
text description given for each of the call flow presents a
description of the commands that are exchanged between MG and MGC.
The text doesn't strictly follow the EBNF notation but gives some
idea of parameter that are passed.













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2.1 Incoming R2 and Outgoing Residential GW under single MGC.

---------------------------------------------------------------------
    R2      |           MG    |        MGC            |      RGW
            |                 |                       |
---------------------------------------------------------------------
            |                 |Modify(T1) EL: sz      |
            |           <----------                   |
            |                 |                       |
            |           Resp (ok)------------>        |
            |                 |                       |
Seizure     |    Notify (sz)--------->                |
            |                 |                       |
            |<---------Resp (ok)                      |
            |                 |                       |
            |              <------------Modify (T1)   |
            |            SL: sa EL: di, si, sc, clr   |
            |                 |                       |
            |        Resp (ok)------------>           |
      <----------Seizureack   |                       |
            |                 |                       |
          Script will         |                       |
        Collect Digits        |                       |
            |                 |                       |
     <----------A6            |                       |
            |                 |                       |
            |    Notify (di, si, sc)-------->         |
            |                 |                       |
            |       <------------Resp (ok)            |
            |                 |                       |
            |         <-----------Add (T1)            |
            |                 |                       |
            |   Resp (ok)------------>                |
            |                 |                       |
            |                 |                 Add (T2)------->
            |                 |                       |
            |                 |                 <-----------Resp (ok)
            |                 |                       |
            |                 |          Modify (T2)------------>
            |                 |                       |
            |                 |           EL: hd  SD:l/rg
            |                 |                       |
            |                 |                 <-----------Resp (ok)
            |                 |                       |
            |      <--------------Modify (T1), RD     |
            |               SL: G/rt                  |
            |                 |                       |
            |    Resp(ok)------------->               |
            |                 |                       |
            |                 |                       |    Off-hook
            |                 |                   <---------Notify
            |                 |                       |
            |                 |            Resp(ok)----------->

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            |                 |                       |
            |                 |         Modify(T2)------------>
            |                 |           EL: hu      |
            |                 |                       |
            |                 |            <-----------Resp(ok)
            |                 |                       |
            |         <-------------Modify(T1)        |
            |                 |  mode=sendrecv        |
            |                 |  SD:{T/as}            |
            |         Resp(ok)---------->             |
            |                 |                       |
     ________________________________________________________________
                             MEDIA
     ________________________________________________________________
            |                 |                       |      On-hook
            |                 |                     <---------Notify
            |                 |                       |
            |                 |                 Resp(ok)------------>
            |                 |                       |
            |        <-------------Subtract(T1)       |
            |                 SL:clr                  |
            |                 |              subtract(T2)----------->
            |                 |                       |
            |                 |                       |
            |     Resp(ok)-------->           <---------- Resp(ok)
            |                 |                       |
_____________________________________________________________________


The figure above depicts the call flow describing call connection
between an incoming R2 Gateway and an outgoing residential Gateway.
For exchange of information from MGC to MG, MEGACOP is used by the
MGC (Media Gateway Controller) to control the two endpoints located
on the two Media Gateways. The first command is the MODIFY command
sent by the MGC to the R2 Gateway. The request will consist of the
following lines.

TRANS 12345678 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/*
ED= {R2/sz}

The above text indicates that MG is requested to check for seizure
signal on all the incoming R2 terminations "Trunkgroup-1/*". Since
the terminations are out of context the CTX value is set to NULL. The
response from MG would be of following form








Vikas,Sandip,Prashant,Madhu                                 [Page9]





INTERNET-DRAFT              R2 package                May 24,1999



ACPT 12345678 MG1.network.com: 12354 MEGACOP 1.0
CTX= NULL
MODIFY=Trunkgroup-1/*

After having noticed seizure on a particular termination, MG will
send a NOTIFY command to the MGC:

TRANS 12345679 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6
OE= {R2/sz}

The following RESPONSE will be sent back to MG:

ACPT 12345679 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6

After having noticed the incoming seizure, the MGC will send a MODIFY
command to send a seizure acknowledgement and to collect called and
calling party digits by passing the Digit map and also requests for
calling party category. To check for the originating user going
"onhook", an event "clear" is also included in the event list:



TRANS 12345680 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/6
ED= {R2/di,
R2/si, R2/sc, R2/clr}
SD= {R2/sa}

MG after having received the above MODIFY command sends response to
the MGC as:

ACPT 12345680 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/6

After sending seizure acknowledgement, MG invokes a script to do
compelled sequence for the collection of calling and called party
digits according to the digit map. After accumulating all the digits,
it sends a NOTIFY command to the MGC:

TRANS 12345681 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6
OE= {di, si, sc}




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RESPONSE will be sent back to MG as:

ACPT 12345681 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6

After receiving this response, the MGC instructs the incoming R2 MG
to add the specified termination to context using ADD command as:


TRANS 12345682 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=Trunkgroup-1/6
LS={m=recvonly}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.100.89
m=audio ANY RTP/AVP 0
}

In the response of the above ADD command, MG will give the session
description of the local termination as well as the contextID.

ACPT 12345682 MG1.network.com: 12354 MEGACOP 1.0
CTX = C1
ADD=Trunkgroup-1/6
ADD= RTP/177
LT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}
Then MGC requests the outgoing residential gateway to add the called
termination to context using ADD command as:

TRANS 12345683 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=circuit1/5
LS={m=sendrecv}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.200.89
m=audio ANY RTP/AVP 0
}
RT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}




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For the above ADD command, RESPONSE is sent back by Residential MG
as:

ACPT 12345683 MG1.network.com: 12354 MEGACOP 1.0
CTX = C1r
ADD=circuit1/5
ADD= RTP/1177
LT= {v=0
c=IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}

After getting this response, a MODIFY command is sent from the MGC
to the residential media gateway for sending a ringtone to the called
user and check for the "offhook" event. The following would be sent:

TRANS 12345684 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1r
MODIFY=circuit1/5
ED= {L/hd}
SD= {L/rg}

RESPONSE to the above MODIFY command will be sent by MG as:

ACPT 12345684 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1r
MODIFY=circuit1/5

"Ringback" tone is sent from MGC to the incoming MG using MODIFY.
It also contains the Remote Descriptor of the ephemeral termination
at the outgoing residential gateway.

TRANS 12345685 MGC1.network.com: 12354 MEGACOP 1.0
CTX = C1
MODIFY= Trunkgroup-1/6
SD= {G/rt}
RT= {v=0
c=IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}

For the above MODIFY command RESPONSE is sent by R2 MG as:

ACPT 12345685 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6


When the destination user goes "offhook" MG NOTIFY the MGC as
follows:


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TRANS 12345686 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
NOTIFY=circuit1/5
OE= {L/hd}

RESPONSE will be sent by the MGC for this NOTIFY command as:


ACPT 12345686 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1r
NOTIFY=circuit1/5

When the MGC gets NOTIFY for destination user going "offhook", it
informs the incoming MG to make the mode to "sendrecv" and sends the
"answer supervision" signal which also stops the "ringback tone".

TRANS 12345687 MGC1.network.com: 12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6
LS= {m=sendrecv}
SD={T/as}
The following response comes at the MGC.

ACPT 12345687 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6

 At the same time the destination residential Gateway is informed to
notify the end user going  "onhook" using the MODIFY command as:

TRANS 12345688 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
MODIFY=circuit1/5
ED= {L/hu}

MG will send RESPONSE as follows

ACPT 12345688 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1r
MODIFY=circuit1/5

Media transfer takes place between the two until any of the user goes
on hook. It is assume that the called party goes "onhook". This event
is notified to the MGC as:

TRANS 12345689 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1r
NOTIFY=circuit1/5
OE= {L/hu}






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RESPONSE will be sent by the MGC as follows

ACPT 12345689 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1r
NOTIFY=circuit1/5

The two RTP terminations are then subtracted from the context by
respective MGs on the command of the MGC as:


TRANS 12345690 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
SUBTRACT=circuit1/5

MG will send RESPONSE as follows

ACPT 12345690 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1r
SUBTRACT=circuit1/5



At the incoming end, when the MGC sends SUBTRACT message to MG, it
adds a signal list which indicates MG to send a "clear" signal for
deallocation of resources and then subtract the termination from the
specified context as:

TRANS 12345691 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1
SUBTRACT=Trunkgroup-1/6
SD= {R2/clr}

MG will send RESPONSE as follows

ACPT 12345691 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1
SUBTRACT=Trunkgroup-1/6

Both Gateways at this point are ready for the next call.


2.2 Incoming Residential Gateway and Outgoing R2 Gateway under single
MGC.

---------------------------------------------------------------------
      RGW   |           MGC     |   MG             |       R2GW
            |                   |                  |
---------------------------------------------------------------------
          Modify(T1) EL:hd (EM SD:l/dl)            |
   <----------                  |                  |



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            |                   |                  |
      Resp(ok)------>           |                  |
            |                   |                  |
            |                   |                  |
Offhook     |                   |                  |
Notify(hd)------>               |                  |
            |                   |                  |
      <---Resp(ok)              |                  |
            |                   |                  |
 <------Modify(T1)              |                  |
            |EL:di,hu           |                  |
            |                   |                  |
  Resp(ok) -------->            |                  |
 Collection of                  |                  |
digits done here                |                  |
            |                   |                  |
Notify(di)---------->           |                  |
            |                   |                  |
      <-------Resp(ok)          |                  |
            |                   |                  |
      <--------Add(t1)          |                  |
            |                   |                  |
      Resp(ok)-------->         |                  |
            |                   |                  |
            |               Add(T2)------->        |
            |                   |                  |
            |          <------------Resp(ok)       |
            |                   |                  |
            |    Modify(T2)------------>           |
            | SL:sz ED:sa       |                  |
            |             <------------Resp(ok)    |
            |                   |                  |   Seizure---->
            |                   |                  |   Seizureack<---
            |                   |                  |
            |      <--------------Notify(T2)       |
            |                  OE: sa              |
            |                   |                  |
            | Resp(ok)------------->               |
            |                   |                  |
            |     Modify(T2)-------->              |
            |         SD: si,di                    |
            |     EL: soo,un,slb,slf,              |
            |       <-------Resp(ok)               |
            |                 |                    |Compelled digits
            |                 |                    | sent
            |            <---------Notify          |
            |                 |  (slf)             |
            |                 |                    |
            |          Resp(ok)----------->        |




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            |                 |                    |
   <------Modify(T1),RD       |                    |
         SL: G/rt             |                    |
            |                 |                    |
Resp(ok)--------->            |                    |
            |     Modify(T2)------------>          |
            |     ED: {T/as(EM:clr)}               |
            |                 |                    |
            |        <-----------Resp(ok)          |
            |                 |                    |  Answer
            |         <-------------Notify(T2)     |
            |                 |    (Answer)        |
            |                 |                    |
            |         Resp(ok)---------->          |
      <--------Modify(T1)     |                    |
            |  mode=sendrecv  |                    |
            |                 |                    |
Resp(ok)------->              |                    |
     ________________________________________________________________
                MEDIA
     ________________________________________________________________
            |                 |                    |      Clearback
            |      <-------------Notify clr        |
            |                 |                    |
            |   Resp(ok)------------>              |
            |                 |                    |
   <-------------Subtract(T1) |                    |
            |           subtract(T2)----------->   |
            |                 |                    |
            |                 |                    |
      Resp(ok)-------->       |         <-------------Resp(ok)
            |                 |                    |
_____________________________________________________________________




Here, the first command is the MODIFY command sent by the MGC to the
Residential Gateway. The modification request will consist of the
following lines.

TRANS 12345678 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=circuit1/*
ED= { L/hd, EM SD:l/dl}

The above text indicates that MG is requested to check for "Offhook"
on any of  the terminations "circuit1/*" on the Residential Gateway.
Since the terminations are out of context the CTX value is set to
NULL. The response from MG would be of following form



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ACPT 12345678 MG1.network.com: 12354 MEGACOP 1.0
CTX= NULL
MODIFY=circuit1/*

After having noticed "Offhook" on a particular termination, MG will
send a NOTIFY command to the MGC:

TRANS 12345679 MG1.network.com:12354 MEGACOP 1.0
CTX = NULL
NOTIFY=circuit1/6
OE= {L/hd}

The following RESPONSE will be sent back to MG:

ACPT 12345679 MGC1.network.com:12354 MEGACOP 1.0
CTX = NULL
NOTIFY=circuit1/6

After receiving this response, the MGC will send a MODIFY command
requesting to check a "Onhook" event on "circuit1/6" and to collect
called digits by passing the Digit map.

TRANS 12345680 MGC1.network.com:12354 MEGACOP 1.0
CTX = NULL
MODIFY=circuit1/6
ED= {D/[0-9 #T]

MG after having received the above MODIFY command sends response to
the MGC as:

ACPT 12345680 MG1.network.com:12354 MEGACOP 1.0
CTX = NULL
MODIFY=circuit1/6

After accumulating all the digits, it sends a NOTIFY command to the
MGC:

TRANS 12345681 MG1.network.com:12354 MEGACOP 1.0
CTX = NULL
NOTIFY=circuit1/6
OE= {called party digits}

RESPONSE will be sent back to MG as:

ACPT 12345681 MGC1.network.com:12354 MEGACOP 1.0
CTX = NULL
NOTIFY=circuit1/6

After receiving this response, the MGC instructs the incoming



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Residential MG to add the specified termination to context using ADD
command as:

TRANS 12345682 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=circuit1/6
LS={m=recvonly}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.100.89
m=audio ANY RTP/AVP 0
}

In the response of the above ADD command, MG will give the session
description of the local termination as well as the contextID.

ACPT 12345682 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
ADD=circuit1/6
ADD= RTP/177
LT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}

Then the MGC requests the outgoing R2 gateway to choose any of the
outgoing trunk, and add that termination to context using ADD command
as:

TRANS 12345683 MGC1.network.com:12354 MEGACOP 1.0
CTX = -1
ADD=Trunkgroup-1/$
LS={m=sendrecv}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.200.89
m=audio ANY RTP/AVP 0
}
RT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}

For the above ADD command, RESPONSE is sent back by R2 MG as:

ACPT 12345683 MG1.network.com: 12354 MEGACOP 1.0
CTX = C1r



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ADD=Trunkgroup-1/5
ADD= RTP/1177
LT= {v=0
c=IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}

After getting this response, a MODIFY command is sent from the MGC to
the outgoing R2 gateway to signal "seizure" on the chosen outgoing R2
trunk. MG is also requested to notify immediately as soon as "seizure
ACK" is observed at the termination.

TRANS 12345684 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
MODIFY=Trunkgroup-1/5
ED= {R2/sa}
SD= {R2/sz}

RESPONSE to the above MODIFY command will be sent by MG as:

ACPT 12345684 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
MODIFY=Trunkgroup-1/5

After having received the notification of "seizure ACK", the MGC
requests MG to send the calling and the called party digits on the
outgoing trunk. The digits are sent from MG using compelled sequence
generated by the script running in the MG. Since MG receives any of
the B group frequencies either representing the congestion condition
or the line-free condition, the associated event list contains all
the relevant events.

TRANS 12345685 MGC1.network.com:12354 MEGACOP 1.0
CTX = C1r
MODIFY= Trunkgroup-1/5
SD= {si,di}
ED={soo,un,slb,slf}

For the above MODIFY command RESPONSE is sent by R2 MG as:

ACPT 12345685 MG1.network.com:12354 MEGACOP 1.0
CTX = C1r
MODIFY=Trunkgroup-1/5


When either of the events mentioned in the event list in the MODIFY
command is observed, MG sends a notification to the MGC. Here it is
assumed that the "slf" event is observed.





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TRANS 12345686 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5
OE= {R2/slf}

RESPONSE will be sent by the MGC for this NOTIFY command as:

ACPT 12345686 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5

When the MGC gets NOTIFY command, it instructs the incoming MG to
generate a "ringback tone" to the calling user. It also passes
information about the SDP descriptor of the remote termination.

TRANS 12345687 MGC1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=circuit1/6
SD={G/rt}
RT= {v=0
c=IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}

The following response comes at the MGC.

ACPT 12345687 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=circuit1/6

Now, the MGC instructs the outgoing R2 MG to check for the "answer"
event coming on the outgoing trunk.

TRANS 12345688 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
MODIFY=Trunkgroup-1/5
ED= {T/as, EM ED:clr}

MG will send RESPONSE as follows

ACPT 12345688 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
MODIFY=Trunkgroup-1/5

When the called party answers and the "answer" is observed by the R2
MG, it notifies the MGC as:







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TRANS 12345689 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5
OE= {T/as}


RESPONSE will be sent by MGC as follows

ACPT 12345689 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5

After having received the notify message for "Answer" the mode of the
incoming MG will be set to "sendrecv".

TRANS 12345690 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
Modify = circuit1/6
LS={sendrecv}

MG will send RESPONSE as follows

ACPT 12345690 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1
Modify = circuit1/6

Then Media transfer takes place between the two until any of the user
goes on hook. It is assumed that the called party goes "onhook" and
the outgoing MG gets the "clear" signal.

TRANS 12345691 MG1.network.com:12354 MEGACOP 1.0
CTX =C1
NOTIFY=Trunkgroup-1/5
OE= {T/clr}

RESPONSE will be sent by MGC as follows

ACPT 12345691 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5

The two RTP terminations are then subtracted from the context by
respective MGs on the command of the MGC as:

TRANS 12345692 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
SUBTRACT=Trunkgroup-1/5

MG will send RESPONSE as follows




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ACPT 12345692 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
SUBTRACT=Trunkgroup-1/5

At the incoming end also, the corresponding termination is subtracted
on the command of the MGC.

TRANS 12345693 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1
SUBTRACT=circuit1/6

MG will send RESPONSE as follows

ACPT 12345693 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1
SUBTRACT=circuit1/6

Both Gateways at this point are ready for the next call.


2.3 Incoming R2Gateway and Outgoing H.323 terminal under single MGC.

---------------------------------------------------------------------
      R2  |    MG     |          MGC     |    H.323 | USER
          |           |                  |          |
---------------------------------------------------------------------
          |           |Modify(T1)EL:sz    |         |
          |     <----------               |         |
          |           |                   |         |
          |    Resp(ok)------------>      |         |
          |           |                   |         |
Seizure   |    Notify(sz)--------->       |         |
          |           |                   |         |
          |    <---------Resp(ok)         |         |
          |           |                   |         |
          |     <------------Modify(T1)   |         |
          |        SL:sa EL:di,si,sc,clr  |         |
          |           |                   |         |
          |  Resp(ok)--------->           |         |
     <----------Seizureack                |         |
          |           |                   |         |
Script will|          |                   |         |
Collect Digits|       |                   |         |
          |           |                   |         |
     <--------A6      |                   |         |
          |           |                   |         |
          | Notify(di,si,sc)-------->     |         |
          |           |                   |         |
          |    <------------Resp(ok)      |         |



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          |           |                   |         |
          |    <-----------Add(t1)        |         |
          |           |                   |         |
          |Resp(ok)------------>          |         |
          |          |                    |         |
          |          |              setup+faststart |
          |          |                ---------->   |
          |          |                    |     ring--->
          |          |                    |         |
          |          |                <-----ALERTING|
          |          |                    |         |
          |  <--------------Modify(T1)    |         |
          |            SL:G/rt            |         |
          |          |                    |         |
          |    Resp(ok)------------->     |         |
          |          |                    |         |
          |          |                    |       Off-hook
          |          |                    |    <----------
          |          |                    |         |
          |          |               <-------CONNECT+faststart
          |          |                    |         |
          |    <-------------Modify(T1)   |         |
          |         mode=sendrecv,RD      |         |
          |   Resp(ok)---------->         |         |
          |          |                    |         |
     ________________________________________________________________
                MEDIA
     ________________________________________________________________
          |          |                    |          Onhook
          |          |                    |    <----------
          |          |                    |         |
          |          |             <----------End Session
          |          |                    |         |
          |          |        End Session----------->
          |          |                    |         |
          |          |           <---------Rel-Complete|
          |          |                    |         |
          |  <-------------Subtract(T1)   |         |
          |             SL:clr            |         |
          |          |                    |         |
          |          |                    |         |
          |          |                    |         |
          |Resp(ok)-------->              |         |
          |          |                    |         |
_____________________________________________________________________

The MODIFY command is first sent by the MGC to the R2 Gateway. The
request will consist of the following lines.







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TRANS 12345678 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/*
ED= {R2/sz}

The above text indicates that MG is requested to check for seizure
signal on any of the incoming R2 termination "Trunkgroup-1/*". Since
the termination is out of context the CTX value is set to NULL. The
response from MG would be of following form

ACPT 12345678 MG1.network.com: 12354 MEGACOP 1.0
CTX= NULL
MODIFY=Trunkgroup-1/*

After having noticed seizure on a particular termination, MG will
send a NOTIFY command to the MGC:

TRANS 12345679 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6
OE= {R2/sz}

The following RESPONSE will be sent back to MG:

ACPT 12345679 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6

After having noticed the incoming seizure, the MGC will send a MODIFY
command to send a seizure acknowledgement and to collect called and
calling party digits by passing the Digit map and also requests for
calling party category. To check for the originating user going
"onhook", an event "clear" is also included in the event list:

TRANS 12345680 MGC1.network.com:12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/6
ED= {R2/di
R2/si, R2/sc, R2/clr}
SD= {R2/sa}

MG after having received the above MODIFY command sends response to
the MGC as:

ACPT 12345680 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/6

After sending seizure acknowledgement, MG invokes a script to do




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compelled sequence for the collection of calling and called party
digits according to the digit map. After accumulating all the digits,
it sends a NOTIFY command to the MGC:

TRANS 12345681 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6
OE= {di, si, sc}

RESPONSE will be sent back to MG as:

ACPT 12345681 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6

After receiving this response, the MGC instructs the incoming R2 MG
to add the specified termination to context using ADD command as:

TRANS 12345682 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=Trunkgroup-1/6
LS={m=recvonly}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.100.89
m=audio ANY RTP/AVP 0
}

In the response of the above ADD command, MG will give the session
description of the local termination as well as the contextID.

ACPT 12345682 MG1.network.com: 12354 MEGACOP 1.0
CTX = C1
ADD=Trunkgroup-1/6
ADD= RTP/177
LT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}

MGC having seized the incoming R2 trunk, proceeds with call routing.
Using local databases, it determines that the dialled digits
correspond to a H.323 entity. It will set up a TCP-IP connection and
send a H.225/Q.931  "set-up" message to the H.323 entity. In this
message, the "faststart" element carries a set of open logical
channel proposals, derived from the SDP description received from the
calling gateway:




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After receiving the set-up message the H.323 terminal sends an
ALERTING message to the calling party. On reception of this message
the MGC will send a modify that instructs the R2 gateway to generate
a "ringback" tone:

TRANS 12345683 MGC1.network.com: 12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6
SD= {G/rt}
MG sends back response as

ACPT 12345683 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
NOTIFY=Trunkgroup-1/6
When the called user accepts the call, the H.323 entity sends a
H.225/Q.931 CONNECT message to the MGC. IF the H.323 entity accepted
the faststart procedure, the faststart parameter will contain the
confirmation of the open logical channel creations in the two
directions of communication:

The MGC will send a modification request to the R2 Gateway, in order
to establish a full duplex connection and also provides the remote
descriptor.
TRANS 12345684 MGC1.network.com: 12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6
LS= {m=sendrecv}
RT= {v=0
c=IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}
The following response comes at the MGC.

ACPT 12345684 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6
At this point, the connection is established. In our example, the
call is terminated when the called party hangs up. This triggers the
End Session message from H.323 entity to the MGC. In response to this
the MGC replies with an End Session message to H.323 entity. H.323
entity finally sends a REL-COMPLETE message.

This triggers the MGC to send the SUBTRACT message to the calling R2
Gateway to disconnect the call.

TRANS 12345685 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1




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SUBTRACT=Trunkgroup-1/5
SD= {R2/clr}

MG will send RESPONSE as follows

ACPT 12345685 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1
SUBTRACT=Trunkgroup-1/5

Both ends at this point are ready for the next call.

2.4 Incoming H.323 terminal and Outgoing R2 Gateway under single MGC.

---------------------------------------------------------------------
    H.323 |     MGC            |        R2MG   |          R2
          |                    |               |
---------------------------------------------------------------------
Offhook   |                    |               |
    Setup+faststart            |               |
    ----------->               |               |
          |                    |               |
    <----------Call-Proc       |               |
          |                    |               |
          |               Add(T2)------>       |
          |                    |               |
          |              <------Resp(ok)       |
          |                    |               |
          |        Modify(T2)------>           |
          |       SL:sz ED:sa  |               |
          |            <--------Resp(ok)       |
          |                    |               |Seizure---->
          |                    |               |Seizureack<--
          |                    |               |
          |                    |               |
          |          <----------Notify(T2)     |
          |                      OE: sa        |
          |                    |               |
          |        Resp(ok)------------->      |
          |                    |               |
          |        Modify(T2)-------->         |
          |           SD: si,di|               |
          |        EL: soo,un,slb,slf,         |
          |            <-------Resp(ok)        |
          |                    |               |Compelled digits
          |                    |               |  sent
          |               <---------Notify     |
          |                    |   (slf)       |
          |               Resp(ok)----->       |




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          |                    |               |
    <--------Alerting          |               |
Ringbacktone|                  |               |
          |    Modify(T2)------------>         |
          |    EL: {T/as(EM:clr)}              |
          |                    |               |
          |           <-----------Resp(ok)     |
          |                    |               |  Answer
          |            <----------Notify(T2)   |
          |                    |    (Answer)   |
          |                    |               |
          |            Resp(ok)---------->     |
    <---------Connect+faststart|               |
          |                    |               |
     ________________________________________________________________
                MEDIA
     ________________________________________________________________
          |                    |               |      Clearback
          |        <-------------Notify clr    |
          |                    |               |
          |       Resp(ok)------------>        |
          |                    |               |
   <-------------End session   |               |
          |                    |               |
    ----------->End session    |               |
          |            subtract(T2)------->    |
    <---------REL-Complete     |               |
          |                    |               |
          |            <-----------Resp(ok)    |
          |                    |               |
_____________________________________________________________________


When the user initiates the call, the H.323 entity will establish a
TCP/IP connection with the MGC. Once the TCP/IP connection is
established, the H.323 entity sends a Q.931/H.225 set-up message to
the MGC. The message, in its user-to-user parameter, includes a "fast
start" parameter that lists a set of OpenLogicalchannel parameters.

Upon reception of the set-up message, the MGC will perform called
routing functions and determine the endpoint that corresponds the
called party number.

Then the MGC requests the outgoing R2 gateway to choose and add any
of the outgoing trunks to context using ADD command as:






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TRANS 12345680 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=Trunkgroup-1/$
LS={m=sendrecv}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.200.89
m=audio ANY RTP/AVP 0
}
RT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}

In the above command the SDP announcement is obtained by translating
the fast-start parameters. For the above ADD command, RESPONSE is
sent back by R2 MG as:


ACPT 12345680 MG1.network.com: 12354 MEGACOP 1.0
CTX = C1
ADD=Trunkgroup-1/5
ADD= RTP/1177
LT= {v=0
c=IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}

After getting this response, a MODIFY command is sent from the MGC to
the outgoing R2 gateway to signal "seizure" on the chosen outgoing R2
trunk. MG is also requested to notify immediately as soon as "seizure
ACK" is observed at the termination.

TRANS 12345681 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1
MODIFY=Trunkgroup-1/5
ED= {R2/sa}
SD= {R2/sz}

RESPONSE to the above MODIFY command will be sent by MG as:

ACPT 12345681 MG1.network.com:12354 MEGACOP 1.0
CTX =C1
MODIFY=Trunkgroup-1/5







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After having received the notification of "seizure ACK", the MGC
requests MG to send the calling and the called party digits on the
outgoing trunk. The digits are sent from MG using compelled sequence
generated by the script running in the MG. Since MG can receive any
of the group B frequencies representing either the congestion
condition or the line-free condition, the associated event list
contains all the relevant events.

TRANS 12345682 MGC1.network.com: 12354 MEGACOP 1.0
CTX = C1
MODIFY= Trunkgroup-1/5
SD= {si,di}
ED={soo,un,slb,slf}

For the above MODIFY command RESPONSE is sent by R2 MG as:

ACPT 12345682 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/5


When any of the events mentioned in the event list in the MODIFY
command is observed, MG sends a notification to the MGC. Here it is
assumed that the "slf" event is observed.

TRANS 12345683 MG1.network.com:12354 MEGACOP 1.0
CTX =C1
NOTIFY=Trunkgroup-1/5
OE= {R2/slf}

RESPONSE will be sent by the MGC for this NOTIFY command as:

ACPT 12345683 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1
NOTIFY=Trunkgroup-1/5

Now the MGC sends an ALERTING message to the calling H.323 entity
that it is assumed will generate ringing tones for the calling user.
Now, the MGC instructs the outgoing R2 MG to check for the "answer"
event coming on the outgoing trunk. This event request also embeddes
the "clear" signal
TRANS 12345684 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1
MODIFY=Trunkgroup-1/5
ED= {T/as, EM: ED clr}

MG will send RESPONSE as follows





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ACPT 12345684 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1
MODIFY=Trunkgroup-1/5

When the called party answers and the "answer" is observed by the R2
MG, it notifies the MGC as:

TRANS 12345685 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1
NOTIFY=Trunkgroup-1/5
OE= {T/as}


RESPONSE will be sent by MGC as follows

ACPT 12345685 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1
NOTIFY=Trunkgroup-1/5

In response to this the MGC, will send a "connect + faststart"
message to the H.323 entity. Then Media transfer takes place between
the two until any of the user goes on hook. It is assumed that the
called party goes "onhook" and the outgoing MG gets the "clear"
signal.

TRANS 12345686 MG1.network.com:12354 MEGACOP 1.0
CTX =C1
NOTIFY=Trunkgroup-1/5
OE= {R2/clr}

RESPONSE will be sent to MG as follows

ACPT 12345686 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1
NOTIFY=Trunkgroup-1/5

Upon reception of this notification the MGC sends an End session
message to the calling H.323 entity. And finally it sends a Rel-
complete to the calling party. In parallel the MGC sends a "subtract"
to the outgoing R2 MG.

TRANS 12345687 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1
SUBTRACT=Trunkgroup-1/5

MG will send RESPONSE as follows





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ACPT 12345687 MG1.network.com:12354 MEGACOP 1.0
CTX =C1
SUBTRACT=Trunkgroup-1/5

Now both the ends are ready for further calls.

2.5 Call flows with 2 MGCs.

For the following call scenarios where there is interaction
between two MGCs, it is assumed that the H.323 protocol is used for
MGC-MGC communication. Here it is also assumed that the number plan
for collecting the calling party number is same as that of the called
party.

2.5.1 Incoming R2GW Outgoing Residential Gateway under different MGC.

---------------------------------------------------------------------
 R2   |          MG  |     MGC    |      MGC     |    R2MG   | R2
      |              |            |              |           |
---------------------------------------------------------------------
      |              |Modify(T1) EL:sz           |           |
      |        <----------        |              |           |
      |              |            |              |           |
      |    Resp(ok)------------>  |              |           |
      |              |            |              |           |
Seizure      Notify(SZ)---------> |              |           |
      |              |            |              |           |
      |        <---------Resp(ok) |              |           |
      |              |            |              |           |
      |        <------------Modify(T1)           |           |
      |            SL:sa EL:di,si,sc,clr         |           |
      |              |            |              |           |
      |   Resp(ok)------------>   |              |           |
    <----------Seizureack         |              |           |
      |              |            |              |           |
     Script will     |            |              |           |
    Collect Digits   |            |              |           |
      |              |            |              |           |
    <----------A6    |            |              |           |
      |              |            |              |           |
      |    Notify(di,si,sc)-------->             |           |
      |              |            |              |           |
      |        <------------Resp(ok)             |           |
      |              |            |              |           |
      |        <-----------Add(t1)|              |           |
      |              |            |              |           |
      |    Resp(ok)------------>  |              |           |
      |              |        ------->Setup+     |           |
      |              |            |   Faststart  |           |






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      |              |        <-------Call-Proc  |           |
      |              |            |              |           |
      |              |            |   Add(T2)------->        |
      |              |            |              |           |
      |              |            |    <--------Resp(ok)     |
      |              |            |              |           |
      |              |            |Modify(T2)-------->       |
      |              |            |  SL:sz ED:sa             |
      |              |            |              |           |
      |              |            |   <----------Resp(ok)    |
      |              |            |              |   Seizure---->
      |              |            |              |   Seizureack<--
      |              |            |              |           |
      |              |            |              |           |
      |              |            |    <------Notify(T2)     |
      |              |            |        OE:sa             |
      |              |            |              |           |
      |              |            |    Resp(ok)----->        |
      |              |            |              |           |
      |              |            |  Modify(T2)---->         |
      |              |            |  SD: si,di               |
      |              |            |  EL: soo,un,slb,slf,     |
      |              |            |  <-----Resp(ok)          |
      |              |            |              |           |
      |              |            |              |   Compelled digits
      |              |            |              |    sent   |
      |              |            |    <--------- Notify     |
      |              |            |              |(slf)      |
      |              |            |              |           |
      |              |            |    Resp(ok)-------->     |
      |              |            |              |           |
      |              |        <--------Alerting  |           |
      |        <-------Modify(T1  |              |           |
      |              | SD:{G/rt}  |              |           |
      |              |            |              |           |
      |    Resp(ok)-------->      |              |           |
      |              |            |              |           |
      |              |            |   Modify(T2)---->        |
      |              |            |   EL: T/as   |           |
      |              |            |   (EM   :clr)            |
      |              |            |              |           |
      |              |            |        <------Resp(ok)   |
      |              |            |              |             Answer
      |              |            |        <-------Notify(T2)|







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      |              |            |               OE:(Answer)|
      |              |            |              |           |
      |              |            |    Resp(ok)-------->     |
      |              |    <-----Connect+faststart|           |
      |              |            |              |           |
      |              |            |              |           |
      |      <----------Modify(T1)|              |           |
      |              | mode=sendrecv,RD          |           |
      |              | SD:{T/as}  |              |           |
      |      Resp(ok)---------->  |              |           |
      |              |            |              |           |
      |              |            |              |           |
     ________________________________________________________________
                MEDIA
     ________________________________________________________________
      |              |            |              |           | Clearback
      |              |            |         <------Notify clr|
      |              |            |              |           |
      |              |            |       Resp(ok)-->        |
      |              |            |              |           |
      |              |    <-----End session      |           |
      |              |            |              |           |
      |              |  ----------->End session  |           |
      |              |            |  subtract(T2)---->       |
      |              |    <---------REL-Complete |           |
      |              |            |              |           |
      |     <--------Subtract(T1) |              |           |
      |        -------->Resp(ok)  |        <--------Resp(ok) |
      |              |            |              |           |
_____________________________________________________________________

The figure above depicts the call flow describing call connection
between an incoming R2 Gateway and an Outgoing R2 Gateway. During the
exchanges, MEGACOP is used by each MGC (Media Gateway Controller) to
control the respective endpoints located on the two Media Gateways.
The first command is the MODIFY command sent by the MGC to the
incoming R2 Gateway. The request will consist of the following lines.



TRANS 12345678 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/*
ED= {R2/sz}

The above text indicates that MG is requested to check for seizure
signal on the incoming R2 terminations "Trunkgroup-1/*". Since the
terminations are out of context the CTX value is set to NULL. The


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response from MG would be of following form


ACPT 12345678 MG1.network.com: 12354 MEGACOP 1.0
CTX= NULL
MODIFY=Trunkgroup-1/*


After having noticed seizure on a particular termination, MG will
send a NOTIFY command to the MGC:

TRANS 12345679 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6
OE= {R2/sz}

The following RESPONSE will be sent back to MG:

ACPT 12345679 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6

After having noticed the incoming seizure, the MGC sends a MODIFY
command to send a seizure acknowledgement and to collect called and
calling party digits by passing the Digit map and also requests for
calling party category. To check for the originating user going
"onhook", an event "clear" is also included in the event list:

TRANS 12345680 MGC1.network.com:12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/6
ED= {R2/di,
R2/si, R2/sc, R2/clr}
SD= {R2/sa}

MG after having received the above MODIFY command sends response to
the MGC as:

ACPT 12345680 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/6

After sending seizure acknowledgement, MG invokes a script to do
compelled sequence for the collection of calling and called party
digits according to the digit map. After accumulating all the digits,
it sends a NOTIFY command to the MGC:

TRANS 12345681 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL



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NOTIFY=Trunkgroup-1/6
OE= {di, si, sc}

RESPONSE will be sent back to MG as:


ACPT 12345681 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6

After receiving this response, the MGC instructs the incoming R2 MG
to add the specified termination to context using ADD command as:

TRANS 12345682 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=Trunkgroup-1/6
LS={m=recvonly}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.100.89
m=audio ANY RTP/AVP 0
}

In the response of the above ADD command, MG will give the session
description of the local termination as well as the contextID.

ACPT 12345682 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
ADD=Trunkgroup-1/6
ADD= RTP/177
LT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}

At this stage the MGC of the incoming R2 gateway sends a "set-up"
message to the second MGC. The second MGC replies with the "Callproc"
message.  The second MGC using local databases determines that the
called party number contained in the set-up message corresponds to an
R2 termination. After having recognised the called number it sends an
Add command to the outgoing MG.

TRANS 12345683 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=Trunkgroup-1/$







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LS={m=sendrecv}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.200.89
m=audio ANY RTP/AVP 0
}
RT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}
In the above command the SDP announcement is obtained by translating
the fast-start parameters. For the above ADD command, RESPONSE is
sent back by R2 MG as:

ACPT 12345683 MG1.network.com: 12354 MEGACOP 1.0
CTX = C1r
ADD=Trunkgroup-1/5
ADD= RTP/1177
LT= {v=0
c=IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}

After getting this response, a MODIFY command is sent from the MGC to
the outgoing R2 gateway to signal "seizure" on the chosen outgoing R2
trunk. MG is also requested to notify immediately as soon as "seizure
ACK" is observed at the termination.

TRANS 12345684 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
MODIFY=Trunkgroup-1/5
SD= {R2/sz}
ED:{R2/sa}
RESPONSE to the above MODIFY command will be sent by MG as:

ACPT 12345684 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
MODIFY=Trunkgroup-1/5

After having received the notification of "seizure ACK", the MGC
requests MG to send the calling and the called party digits on the
outgoing trunk. The digits are sent from MG using compelled sequence
generated by the script running in the MG. Since MG receives any of
the B group frequencies either representing the congestion condition
or the line-free condition, the associated event list contains all
the relevant events.






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TRANS 12345685 MGC1.network.com:12354 MEGACOP 1.0
CTX = C1r
MODIFY= Trunkgroup-1/5
SD= {si, di}
ED={soo,un,slb,slf}

For the above MODIFY command RESPONSE is sent by R2 MG as:

ACPT 12345685 MG1.network.com:12354 MEGACOP 1.0
CTX = C1r
MODIFY=Trunkgroup-1/5


When any of the events mentioned in the event list in the MODIFY
command is observed, MG sends a notification to the MGC. Here it is
assumed that the "slf" event is observed.

TRANS 12345686 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5
OE= {R2/slf}

RESPONSE will be sent by the MGC for this NOTIFY command as:

ACPT 12345686 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgoup-1/5

Now the MGC sends an ALERTING message to the calling the MGC, which
it is assumed, will generate "ringback" tone for the calling MG. Now,
the MGC instructs the outgoing R2 MG to check for the "answer" event
coming on the outgoing trunk.

TRANS 12345687 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1r
MODIFY=Trunkgroup-1/5
ED= {T/as, EM ED:clr}

MG will send RESPONSE as follows

ACPT 12345687 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1r
MODIFY=Trunkgroup-1/5

When the called party answers and the "answer" is observed by the R2
MG, it notifies the MGC as:

TRANS 12345688 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1r



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NOTIFY=Trunkgroup-1/5
OE= {T/as}

RESPONSE will be sent by MGC as follows

ACPT 12345688 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5

In response to this the MGC will send a "connect + faststart" message
to the calling MGC. At this point the incoming MGC sends a Modify
message to the incoming R2 MG to change the mode to "sendrecv". The
MGC also sends the remote descriptor obtained from the faststart
element of the CONNECT message. The accompanied "answer" signal
removes the "ringback" tone.

TRANS 12345689 MGC1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6
LS= {m=sendrecv}
SD={T/as}
RT= { v=0
c= IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}
The following response comes at the MGC.

ACPT 12345689 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6

At this point, the connection is established. Then Media transfer
takes place between the two until any of the user goes on hook. It is
assumed that the called party goes "onhook" and the outgoing MG gets
the "clear" signal.

TRANS 12345690 MG1.network.com:12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5
OE= {R2/clr}

MGC will send RESPONSE as follows:
ACPT 12345690 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1r
NOTIFY=Trunkgroup-1/5

Upon reception of this notification second MGC sends an End session
message to the calling MGC. And finally it sends a Rel-complete to




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the calling MGC. In parallel second MGC sends a "subtract" to the
outgoing R2 MG.

TRANS 12345691 MGC1.network.com: 12354 MEGACOP 1.0
CTX =C1r
SUBTRACT=Trunkgroup-1/5

MG will send RESPONSE as follows

ACPT 12345691 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1r
SUBTRACT=Trunkgroup-1/5
Similarly at the incoming end the first MGC, commands MG to subtract
the terminations from context at the incoming R2GW end. Once the
terminations are subtracted from context, both the ends are ready for
further calls.

2.5.2 Incoming R2 GW and outgoing SS7 GW, under different MGC.

---------------------------------------------------------------------
    R2|          MG |     MGC      |      MGC      |    MG  |SG
      |             |              |               |        |
---------------------------------------------------------------------
      |             |Modify(T1) EL:sz|             |        |
      |        <----------         |               |        |
      |             |              |               |        |
      |    Resp(ok)------------>   |               |        |
      |             |              |               |        |
Seizure     Notify(sz)--------->   |               |        |
      |             |              |               |        |
      |        <---------Resp(ok)  |               |        |
      |             |              |               |        |
      |        <------------Modify(T1)             |        |
      |            SL:sa EL:di,si,sc,clr           |        |
      |             |              |               |        |
      |   Resp(ok)----------->     |               |        |
    <----------Seizureack          |               |        |
      |             |              |               |        |
     Script will    |              |               |        |
    Collect Digits  |              |               |        |
      |             |              |               |        |
    <----------A6   |              |               |        |
      |             |              |               |        |
      |Notify(di,si,sc)-------->   |               |        |
      |             |              |               |        |
      |  <------------Resp(ok)     |               |        |






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      |             |              |               |        |
      |        <-----------Add(T1) |               |        |
      |             |              |               |        |
      |Resp(ok)------------>       |               |        |
      |             |      ------->Setup+          |        |
      |             |              |Faststart      |        |
      |             |        <-------Call-Proc     |        |
      |             |              |               |        |
      |             |              |       Add(T2)------->  |
      |             |              |               |        |
      |             |              |    <--------Resp(ok)   |
      |             |              |               |        |
      |             |              |       ------------------->IAM
      |             |              |               |        |
      |             |              |               |        |
      |             |              |         <-----------------ACM
      |             |              |               |        |
      |             |        <--------Alerting     |        |
      |        <------Modify(T1)   |               |        |
      |             | SD:{G/rt}|   |               |        |
      |             |              |               |        |
      |    Resp(ok)-------->       |               |        |
      |             |              |               |        |
      |             |              |          <-----------------ANM
      |             |       <-----Connect+faststart|        |
      |             |              |               |        |
      |             |              |               |        |
      |     <----------Modify(T1)  |               |        |
      |             |mode=sendrecv,RD|             |        |
      |             |SD: {T/as}    |               |        |
      |      Resp(ok)---------->   |               |        |
      |             |              |               |        |
      |             |              |               |        |
     ________________________________________________________________
                MEDIA
     ________________________________________________________________
      |             |              |         <-----------------REL
      |             |              |               |        |
      |             |          <-----End session   |        |
      |             |              |               |        |
      |             |    ----------->End session   |        |
      |             |              |  subtract(T2)---->     |
      |             |    <--------- REL-Complete   |        |
      |             |              |               |        |
      |   <--------Subtract(T1)    |               |        |
      |        -------->Resp(ok)   |       <--------Resp(ok)|
      |             |              |               |        |
____________________________________________________________________

The figure above depicts the call flow describing call connection
between an incoming R2 Gateway and an outgoing SS7 signalling system.
During the exchanges, MEGACOP is used by each MGC (Media Gateway



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Controller) to control the respective endpoints located on the two
Media Gateways. The first command is the MODIFY command sent by the
MGC to the incoming R2 Gateway. The request will consist of the
following lines.

TRANS 12345678 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/*
ED= {R2/sz}

The above text indicates that MG is requested to check for seizure
signal on any of the incoming R2 termination "Trunkgroup-1/*". Since
the terminations are out of context the CTX value is set to NULL. The
response from MG would be of following form

ACPT 12345678 MG1.network.com: 12354 MEGACOP 1.0
CTX= NULL
MODIFY=Trunkgroup-1/*


After having noticed seizure on the specified termination, MG will
send a NOTIFY command to the MGC:

TRANS 12345679 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6
OE= {R2/sz}

The following RESPONSE will be sent back to MG:

ACPT 12345679 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6

After having noticed the incoming seizure, the MGC will send a MODIFY
command to send a seizure acknowledgement and to collect called and
calling party digits by passing the Digit map and also requests for
calling party category. To check for the originating user going
"onhook", an event "clear" is also included in the event list:

TRANS 12345680 MGC1.network.com:12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/6
ED= {R2/di,
R2/si, R2/sc, R2/clr}
SD= {R2/sa}

MG after having received the above MODIFY command sends response to
the MGC as:



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ACPT 12345680 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
MODIFY=Trunkgroup-1/6

After sending seizure acknowledgement, MG invokes a script to do
compelled sequence for the collection of calling and called party
digits according to the digit map. After accumulating all the digits,
it sends a NOTIFY command to the MGC:

TRANS 12345681 MG1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6
OE= {di, si, sc}

RESPONSE will be sent back to MG as:

ACPT 12345681 MGC1.network.com: 12354 MEGACOP 1.0
CTX = NULL
NOTIFY=Trunkgroup-1/6

After receiving this response, the MGC instructs the incoming R2 MG
to add the specified termination to context using ADD command as:

TRANS 12345682 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=Trunkgroup-1/6
LS={m=recvonly}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.100.89
m=audio ANY RTP/AVP 0
}

In the response of the above ADD command, MG will give the session
description of the local termination as well as the contextID.

ACPT 12345682 MG1.network.com: 12354 MEGACOP 1.0
CTX = C1
ADD=Trunkgroup-1/6
ADD= RTP/177
LT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}


At this stage the MGC of the incoming R2 gateway sends a "set-up"
message to the second MGC. The second MGC replies with the "Callproc"
message.  The second MGC using local databases determines that the



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called party number contained in the set-up message corresponds to an
SS7 termination. After having recognised the called number it sends
an Add command to the outgoing MG.

TRANS 12345683 MGC1.network.com: 12354 MEGACOP 1.0
CTX = -1
ADD=Trunkgroup-1/$
LS={m=sendrecv}
ADD= RTP/ANY
LS= {m=sendrecv}
LT= {v=0
c=IN IP4 100.100.200.89
m=audio ANY RTP/AVP 0
}
RT= {v=0
c=IN IP4 100.100.100.89
m=audio 4321 RTP/AVP 0
}

In the above command the SDP announcement is obtained by translating
the fast-start parameters. For the above ADD command, RESPONSE is
sent back by R2 MG as:

ACPT 12345683 MG1.network.com: 12354 MEGACOP 1.0
CTX = C1r
ADD=Trunkgroup-1/5
ADD= RTP/1177
LT= {v=0
c=IN IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}

After getting this response, an IAM message is sent from the MGC to
the outgoing Signalling gateway to send "IAM" on the chosen outgoing
SS7 trunk. As soon as an ACM message is received on the signalling
Gateway, the second MGC is informed about it. Now the called MGC
sends an ALERTING message to the calling MGC that  assumes will
generate "ringback" tone for the calling MG.


When the called party answers and the "ANM" is observed by the SG on
the SS7 trunk, it is passed to the called MGC. In response to this,
called MGC will send a "connect + faststart" message to the calling
MGC. At this point, the incoming MGC sends a Modify message to the
incoming R2MG to change the mode to "sendrecv" along with the remote
descriptor obtained from the faststart element of the CONNECT
message.

TRANS 12345684 MGC1.network.com:12354 MEGACOP 1.0
CTX = C1



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MODIFY=Trunkgroup-1/6
LS= {m=sendrecv}
SD={T/as}
RT= {v=0
c=In IP4 100.100.200.89
m=audio 4320 RTP/AVP 0
}
The following response comes at the MGC.

ACPT 12345684 MG1.network.com:12354 MEGACOP 1.0
CTX = C1
MODIFY=Trunkgroup-1/6

At this point, the connection is established. Then Media transfer
takes place between the two until any of the user goes on hook. It is
assumed that the called party goes "onhook" and the outgoing SG gets
the "RELEASE" message.
Upon reception of "RELEASE", called MGC sends an End session message
to the calling MGC. And finally it sends a Rel-complete to the
calling MGC. In parallel second MGC sends a "subtract" to the
incoming R2 MG.

TRANS 12345685 MGC1.network.com:12354 MEGACOP 1.0
CTX =C1r
SUBTRACT=Trunkgroup-1/5

MG will send RESPONSE as follows

ACPT 12345685 MG1.network.com: 12354 MEGACOP 1.0
CTX =C1r
SUBTRACT=Trunkgroup-1/5
Similarly at the first MGC also subtracts the incoming R2GW.
Now both the ends are ready for further calls.

3.0 Conclusions:

The R2 package proposed here emulates some of the essential
functionality required by MGC to do R2 signalling at both ends. For
complete emulation of R2 signalling, i.e., to get the complete
essence of R2 signalling some more events and signals in this R2
package are required to be included. For example, events for language
digit detection, echo suppresser information, type of circuit etc
have not been included.
     R2 signalling is an end-to-end register signalling system. In
the call flows shown, R2 signalling was made link by link by the
Gateway. But in future versions its possible that R2 signalling is
made end-to-end with Gateway doing MF relaying function.




Vikas,Sandip,Prashant,Madhu                                 [Page45





INTERNET-DRAFT              R2 package                May 24,1999



4.0 References:

[1] Brian Rosen, Paul Sijben, Eric Zimmerer "draft-ietf-megaco-
protocol-01.txt" , "work in progress".
[2] CCITT Specifications of signalling system R2 Recommendations
Q.400 to Q.490.
[3] ITU-T, Recommendation H.323 (02/98), ôPACKET-BASED MULTIMEDIA
COMMUNICATIONS SYSTEMS.ö


5.0 AuthorÆs address:

Vikas Bajaj
Hughes Software Systems,Ltd.
Gurgaon,Haryana,India. 122015.
Ph: (91)-11-346666.Ex-2272.
Fax: (91)-124-342810 or 811.
Email: vbajaj@hss.hns.com.

Sandhip Ranjhan
Hughes Software Systems,Ltd.
Gurgaon,Haryana,India. 122015.
Ph: (91)-11-346666.Ex-2248
Fax: (91)-124-342810 or 811.
Email: sranjhan@hss.hns.com.

Prashant Jain
Hughes Software Systems,Ltd.
Gurgaon,Haryana,India. 122015.
Email: prjain@hss.hns.com.

Madhu Babu
Hughes Software Systems,Ltd.
Gurgaon,Haryana,India. 122015.
Email: bmbabu@hss.hns.com.



Vikas,Sandip,Prashant,Madhu                                [Page46]


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