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Internet Engineering Task Force                          Fernando Cuervo
INTERNET DRAFT                                           Nortel Networks
April 16, 1999                                         Christian Huitema
Expires October 16, 1999                          Telcordia Technologies
<draft-ietf-megaco-protocol-01.txt>                          Keith Kelly
                                                                NetSpeak
                                                             Brian Rosen
                                                            FORE Systems
                                                             Paul Sijben
                                                     Lucent Technologies
                                                           Eric Zimmerer
                                                  Level 3 Communications


                            MEGACO Protocol




Status of this document

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026

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

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

To view the entire list of current Internet-Drafts, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe),
ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim),
ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).



IMPORTANT NOTE

This version of the draft has been rushed so that members of the WG not
part of the small design team that created this document could have
early input to the design process. The last few sections of the document
have not been reviewed by the team, and are largely lifted from other
documents, especially the MGCP document. The design team did not reach



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consensus on several major issues, including how the protocol messages
will be encoded. This has complicated text in several areas. The latter
sections (the un-reviewed ones) make assumptions on encoding which have
not been agreed to. The team feels that presenting the information con-
tained in these sections will assist readers to understand the proposal
in greater depth, and thus chose to leave the text as is.

Abstract

This document is an early draft of a proposed protocol that can be used
to control a Media Gateway (MG) from an external controller called a
Media Gateway Controller (MGC).

The document is organized into the following major sections:

*    The Introduction section presents a high-level overview of the pro-
     tocol.  It discusses the connection model used and provides an
     example call flow to help illustrate the protocol's functionality.

*    The Commands section presents a description of each of the opera-
     tions supported along with their parameters.

*    The Security section presents the security requirements of the pro-
     tocol and describes its usage of IP security services (IPSEC).

*    The Syntax section presents the syntactical elements of the proto-
     col independent of its encoding.

*    The Transport section presents how the protocol is carried on a
     packet network and describes the reliability and fail-over mechan-
     isms that it supports.

*    The Event Packages and Termination Classes section describes the
     elements of commonly implemented devices and services.

















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Table of Contents                                             Page

1.  Introduction ..............................................  5
   1.1.  High Level Description of the Protocol ...............  5
      1.1.1.  Connection Model ................................  5
      1.1.2.  Terminations ....................................  8
      1.1.3.  Termination Capabilities ........................  8
      1.1.4.  Instantiation of a Termination An MG realizes ...  9
      1.1.5.  Termination Dynamics ............................  9
      1.1.6.  Issuing Commands in Transactions ................ 11
      1.1.7.  Sample Command Flow ............................. 12
2.  Commands .................................................. 15
   2.1.  Names and Common Parameters .......................... 16
      2.1.1.  Context Identifiers ............................. 16
      2.1.2.  Termination Names ............................... 16
      2.1.3.  Specifying Properties ........................... 17
      2.1.4.  Termination State Properties .................... 18
      2.1.5.  Termination Descriptors ......................... 19
      2.1.6.  Events, Signals and Packages .................... 19
      2.1.7.  SignalDescriptors ............................... 20
      2.1.8.  EventDescriptors ................................ 21
      2.1.9.  Digit Maps ...................................... 21
      2.1.10.  Statistics ..................................... 23
   2.2.  Termination Management Commands ...................... 24
      2.2.1.  Add ............................................. 24
      2.2.2.  Modify .......................................... 25
      2.2.3.  Subtract ........................................ 27
      2.2.4.  Move ............................................ 28
      2.2.5.  Audit ........................................... 28
   2.3.  MG-Issued Commands ................................... 30
      2.3.1.  Notify .......................................... 30
      2.3.2.  ServiceChange ................................... 31
   2.4.  The following table lists the defined commands, and .. 33
3.  MG-MGC Control Associations ............................... 33
   3.1.  Multiple MGCs per MG ................................. 33
   3.2.  Cold Start ........................................... 34
   3.3.  Upon failure to obtain a reply, either from the ...... 35
   3.4.  Failover ............................................. 35
      3.4.1.  Failure of an MG ................................ 35
      3.4.2.  Failure of an MGC ............................... 35
   3.5.  Error Codes .......................................... 36
4.  Security Considerations ................................... 36
   4.1.  Protection of Media Connections ...................... 38
5.  Syntax .................................................... 40
   5.1.  Termination Names .................................... 44
   5.2.  Events, Signals and Packages ......................... 45
   5.3.  Digit Maps ........................................... 47
   5.4.  Statistics ........................................... 48



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   5.5.  Examples ............................................. 51
      5.5.1.  Example Add transaction: ........................ 52
      5.5.2.  Example response to Add transaction: ............ 52
      5.5.3.  Example Modify transaction: ..................... 52
      5.5.4.  Example Subtract transaction: ................... 52
   5.6.  Transaction Response Codes ........................... 53
      5.6.1.  Transaction Response Success Codes .............. 53
      5.6.2.  Transaction Response Reject Codes ............... 53
6.  Transport ................................................. 54
   6.1.  Transport capabilities, and relationship to Transport  54
7.  Event Packages and Termination Classes .................... 55
   7.1.  Basic Event Packages ................................. 56
      7.1.1.  Generic Media Event Package ..................... 56
      7.1.2.  DTMF Event Package .............................. 57
      7.1.3.  MF Event Package ................................ 60
      7.1.4.  Trunk Event Package ............................. 61
      7.1.5.  Line Event Package .............................. 62
      7.1.6.  Handset emulation Event Package ................. 66
      7.1.7.  RTP Event Package ............................... 67
      7.1.8.  Network Access Server Event Package ............. 68
      7.1.9.  Announcement Server Event Package ............... 69
      7.1.10.  Script Event Package ........................... 70
   7.2.  Basic Termination Classes ............................ 71
      7.2.1.  DS0 Terminations ................................ 71
      7.2.2.  Analog Terminations ............................. 72
      7.2.3.  RTP Audio Terminations .......................... 74
      7.2.4.  ATM audio Terminations .......................... 78
      7.2.5.  Network access service Termination .............. 80
8.  Acknowledgements .......................................... 84
9.  References ................................................ 84
10.  Authors' Addresses ....................................... 85




















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1.  Introduction

This document describes the MEGACO protocol for controlling Media Gate-
ways from external call control elements called Media Gateway Controll-
ers.

1.1.  High Level Description of the Protocol

This section describes the model and main concepts upon which the MEGACO
Protocol is built.  It is intended to familiarize the reader with the
model, terminology and working concepts of the protocol.  This section's
contents are illustrative and do not intend to supersede information
contained in later sections of this document.  Where discrepancies may
exist, the later sections shall be assumed to contain the correct infor-
mation.

1.1.1.  Connection Model

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 analog loops or timeslots on a
TDM channel, as well as more ephemeral representations of flow termina-
tions, such as RTP streams.




























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         *======================================================*
         | Media Gateway                                        |
         |          +-----------------------------------+       |
         |          | Context       +---+               |       |
         |          |               | T |               |       |
         | +---+    |               +-+-+               |       |
         | | T |    |                 |                 |       |
         | +---+    |  +---+         +-+         +---+  |       |
         |          |  | T +---------+M+---------| T |  |       |
         |          |  +---+         +-+         +---+  |       |
         |          |                 |                 |       |
         |          |               +-+-+               |       |
         |          |               | T |               |       |
         |          |               +---+               |       |
         |          +-----------------------------------+       |
         |                                                      |
         | +----------------------+      +---------------+      |
         | | Context              |      | Context       |      |
         | |  +---+         +-+   |      |  +---+    +-+ |      |
         | |  | T +---------+M+   |      |  | T +----+M+ |      |
         | |  +---+         +-+   |      |  +---+    +-+ |      |
         | |                 |    |      +---------------+      |
         | |               +-+-+  |                             |
         | |               | T |  |                             |
         | |               +---+  |                             |
         | +----------------------+                             |
         *======================================================*

             Examples of Contexts and Terminations Within an MG




Contexts represent a star configuration (i.e.-a variable number of
interconnected nodes) of Terminations of a single media type.  Audio
connections are modeled by viewing the Context as a mixing bridge (M).
For connections involving other media types and for mixed media gate-
ways, the Context's behavior will be described as an extension to the
protocol.  There are commands to Add Terminations to a Context, Subtract
Terminations from a Context, and Move Terminations between two Contexts.

A Context must have at least one Termination and a Termination may
belong to no more than one Context at a given time.  A Context is
created by the Add of its first Termination and is destroyed by a Sub-
tract of its last remaining Termination.  It is possible to move a Ter-
mination from one Context to another with the use of the Move command.
It is also possible for a Termination to exist outside of a Context.



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A Media Gateway may limit the number of Terminations that it supports in
a given Context.  For example, a limit of two might exist for very sim-
ple gateways.  A limit of three might be common for gateways that sup-
port a three-way calling but not multi-way calling of any larger propor-
tions.

To illustrate the use of a Context, consider a Media Gateway that pro-
vides media adaptation between the PSTN and a VoIP network.  In this
case a typical Context might contain two Terminations, one representing
a PSTN trunk (a DS0 Termination) and the other an RTP Stream Termina-
tion.  A PSTN hairpin connection would be represented by a Context with
two DS0 Terminations in it.  A three-way call and larger conferences
would be represented by a Context with three or more Terminations in it.

The use of Contexts to represent conferences is very powerful since it
enables a description of the conference dynamics that is not restricted
in any way by the order in which Terminations are added or subtracted.
For instance, no special operations are required when a participant in a
conference drops out.  Its Termination may be subtracted without affect-
ing the connectivity of the Terminations remaining in the conference.

The call-waiting scenario shown below illustrates the use of the Move
command to relocate a Termination between Contexts.  In this example,
Terminations T1 and T2 belong initially to Context C1.  T1 might be the
line side of a residential gateway, while T2 could represent an RTP
Stream Termination.  When T1 is connected to T2 in Context C1 a new call
arrives for T1 from Termination T3.  T3 is placed in Context C2.  After
alerting is applied to T1 in Context C1 and T1 provides signaling to
accept the waiting call, T1 is moved from C1 to C2 through use of the
Move command.  The active call is represented now by C2 and the call on
hold is represented by C1.




















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           Call Waiting Scenario:

           Initial Call
            +-C1--------------------+
            |  +---+   +-+   +---+  |
            |  |T1 +---+M+---| T2|  |
            |  +---+   +-+   +---+  |
            +-----------------------+

           New Call Arrives

            +-C1--------------------+    +-C2--------------------+
            |  +---+   +-+   +---+  |    |          +-+   +---+  |
            |  |T1 +---+M+---| T2|  |    |          +M+---| T3|  |
            |  +---+   +-+   +---+  |    |          +-+   +---+  |
            +-----------------------+    +-----------------------+

           Waiting Call Answered

            +-C1--------------------+    +-C2--------------------+
            |          +-+   +---+  |    |  +---+   +-+   +---+  |
            |          +M+---| T2|  |    |  |T1 +---+M+---| T3|  |
            |          +-+   +---+  |    |  +---+   +-+   +---+  |
            +-----------------------+    +-----------------------+




1.1.2.  Terminations

A Termination representing a physical device may be permanently instan-
tiated and can exist outside of a Context.  Terminations representing
packet flows are typically ephemeral and are created within a Context as
a byproduct of an Add command.

All Terminations, ephemeral or not, are named entities and are members
of their specific TerminationClass.  Names are hierarchical.  Termina-
tion names may be "underspecified" by the MGC and subsequently given a
unique name (i.e.-the last component of the hierarchical name will be
unique) by the Media Gateway.  Wildcards may be used in the specifica-
tion of a name.  Section [2.1.2] describes in detail the structure and
properties of entity names used in the MEGACO Protocol.

1.1.3.  Termination Capabilities

Membership in a TerminationClass determines the capabilities of a Termi-
nation. The TerminationClass defines the default values and allowable



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ranges for the Termination's capabilities.  Capabilities include:

*    Properties, such as Termination address, media parameters, security
     parameters, etc.  These are grouped into Profiles.

*    Events and Signals that a Termination supports.  These are grouped
     in Packages.

*    Statistics that are kept for Terminations of this Class

A TerminationClass is described by a list of Profiles, Packages and
statistics that it implements. TerminationClasses, Profiles and Packages
cannot be created or modified using the commands of the Megaco protocol,
but this document defines several commonly implemented ones.

The capabilities of a Termination can be obtained using the Audit com-
mand.

1.1.4.  Instantiation of a Termination An MG realizes instances of a
TerminationClass. The Terminations are instantiated for each "port" on
an MG, and are instantiated by the MG when it restarts (or potentially
by some administrative provisioning means outside the scope of the Pro-
tocol).  For Physical Terminations, all instances of a Termination are
instantiated by the MG when it restarts (or potentially by some adminis-
trative provisioning means).  Ephemeral Terminations are instantiated by
the Add command, and destroyed by the Subtract command.

The "highest order" (first component of a hierarchical name) termination
has a full set of properties that can be altered by the MGC; they
represent default values for fully instantiated Terminations.  The Pro-
file defines the initial default values assumed by the Termination upon
MG restart.

1.1.5.  Termination Dynamics

As Terminations are Added or Moved it is necessary to specify state and
media parameters for, Events to be detected on, and Signals to be
applied to such Terminations within the Context in which they exist.  It
may also be necessary during the life of a Termination within a Context
to Modify these properties.

For Terminations representing physical entities it might also be desir-
able to Modify their properties as they are Subtracted from a Context.
This may be the case if a configuration different to the one provided by
the defaults is needed.  Such Terminations may have their properties
Modified outside of their existence within a Context.

The protocol assumes that it is the MG that is responsible for creating



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the network connection to the other side of the call.  The MGC directs
that it do so by, for example, creating an RTP termination, which would
have the side effect of causing the MG to create an RTP flow to the
other party.  On an ATM network using SVCs, it is the MG that would use,
for example, UNI to create a bearer connection.

The Add, Subtract, Move and Modify commands may affect the following
sets of properties:

*    TerminationState: A list of properties that define the state of the
     Termination, but which are not directly linked to the description
     of a media flow, to an Event list or to a Signal list.

*    LocalTerminationDescriptor and RemoteTerminationDescriptor: Lists
     of properties describing the processing of the media flow in each
     direction.

*    EventsDescriptor: A list of Events that should be detected on the
     Termination.

*    SignalDescriptor: A list of Signals that should be applied on the
     Termination.


        For example, the Add Command has the following form:

                         Add(TerminationId,
                             [LocalTerminationState,]
                             [LocalTerminationDescriptor,]
                             [RemoteTerminationDescriptor,]
                             [EventsDescriptor,]
                             [SignalDescriptor])


All parameters listed are optional except for the TerminationId.  This
allows each command to specify exactly what needs to be modified.  Addi-
tionally, some parameters may not be required for certain TerminationC-
lasses.  For instance, DS0s do not use RemoteTerminationDescriptors.
These descriptors are used only for packet TerminationClasses.

A Termination is programmed to look for specific Events through the
EventsDescriptor, which is a parameter to Add, Modify and Subtract.
When a Termination detects an Event that matches the types of Events it
is programmed to detect, the MG generates a Notify command.

The MG can generate a ServiceChange message.  ServiceChange has a number
of uses: Registration of an MG with an MGC, notification of imminent
downtime for one or more Terminations, notification that one or more



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Terminations has already gone out of service, and notification that one
or more Terminations have been brought back into service.

Detailed definitions of Commands and their Responses are provided in
Section 2.

1.1.6.  Issuing Commands in Transactions

The protocol has been designed to allow multiple Commands to be packed
in single TransactionRequest.  The corresponding Responses are received
in a single Transaction reply.  There are two types of replies, a Tran-
sactionAccept and a TransactionReject.  A Transaction allows Commands to
share fate and guarantees ordered processing.  Multiple Transactions
may, in turn, be packed into a single message.

Commands in a Transaction are executed sequentially according to an "all
or nothing rule".  That is, a TransactionAccept includes successful
Responses for ALL the Commands in the corresponding TransactionRequest.
A TransactionReject is sent when one of the Commands included in the
Transaction fails.  Responses for the Commands in a TransactionReject
are issued as follows:

*    All Commands before the point of failure in the Command sequence
     should have a Response equal to "non-executed".

*    The failed Command should have a Response with a Reason Code.

*    Commands after the point of failure are not processed and, there-
     fore, Responses are not issued for them.

The parsing mechanism described in the coding section (section 3) speci-
fies how responses or reason codes are associated with individual Com-
mands.

When a MGC issues Commands to a MG, a Context must always be specified.
This is quite natural for Add and Subtract.  For Modify Commands on a
Termination that is not in a Context, the null Context must be speci-
fied, which changes the default values of properties for that Termina-
tion.  A Move Command clearly involves two Contexts, however only the
target Context needs to be specified (i.e. the Move has the semantics of
"Move-To").  Within a Transaction, all Commands that apply to a Context
must appear after the ContextId parameter.

The following lines illustrate (i.e., syntax is ad-hoc and actions some-
what simplified) the use of Transactions in the call-waiting example of
section 1.1.1.  The Transaction that creates the second Context, applies
Signals to Termination T1 (to indicate call-waiting) and detects Events
from T1 (to swap the call) is formed as follows:



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   Transaction(TransactionId=12345
               ContextId=* Add(T3)
               ContextId=C1 Modify(T1, EventDescriptor, SignalDescriptor) )


The Commands in this Transaction are processed sequentially.  First, the
MG creates a Context to Add T3.  Second, T1 is programmed to Signal the
waiting call and collect the Events that operate the call-waiting
feature.

The next Transaction shows the Commands issued by the MGC to swap the
Terminations.

   Transaction(TransactionId=12346
                   ContextId=C2 Move(T1) Modify(T3, TerminationState)
                   ContextId=C1 Modify(T2, TerminationState) )


Again, the Commands in this Transaction are processed sequentially.
First, the MG moves T1 from C1 into C2.  Then it modifies the Mode of T3
to Sendrecv. Finally, T2 in C1 is set to Receive Mode.

1.1.7.  Sample Command Flow

This section presents an illustration of the use of the protocol Com-
mands to establish a communication between two Residential Gateways over
an IP trunking network, both MGs are under the control of the same MGC.























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|Step |    User   |   ResMG     |       MGC      |   ResMGr    |    User   |
|_____|___________|_____________|________________|_____________|___________|
|    0|           |       <------CTX=null,Modify(T1)           |           |
|     |           |      Resp------------->      |             |           |
|     |           |    (Ok,ready, looking for Off-hook)        |           |
|    1| Off-hook  | Notify---------------->      |             |           |
|     |           |             |    (off-hook recorded)       |           |
|     |           |       <--------------Resp(Ok)|             |           |
|    2|Acc Digits |             |                |             |           |
|     |           |             |                |             |           |
|    3|DgtsColct'd| Notify     ----------->      |             |           |
|    4|           |       <--------------Resp(Ok)|             |           |
|     |           |             |                |             |           |
|    5|           |       <------CTX=* ADD(T1)   |             |           |
|     |           |             |       ADD(RTP/* LocalDesc)   |           |
|    6|           | CTX=C1 --------->            |             |           |
|     |           |    Resp(Ok) |                |             |           |
|     |           |    Resp(RTP/Id,LocalDesc,RemoteDesc        |           |
|     |           |             |                |             |           |
|    7|           |             |CTX=* ADD(T1r)--------->      |           |
|     |           |             |       ADD(RTPr/*,LocalDesc,RemoteDesc)   |
|     |           |             |                |             |           |
|    8|           |             |      <---------------CTX=C1r |           |
|     |           |             |                |   Resp(Ok)  |           |
|     |           |          Resp(RTP/Id,LocalDesc,RemoteDesc) |           |
|     |           |             |                |             |           |
|    9|           |             |CTX=C1r -------------->       |           |
|     |           |             |     Modify(T1r,SignalList=Ring)          |
|     |           |             |                |             |           |
|     |           |             |                |             |           |
|   10|           |             |      <---------------CTX=C1r |  Ring     |
|     |           |             |                |   Resp(Ok)  |           |
|     |           |             |                |             |           |
|   11|           |       <-------CTX=C1 Modify(T1, SignalList=Ringback)   |
|     |           |             |        Modify(RTP/Id,LocalDesc,RemoteDesc)
|   12| Ring-Back | CTX=C1 --------->            |             |           |
|     |           |    Resp(Ok) |                |             |           |
|     |           |    Resp(RTP/Id,LocalDesc,RemoteDesc)       |           |
|     |           |             |                |             |           |
|   13|           |             |    <------------- Notify     |  Off-hook |
|   14|           |             |   Resp(Ok)---------->        |           |
|     |           |             |                |             |           |
|     |           |             |                |             |           |
|   15|           |       <------CTX=C1 Modify(T1,TerminalState=Sendrcv    |
|     |           |             |                | SignalList) |           |
|   16|           | CTX=C1 --------->            |             |           |
|     |           |    Resp(Ok) |                |             |           |



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     CTX = ContextID


Step 0:
     The MGC issues a Modify Command to request that T1 detect an Off-
     hook and proceed with digit collection

Step 1:
     The Off-hook is detected, the Notify Command is issued and the
     Off-hook recorded for billing purposes.

Step 2:
     The Termination collects and accumulates digits according to an
     appropriate digit map.

Step 3:
     The collected digits are sent to the MGC in a Notify Command.

Step 4:
     The MGC acknowledges the digit string.

Step 5:
     After determining that the digit string is valid to initiate a
     call, the MGC uses the Add Command to create a Context that
     includes T1 and a yet unnamed ephemeral packet Termination (RTP/*).
     The RTP Termination receives only a LocalTerminationDescriptor that
     specifies, for instance, a choice of codecs.

Step 6:
     The reply to the Add Command includes a named Context (C1) and a
     named RTP Termination (RTP/Id) with its LocalTerminationDescriptor
     including supported Codecs and the receiving RTP port.

Step 7:
     The MGC can now instruct the remote Residential MG to Add the Ter-
     mination that corresponds to the dialed string (e.g., T1r) and a
     corresponding RTP Termination in a Context.  The information
     returned in T1's LocalTerminationDescriptor is passed to the remote
     Residential MG in the RemoteTerminationDescriptor.  The LocalTer-
     minationDescriptor specifies the Codecs for T1r.

Step 8:
     The reply to the Add Command includes a named Context (C1r) and a
     named RTP Termination (RTP/Idr) with its LocalTerminationDescriptor
     including supported Codecs and the receiving RTP port.

Step 9:
     The MGC can now request that Ringing be applied on T1r.  The Modify



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     Command is used for this.  Looking for Off-hook is simultaneously
     programmed in T1r.

Step 10:
     The Response indicating that Ringing is applied is sent to the MGC.

Step 11:
     Two Modify commands are issued in this Transaction.  The first
     requests that Ring-back be applied to T1.  The second provides the
     RemoteTerminationDescriptor, which indicates the remote RTP receiv-
     ing port.

Step 12:
     The TransactionReply acknowledges that Ringback is being applied
     and the RTP parameter settings have been updated.

Step 13:
     The remote user goes off-hook.  A Notify Command conveys that
     information to the MGC. It is assumed that the off-hook command has
     an associated action that cancels ringing.

Step 14:
     The Notify is acknowledged by the MGC.

Step 15:
     The MGC issues a Modify Command to T1 to set the two-way talk path
     and cancel ringback.

Step 16:
     The MG acknowledges that the call set up is complete.

2.  Commands

Commands from the MGC to the MG are grouped into Transactions, each of
which requires a Transaction ID.  Transactions consist of one or more
Actions.  Each Action is limited to operate within a single Context and
consequently must specify a ContextID.  There are two circumstances
where a specific ContextID is not provided.  One is the case of modifi-
cation of a Termination outside of a Context.  The other is where the
controller requests the gateway to create a new Context.  Each of these
two cases has a distinguished value for ContextID

An Action consists of a series of Commands (Add, Subtract, Modify, Move,
etc.).  These Commands have very similar parameters, which may include:

*    TerminationState: A list of properties that define the state of the
     Termination, but which are not directly linked to the description
     of a media flow, to an Event list, or to a Signal list.  This



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     includes a description of the media handling at the Termination
     (e.g., the Mode parameter that indicates loopback, COT, etc.) and a
     description of the handling of accumulated Events that are pending
     for processing (i.e., "buffered events").

*    LocalTerminationDescriptor and RemoteTerminationDescriptor: Lists
     of properties describing the processing of the media flow in each
     direction.  These are expressed in the form of SDPdescriptors[ref].

*    EventsDescriptor: A list of Events that should be detected on the
     Termination. These Events must be supported by the Package(s) of
     the TerminationClass.  The EventDescriptor can be augmented by a
     DigitMap.

*    SignalDescriptor: A list of Signals that should be applied on the
     Termination. These Signals must be supported by the Package(s) of
     the TerminationClass.

*    A DigitMapDescriptor, which creates, deletes, or redefines a Digit
     Map.  A Digit Map is a concise description of how an MG is to han-
     dle a series of events from the detection of tones (such as from
     DTMF tone detection).

Responses which return information do so in the form of a LocalTermina-
tionDescriptor, RemoteTerminationDescriptor, or a Statistics summary.

2.1.  Names and Common Parameters

2.1.1.  Context Identifiers

Contexts are identified by a ContextID, which is assigned by the Media
Gateway and is unique within the scope of the Media Gateway.  The proto-
col makes reference to two distinguished values:

*    The null Context, which is used to refer to a Termination outside
     of a Context.  When used with a Modify Command, such a reference
     changes the default values for the Termination.

*    The "unspecified" Context, which is used to request that the MG
     create a new Context.  The actual ContextID must be returned to the
     MGC for subsequent use.

2.1.2.  Termination Names

Names for Terminations (called a "TerminationID") are hierarchical.  A
separation character delimits the components of a name from one another.
An example name in a Termination Class that implements a channelized T3
is "com1/3/17".  This name refers to a T3 called "com1", the "3"



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specifies a specific DS1 in the T3.  The "17" specifies a specific DS0
in the DS1.

There is a special Termination called "Root".  Root refers to the MG
itself.

TerminationIDs in Commands may use wildcards.  Two wildcard constructs
are provided: "all" and "choose".  The "all" construct allows a Command
to specify all possible values of a component.  One can, for example,
use "all" to refer to all DS1s of a T3 (com1/*).

When an Ephemeral Termination is to be created, the TerminationID may
given with the last component specified as "choose".  The MG would
create a fully instantiated Termination and supply a unique name which
must be returned to the MGC and be used for subsequent Transactions.
The MGC may supply a unique TerminationID, in which case the MG is
obliged to use that name.  MGs MAY refuse a request to choose a name, in
which case they must return an appropriate error code

2.1.3.  Specifying Properties

Commands may include descriptors.  Each descriptor has a set of legal
properties that may be included, which is part of the definition of the
Termination Class (properties legal for TerminationState, LocalTermina-
tionDescriptor and RemoteTerminationDescriptor), or Package (properties
legal for EventDescriptor or SignalDescriptor).  In a descriptor, each
of the properties may be fully specified, under-specified, or unspeci-
fied.

*    Fully specified properties have a single, unambiguous value that
     the MGC instruct the MG to use for the specified parameter

*    Under-specified properties have a list of potential values.  The MG
     chooses one value from the offered list, and returns the value it
     chose to the MGC.  A common example is choice of codec.  The MGC
     may allow the MG to choose from G.729a, G.723 or G.711.  The MG's
     choice may be limited based on availability of DSP resources at the
     time the request was made.  The order in which the MGC presents
     choices to the MG represents the MGCs order of preference for the
     values offered, which the MG is encouraged, but not obligated to
     respect.

*    Unspecified properties (legal properties which do not occur in the
     descriptor) result in the MG retaining the previous value for that
     parameter.  Each property has a default value, which is the value
     assumed by the property when it is not part of a context, or when
     the Termination is added to a Context but not assigned a specific
     value when added.  Default values can be changed by the MGC.



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2.1.4.  Termination State Properties

TerminationState groups a list of properties that define the state of
the Termination, but are not directly linked to a media flow, to an
Event list or to a Signal list. These properties are:

*    TerminationMode

*    EventBufferProcessing

*    EventBufferNotification

The TerminationMode parameter indicates the relation between the Termi-
nation and the "star" connection of the Context. The mode are "send
only" (sendonly), "receive only" (recvonly), "send/receive" (sendrecv),
"inactive" (inactive), "outofservice" and "test" (test).

The handling of the media received on the Termination is determined by
the TerminationMode parameter value:

*    Termination whose mode is "send", or "send/receive" receive the
     signals mixed in the Context, according to media specific rules -
     audio Terminations for example, will receive the sum of the audio
     flows coming from all other Terminations, excluding those coming
     from this specific Termination.

*    The "test" mode is used during maintenance and continuity test
     operations. There are several defined Packages that implement vari-
     ous forms of tests that can be applied to a Termination.

The optional EventBufferProcessing and EventBufferNotification descrip-
tors specifies the handling of "buffered" Events, i.e. Events that have
been detected by the MG before the arrival of an EventsDescriptor, but
have not yet been notified to the MGC.

*    EventBufferProcessing specifies whether the buffered Events should
     be processed or discarded (the default is to process them.)

*    EventBufferNotification specifies whether the MG is expected to
     generate at most one notification (step by step), or multiple
     notifications (loop), in response to this request (the default is
     at most one.)

2.1.5.  Termination Descriptors

The LocalTerminationDescriptor and RemoteTerminationDescriptor parame-
ters describe the processing of the media flow in each of the direc-
tions. The actual properties of each descriptor depend on the Profiles



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specified for Termination Class.  Examples of Termination Classes are
RTP, Analog, DS0.  For an RTP Termination, for example, some of the pro-
perties might be:

*    IP address,

*    UDP ports (RTP and RTCP),

*    Encoding Method,

*    Packetization period,

The LocalTerminationDescriptor and RemoteTerminationDescriptor are
described in the form of an SDP descriptor which is part of the defini-
tion of a Profile.  These sets of properties can be enhanced by vendor
specific optional or mandatory extensions.  Properties in the LocalTer-
minationDescriptor and the RemoteTerminationDescriptor may be fully
specified, under-specified or (by omission) unspecified as described
above.

2.1.6.  Events, Signals and Packages

The MGC may ask to be notified about certain Events occurring on a Ter-
mination, e.g. off-hook Events, and a MGC may request certain Signals to
be applied to a Termination, e.g. dial-tone.

Events and Signals are grouped in Packages within which they share the
same namespace which we refer to as Event names. Packages are groupings
of the Events and that are related. For instance, one Package may sup-
port a certain group of Events and Signals for Simple analog access
lines, and another Package may support another group of Events and Sig-
nals for video lines. One or more Packages may applicable for a given
Termination Class, and part of the description of the Termination Class
consists of a list of supported Packages.

Event names are composed of two logical parts, a Package name and an
Event name. Examples of Package names are DTMF, MF, Trunk or Line. Exam-
ples of Event names are off hook, flash hook or "0" (the digit zero).

This document defines a basic set of Package names and Event names.
Additional Package names and Event names can be registered with the
IANA. A Package definition shall define the name of the Package, and the
definition of each Event belonging to the Package. The Event definition
shall include the precise name of the Event (i.e., the code used in the
MEGACO protocol), a plain text definition of the Event, and, went
appropriate, the precise definition of the corresponding Signals, for
example the exact frequencies of audio signal such as dial tones or DTMF
tones.



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Signals are divided into different types depending on their behavior:

*    On/off (OO)
     Once applied, these Signals last forever until they are turned off.
     This may happen either as the result of an Event or a new SignalRe-
     quests (see later).

*    Time-out (TO)
     Once applied, these Signals last until they are either turned off
     (by an Event or SignalRequests) or a Signal specific period of time
     has elapsed. Depending on Package specifications, a Signal that
     times out may generate an "operation complete" Event.

*    Brief (BR)
     The duration of these Signals is so short, that they stop on their
     own. If an Event occurs the Signal will not stop, however if a new
     SignalRequests is applied, the Signal will stop.

TO Signals are normally used to alert the Terminations' users, to signal
them that they are expected to perform a specific action, such as hang
down the phone (ringing). Transmission of these Signals should typically
be interrupted as soon as the first of the requested Events has been
produced.

2.1.7.  SignalDescriptors

A SignalDescriptor is a parameter that contains the set of Signals that
the MG is asked to apply to the Termination, such as, for example ring-
ing, or continuity tones. Signals are identified by their name, which is
an Event name, (and thus part of a Package)and may be qualified by pro-
perties.

If a Signal has already been attached to this Termination, the previous
Signal is removed, and the specified one is attached.  No Events which
would have occurred on the previous Signal will be generated subsequent
to a command that modifies the Signal descriptor, although the MGC may
not have received an Event from the previous Signal prior to sending the
command, and in fact the MG may have detected such an Event, but may not
have notified the MGC of it when it receives the new command.  The
behavior of the MG in such a circumstance is not defined.  It may send
the notification, or it may flush it.

2.1.8.  EventDescriptors

The EventDescriptor parameter contains a RequestIdentifier and a list of
Events that the MG is requested to detect and report. Such Events
include, for example, fax tones, continuity tones, or on-hook transi-
tion. The RequestIdentifier is used to correlate this request with the



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notifications that it may trigger.

To each Event is associated a notification action and an optional set of
embedded Events and Signal descriptors.  The notification actions are:

*    Notify the Event immediately, together with the accumulated list of
     observed Events,

*    Accumulate the Event in an Event buffer, but don't notify yet,

*    Accumulate according to a specified Digit Map,

*    Treat the Event according to a specific script,

*    Ignore the Event. (Events that are not specified in the descriptor
     are, by default, ignored.)

The embedded Signal descriptor, if present, is used as a replacement for
the current Signal descriptor.  It is possible, for example, to specify
that the dial-tone Signal be generated when an off-hook Event is
detected, or that the dial-tone Signal be stopped when a digit is
detected.  If no embedded Signal descriptor is specified, the production
of Signals continues as specified in the command.

The embedded Events descriptor, if present, is used as a replacement for
the current Event descriptor.  It is possible, for example, to specify
that DTMF digit collection starts as soon as an off-hook Event is
detected.

MEGACO Protocol implementations must be able to support at least one
level of embedding. An embedded Events descriptor that respects this
limitation shall not contain another Embedded Events descriptor.

2.1.9.  Digit Maps

The MGC can ask the MG to collect digits dialed by the user. This facil-
ity is intended to be used with residential gateways to collect the
numbers that a user dials; it may also be used with trunking gateways
and access gateways alike, to collect the access codes, credit card
numbers and other numbers requested by call control services.

An alternative procedure is for the MG to notify the MGC of the dialed
digits, as soon as they are dialed. However, such a procedure generates
a large number of interactions. It is preferable to accumulate the
dialed numbers in a buffer, and to transmit them in a single message.

The problem with this accumulation approach, however, is that it is hard
for the gateway to predict how many digits it needs to accumulate before



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transmission. For example, using the phone on our desk, we can dial the
following numbers:

        _______________________________________________________
       |  0                     |  Local operator             |
       |  00                    |  Long distance operator     |
       |  xxxx                  |  Local extension number     |
       |  8xxxxxxx              |  Local number               |
       |  #xxxxxxx              |  Shortcut to local number at|
       |                        |  other corporate sites      |
       |  *xx                   |  Star services              |
       |  91xxxxxxxxxx          |  Long distance number       |
       |  9011 + up to 15 digits|  International number       |
       |________________________|_____________________________|


The solution to this problem is to load the MG with a digit map that
correspond to the dial plan.

A digit map is defined by a name and a value.  The name is "visible"
within a scope, which can be the gateway itself, a hierarchical group of
Terminations, or a specific Termination.  Digit maps are provisioned
through standard Termination management operations such as Add, Modify,
Subtract or Move.  The scope of the digit map is determined by the name
of the Termination to which the command is applied:

*    If the command is applied to the "all" wildcarded Termination, the
     digit map is visible within the scope of the MG,

*    If the command is applied to a hierarchical name such as "Com1/3",
     the digit map becomes visible within all Terminations whose name
     begins with the specified prefix.

The DigitMapDescriptor contains a set of Digit Maps names and values to
be assigned:

*    A new digit map is created by specifying a name that is not yet
     defined at this level of the naming hierarchy. The value must be
     present.

*    A digit map value is updated by supplying a new value for a name
     that is already defined at this level of the naming hierarchy.
     Terminations using the map in an EventDescriptor when it is modi-
     fied continue to use the old value.  Subsequent EventDescriptors
     mentioning the DigitMap use the new value.

*    A digit map is deleted by supplying an empty value for a name that
     is already defined at this level of the naming hierarchy. A



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     wildcard naming convention can be used to delete all the digit maps
     associated with a specific Termination.

The MGC can determine defined digit maps with the Audit command.

The collection of digits according to a digit map may be protected by an
"interdigit timer", which can take two values:

-    If the gateway can determine that at least one more digit is
     requested for the digit string to match any of the allowed patterns
     in the digit map, then the timer value should be set to a long
     duration, such as 16 seconds.

-    If the digit map specifies that a variable number of additional
     digits may be needed (the "." indication at the end of a string),
     then the timer value should be set to a medium duration, such as 8
     seconds.

The "long interdigit timer" and the "short interdigit timer" are parame-
ters associated with a digit map.

The digit map mechanism is only used to reduce the number of messages
between the MG and the MGC.  It does not interpret or translate dialed
digits.  The MGC is free to not employ digit maps, and to request an
Event notification per digit.

2.1.10.  Statistics

The MG may maintain statistics that describe the status of the Termina-
tion. The precise properties of the statistics depends on the Class of
the Termination.

In the RTP class, the properties might include:

*    Number of packets sent:

*    Number of octets sent:

*    Number of packets received:

*    Number of octets received:

*    Number of packets lost:

*    Interarrival jitter:






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2.2.  Termination Management Commands

2.2.1.  Add

The Add commands adds a Termination to a Context.

            [TerminationId,]
            [LocalTerminationDescriptor,]
            [RemoteTerminationDescriptor,]
            <--- Add(TerminationId,
                     [TerminationState,]
                     [LocalTerminationDescriptor,]
                     [RemoteTerminationDescriptor,]
                     [EventsDescriptor,]
                     [SignalDescriptor,]
                     [DigitMapDescriptor])


TerminationId is the name of the Termination that is being added to the
Context. The TerminationId may be under-specified by using the "choose"
wildcard convention.  This convention must be used for packet Termina-
tions.  If the TerminationId is under-specified, the actual identifier
must be assigned by the MG and its complete value returned in the
response.

The TerminationState properties can be fully specified or unspecified by
the MGC. The MG uses the specified value when it is present.  The pro-
perty is unmodified if it is not mentioned

The LocalTerminationDescriptor properties can be either fully specified,
under-specified or unspecified by the MGC.  The MGC may under-specify a
parameter by providing a loose specification, such as a list of allowed
encoding methods or a range of packetization periods.  When the value
are under-specified, the MG returns a fully qualified LocalTermination-
Descriptor. When a value is unspecified, the MG does not change the
value of a property.  Since properties not in a Context have default
values, unspecified properties in an Add will have default values.

The RemoteTerminationDescriptor is the descriptor for the remote side of
a Termination, for example on the other side of the IP network. It
includes the same fields as in the LocalTerminationDescriptor, i.e. the
fields that describe a session according to the SDP standard. This
descriptor may be omitted when the information for the remote end is not
known yet. This information may be provided later via a Modify command.

Under-specified properties in RemoteTerminationDescriptor is possible
where the remote side has offered a choice, but the MG may have resource
restrictions which prevent the MGC from being able to make the choice.



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When the value of any properties in the descriptor are under-specified,
the MG returns a fully qualified RemoteTerminationDescriptor. When a
value is unspecified, the MG does not change the value as described
above.

Physical Terminations typically would not have a RemoteTermination-
Descriptor, but the Termination Class defines whether it does or does
not in all cases

After receiving an Add command that did not include a RemoteTermination-
Descriptor, a MG is in an ambiguous situation. Because it has received a
LocalTerminationDescriptor parameter, it can potentially receive pack-
ets. Because it has not yet received the RemoteTerminationDescriptor of
the other MG, it does not know whether the packets that it receives have
been authorized by the MGC. It must thus navigate between two risks,
i.e. clipping some important announcements or listening to potentially
unintelligible, or unauthorized data. The behavior of the MG is deter-
mined by the value of the Termination Mode element of the Termination-
State parameter:

*    If the mode was set to ReceiveOnly, the MG should accept the voice
     signals and transmit them through the Termination.

*    If the mode was set to Inactive, Loopback, Continuity Test, the MG
     should ignore the voice signals.

Note that the mode values SendReceive and SendOnly don't make sense in
this situation. They should be treated as errors, and the command should
be rejected.

The EventsDescriptor parameter, if present, provides the list of Events
that should be detected on the Termination.

The SignalDescriptor parameter, if present, provides the list of Signals
that should be produced on the Termination.

The command may also include a DigitMapDescriptor.  Each parameter
describes the name and the value of a digit map in the Context of the
Termination.

2.2.2.  Modify

The Modify command modifies the properties of a Termination.

            [LocalTerminationDescriptor,]
            [RemoteTerminationDescriptor,]
            <--- Modify(TerminationId,
                        [TerminationState,]



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                        [LocalTerminationDescriptor,]
                        [RemoteTerminationDescriptor,]
                        [EventsDescriptor,]
                        [SignalDescriptor,]
                        [DigitMapDescriptor])



TerminationId is the name of the Termination whose properties are being
modified. The TerminationId may not be under-specified.

The Modify command takes place within the Context to which the Termina-
tion belongs, or within the "null" Context when modifications are to be
made to the default values for the Termination.

The TerminationState properties can be fully specified or unspecified by
the MGC. The MG uses the specified value when it is present, the previ-
ous value otherwise.

The LocalTerminationDescriptor properties can be either fully specified,
under-specified or unspecified by the MGC.  The MGC may under-specify a
parameter by providing a loose specification, such as a list of allowed
encoding methods or a range of packetization periods.  When the value
are under-specified, the MG returns a fully qualified LocalTermination-
Descriptor. When a value is unspecified, the MG retains the previous
value.

The RemoteTerminationDescriptor properties can be either fully speci-
fied, under-specified, or left unspecified by the MGC.  When a value is
unspecified, the MG keeps the previous value. A value is under-
specified, the MG performs a selection and returns a RemoteTermination-
Descriptor that documents the choices made.

The EventsDescriptor parameter, if present, provides the list of Events
that should be detected on the Termination.

The SignalDescriptor parameter, of present, provides the list of signals
that should be produced on the Termination.

The command may also include a DigitMapDescriptor.  Each parameter
describes the name and the value of a digit map.

Modify of a Termination in the null Context changes the default values
for TerminationState, LocalTerminationDescriptor, RemoteTermination-
Descriptor, EventsDescriptor, and SignalDescriptor on that Termination.
Modify of a wildcarded termination ID in the null Context changes all
instances of the Termination covered by the wildcard specification.




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Modify of a TerminationID where only a subset of the hierarchy is named
(such as "com1/3" where com1 represents a channelized T3 as described
above), changes properties assigned to the logical unit covered by the
name specified.  In the example, changing "com1/3"'s "linecode = B8ZS"
would alter the line coding of one of the DS1s in the T3 to B8ZS.  Simi-
larly, changing the linecode of "com1/*" would change the line coding
for all DS1s in the T3.

Modify can also be used to program the MG to Notify the MGC at particu-
lar intervals if no other communication is occurring between the MGC and
the MG.  This has the effect of providing a heartbeat message from the
MG to the MGC.

2.2.3.  Subtract

The Subtract commands disconnects a Termination from a Context and
returns statistics on it.


    Statistics |
    *[TerminationId,
      Statistics]
    <---- Subtract(TerminationId,
                   [TerminationState,]
                   [EventsDescriptor,]
                   [SignalDescriptor,]
                   [DigitMapDescriptor])


TerminationId is the name of the Termination whose properties are being
modified. The TerminationId is either a fully specified value, or a
wildcard value indicating that all the terminations of a given Context
shall be removed.

When all Terminations have been removed from a specified Context, that
Context is deleted by the MG.

Ephemeral Terminations are deleted when they are removed from their Con-
text.  The Subtract command, when applied to an Ephemeral Termination,
shall not have any other parameter than the TerminationId.

The LocalTerminationDescriptor and RemoteTerminationDescriptor of a per-
manent termination are reset to their default value when the termination
is removed from its Context.

When applied to a Physical Termination, the Subtract command may include
TerminationState, EventsDescriptor, SignalDescriptor and DigitMap-
Descriptor parameters.  These parameters are processed as defined in the



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Modify command assuming a "null" Context, that is, they change the
default values of the Termination.

The command returns the statistics that were observed on the Termina-
tion.  When a wildcard is used, the command returns a Termination iden-
tifier and statistics for each of the Terminations whose name matched
the wildcard.

2.2.4.  Move

The Move command moves a Termination to another Context. The Termination
is removed from its old Context and is added to the new Context as an
atomic operation.  While this action appears similar to the packaging of
a subtract and an add command, it does not have the side effect of
deleting an Ephemeral Termination that the subtract command would cause.

            [LocalTerminationDescriptor,]
            [RemoteTerminationDescriptor]
            <-- Move(TerminationId,
                     [TerminationState,]
                     [LocalTerminationDescriptor,]
                     [RemoteTerminationDescriptor,]
                     [EventsDescriptor,]
                     [SignalDescriptor,]
                     [DigitMapDescriptor])

The TerminationId is the fully specified name of a Termination that is
being moved into the Context specified for the transaction.  The termi-
nation is subtracted from its previous Context.  If it was the last Ter-
mination in this previous Context, that Context is deleted.  A Context
with only one Termination is permitted.

The TerminationState, LocalTerminationDescriptor, RemoteTermination-
Descriptor, EventsDescriptor, SignalDescriptor, and DigitMapDescriptor
parameters are processed as in the Modify command.  Management Commands

2.2.5.  Audit

The Audit request returns properties associated with Terminations:












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            [TerminationId,]
            [TerminationState,]
            [LocalTerminationDescriptor,]
            [RemoteTerminationDescriptor,]
            [EventsDescriptor,]
            [SignalDescriptor,]
            [DigitMapDescriptor,]
            [Capabilities]
            [Statistics]
            <-- Audit (TerminationId,
                                  RequestedInfo)


The TerminationId is the name of the termination that is being audited.
The wildcard convention may be used. The command shall be applied either
in the null Context, for Terminations that are not part of an active
Context, or in the specific Context of the Termination(s).

The (possibly empty) RequestedInfo parameter describes the information
that is requested for the TerminationId specified. The following Termi-
nation info can be audited with this command:

     TerminationState, LocalTerminationDescriptor, RemoteTermination-
     Descriptor, EventsDescriptor, SignalDescriptor, ObservedEvents
     DigitMapDescriptor, Statistics and Capabilities.

The TerminationState, LocalTerminationDescriptor, RemoteTermination-
Descriptor, EventsDescriptor, SignalDescriptor, ObservedEvents and
DigitMapDescriptor values are the values currently used by the Termina-
tion.  ObservedEvents is as defined in Notify.

The Capabilities parameter returns values such as compression algo-
rithms, packetization period, connection networks that the MG is ready
to support for that Termination. In addition, the option can also be
used to return the Event Packages that the Termination supports, and the
list of TerminationState parameter values that the MG is ready to sup-
port for that Termination.

The Statistics parameter returns the current state of the Termination
statistics that would be generated on a Subtract.  This option provides
mid-call statistics.

If the RequestedInfo parameter is empty, Audit returns the TerminationID
only.  Combining this with using null and unspecified for ContextID and
wildcarding TerminationID, the Audit command can return a wide variety
of information:




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_________________________________________________________________________
|ContextID     TerminationID   Returns                                  |
|_______________________________________________________________________|
|Specific           all        List of terminations in a Context        |
|Specific        wildcard      List of terminations in a Context,       |
|                              whose name matches the wildcard          |
|Null            Root name     Audit of MG (base state & Events)        |
|Null               all        List of all Terminations in the MG       |
|Null              all/        List of all "highest order" Terminations |
|Null            wildcard      List of all Terminations whose           |
|                              name matches the wildcard.               |
|unspecified     Root name     Audit of MG (null Context)               |
|unspecified        all        List of all Terminations in the MG       |
|                              and the Context[s] to which they are     |
|                              associated (maybe null)                  |
|unspecified       all/        List of all "highest order" Terminations,|
|                              in the Context to which they are         |
|                              associated (maybe null)                  |
|unspecified     wildcard      List of all Terminations whose           |
|                              name matches the wildcard, in the        |
|                              Context[s] to which they are             |
|                              associated (maybe null)                  |
|_______________________________________________________________________|


The MGC can effect a "Are you alive" poll by using the Audit command on
the null Context with the Root name as the TerminationID and an empty
RequestedInfo. This will result in a short response from the MG.

2.3.  MG-Issued Commands

2.3.1.  Notify

                Notify (TerminationId,
                        ObservedEvents)


TerminationId is the name for the Termination in the MG which is issuing
the Notify command, as defined in section 2.1.2. The identifier must be
a fully qualified termination identifier. The local part of the name
must not use the wildcard convention.

ObservedEvents is a parameter that contains a RequestIdentifier and a
list of events that the MG detected in the order they have been
detected. The RequestIdentifier repeats the RequestIdentifier parameter
of the EventDescriptor that triggered this notification. It is used to
correlate this notification with the request that triggered it.




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The Events in the list must be reported in the order in which they were
detected. The list may only contain the identification of Events that
were requested in the RequestedEvents parameter of the triggering
EventsDescriptor. It must contain the Events that were either accumu-
lated (but not notified) or treated according to digit map (but no match
yet), and the final Event that triggered the detection or provided a
final match in the digit map.

Each element in the list must contain the name of the Event, and may
also contains properties associated with the Event and a notation of the
time at which the Event was detected. The MG MUST NOT send an unsoli-
cited notify.

There is an Event defined for all MGs that can be programmed with an
interval.  This Event can be used for a "heart beat" notify message from
MG to MGC.  Use of this Event is optional by the MGC.  Any message sent
by the MG to the MGC restarts the timer for the Event.

2.3.2.  ServiceChange

The ServiceChange command is used by the MG to signal that a Termina-
tion, or a group of Terminations, or the entire gateway, is  about to be
taken out of service, or has been brought back in to service.

             [MGCIdentity]
             <------- ServiceChange ( TerminationId,
                                ServiceChangeMethod,
                                ServiceChangeReason,
                                [ServiceChangeDelay])


The TerminationId identifies the Terminations that are taken in or out
of service.  The "all" wildcard convention may be used to apply the com-
mand to a group of Terminations, such as for example all Terminations
that are attached to a specified interface, or even all Terminations
that are attached to a given MG. The "choose" wildcard convention shall
not be used. Hierarchical names can be used to specify that an element
of a MG, such as for example a digital multiplex, is being brought out
of service.  The Root keyword indicates the gateway itself is restart-
ing.

The ServiceChangeMethod parameter specifies the type of ServiceChange.
Three values have been defined:

*    A "graceful" ServiceChange method indicates that the specified Ter-
     minations will Be taken out of service after the specified delay.
     The established connections are not yet affected, but the MGC
     should refrain from establishing new connections, and should try to



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     gracefully tear down the existing connections.  If is sent with the
     Root TerminationID, this message indicates the MG itself will be
     going out of service.

*    A "forced" ServiceChange method indicates that the specified Termi-
     nations were taken abruptly out of service. The established connec-
     tions, if any, are lost, although the Contexts are maintained.  The
     MGC should Subtract the Terminations which could return available
     statistics.  If is sent with the Root TerminationID, this message
     indicates the MG itself is out of service.

*    A "Restart" method indicates that service will be restored on the
     Terminations after the specified ServiceChangeDelay The Termina-
     tions are not currently attached to any Context.  If sent with the
     Root TerminationID, the MG is announcing its availability to the
     MGC.

*    A "Disconnected" method, always applied with the Root Termina-
     tionID, indicates that the MG lost communication with the MGC, but
     it was subsequently restored.  Since MG state may have changed, the
     MGC may wish to use the Audit command to resynchronize its state
     with the MG's.

ServiceChangeReason supplies the reason why the Termination is being
taken out of service or brought back into service.

The optional ServiceChangeDelay parameter is expressed as a number of
seconds. If the number is absent, the delay value should be considered
null.  In the case of the "graceful" method, a null delay indicates that
the MGC should simply wait for the natural termination of the existing
connections, without establishing new connections. The ServiceChangeDe-
lay is always considered null in the case of the "forced" method.

The MGC may return an MGCIdentity parameter that describes the MGC that
should preferably be contacted by the MG.  In this case the MG must
reissue the ServiceChange command to the new MGCIdentity

The ServiceChange command specifying the Root keyword for the Termina-
tionId is the registration command by which an MG announces its
existence to the MGC.  The MG is expected to be provisioned with the
name of one primary and some number of alternate MGCs.  The Servi-
ceChange method shall be "forced".  Acknowledgement of the ServiceChange
completes the registration process.

If an MG knows that a Termination is about to go out of service, it can
issue a ServiceChange with ServiceChangeMethod set to "graceful", and
specify a ServiceChangeDelay. If an MG has just detected that a Termina-
tion or a set of Terminations has just gone out of service, it issues a



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ServiceChange with ServiceChangeMethod set to "forced".

An MGC may inform an MG that it should send subsequent commands to
another MGC by returning the identity of a new MGC when responding to
ServiceChange. The MG may need to reissue ServiceChange to the new MGC.

2.4.  The following table lists the defined commands, and the available
input parameters.  An "X" denotes the parameter is legal for the command

   __________________________________________________________________
   __________________________________________________________________
  |                  Add   Sub   Mdfy   Move   Audt   Ntfy   SvcChng|
  | TermID            X     X     X      X      X      X        X   |
  | TermState         X     X     X      X                          |
  | LocalTermDesc     X     X     X      X                          |
  | RemoteTermDesc    X     X     X      X                          |
  | EventsDesc        X     X     X      X                          |
  | SignalDesc        X     X     X      X                          |
  | DigitMapDescr     X     X     X      X                          |
  | RequestedInfo                               X                   |
  | ObservedEvents                                     X            |
  | SvcChngMethod                                               X   |
  | SvcChngReason                                               X   |
  | SvcChngDelay                                                X   |
  |_________________________________________________________________|


3.  MG-MGC Control Associations

An MG is under control of (one or more) MGCs.  The control association
between MG and MGC is initiated at MG cold start, and announced by a
ServiceChange message, but can be changed by subsequent events, such as
failures or manual service events.  While the protocol does not have an
explicit mechanism to support multiple MGCs controlling an MG, it has
been designed to support the following model, which has impacts on how
protocol mechanisms are used in such a case.

3.1.  Multiple MGCs per MG

There are several circumstances where it is desired that an MG be con-
trolled by more than one MGC.  One is the case where  different MGCs
have varying abilities, for example, one MGC may be capable of SS7
interwork, another may only be capable of H.323 interwork.  A physical
MG may need some of it's trunks controlled by SS7, while others are con-
trolled by H.323.

The model supported by the protocol is statically allocated partitioning
of Terminations.  In this model, a physical MG can be thought of as



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multiple virtual MGs, each with a non-intersecting set of Terminations.
The model does not require that other resources be statically allocated,
just Terminations.  The mechanism for allocating Terminations to virtual
MGs is a management method outside the scope of the protocol.  Each of
the virtual MGs appears to the MGC as a complete implementation of the
MEGACOP client.

In many cases, a physical MG may have only one network interface, which
Must be shared across virtual MGs.  In such a case, the packet/cell side
Termination is shared.  It should be noted however, that in use, such
interfaces require an ephemeral instance of the Termination to be
instantiated per flow, and thus sharing the Termination is straightfor-
ward.  This mechanism does lead to a complication, namely that the MG
must always know which of its controlling MGCs should be notified if an
event occurs on the interface.

In normal operation, the MG will be instructed by the MGC to create net-
work flows (if it is the originating side), or to expect flow requests
(if it is the terminating side), and no confusion will arise.  However,
if an unexpected event occurs, the MG must know what to do.

If recovering from the event requires manipulation of the interface
state, there can be only one MGC who can do so.  These issues are
resolved by allowing any of the MGCs to create EventDescriptors to be
notified of such events, but only one MGC can have read/write access to
the physical interface properties; all other MGCs have read-only access.
The management mechanism is used to designate which MGC has read/write
capability, and is designated the Master MGC.

Each virtual MG has it's own Root Termination.  In most cases the values
for the properties of the Root Termination are independently settable by
each MGC.  Where there can only be one value, the parameter is read-only
to all but the Master MGC.

3.2.  Cold Start

An MG is pre-provisioned by a management mechanism outside the scope of
This protocol with a Primary and (optionally) an ordered list of Secon-
dary MGCs.  Upon a cold start of the MG, it will issue a ServiceChange
command with a "Restart" method, on the Root Termination to it's primary
MGC.  If the MGC accepts the MG, it will send a Transaction Accept, with
the MGCIdenty set to itself.  If the MG recieves an an MGCIdentity not
equal to the MGC it contacted, it sends a ServiceChange to the MGC
specified in the MGCIdentity.  It continues this process until it gets a
controlling MGC to accept its registration, or it fails to get a reply.






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3.3.  Upon failure to obtain a reply, either from the Primary MGC, or a
designated successor, the MG tries it's pre-provisioned Secondary MGCs,
in order.

3.4.  Failover

3.4.1.  Failure of an MG

If an MG fails, but is capable of sending a message to the MGC, it sends
a ServiceChange with an appropriate method (graceful or forced) and
specifies the root TerminationID.  When it returns to service, it sends
a ServiceChange with a "Restart" method.

Pairs of MGs that are capable of redundant failover of one of the MGs
are accommodated by allowing the MGC to send duplicate messages to both
MGs.  Only the Working MG must accept or reject transactions.  Upon
failover, the Protect MG sends a ServiceChange command with a "Failover"
method and a "Failed MG" reason.  The MGC then uses the Protect MG as
the active MG, and only it must accept/reject transactions.  When the
error condition is repaired, the Working MG can send a "ServiceChange"
with a "Restart" method.

3.4.2.  Failure of an MGC

If the MG notices a failure of it's controlling MGC, it attempts to con-
tact the next MGC on its pre-provisioned list.  It starts it's attempts
at the beginning (Primary MGC), unless that was the MGC that failed, in
which case it starts at it's first Secondary MGC.  It sends a Servi-
ceChange message with a "Failover" method and a "Failed MGC" reason.

In partial failure, or manual maintenance reasons, an MGC may wish to
Direct its controlled MGs to use a different MGC.  To do so, it sets the
"ControllingMGC" property of the root Termination to its new MGC.  As a
side effect, the MG should send a ServiceChange message with a "Forced"
method and a "MGC directed change" reason to the designated MGC.  If it
fails to get a reply, or fails to see an Audit command subsequently, it
should behave as if it's MGC failed, and start contacting secondary
MGCs.

When the MGC initiates a failover, the handover should be transparent to
Operations on the gateway.  Commands in progress continue, transaction
replies are sent to the new MGC, and the MG should expect outstanding
transaction replies from the new MGC.  All connections should stay up.

It is possible that the MGC could be implemented in such a way that a
failed MGC is replaced by a working MGC where the identity of the new
MGC is the same as the failed one.  In such a case, "ControllingMGC"
would be replaced with the previous value.  In such a case, the MG shall



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behave as if the value was changed, and send a ServiceChange message, as
above.

Pairs of MGCs that are capable of redundant failover can notify the con-
trolled MGs of the failover by the above mechanism.

3.5.  Error Codes

All MEGACO Protocol commands are acknowledged. The acknowledgment car-
ries a return code, which indicates the status of the command. The
return code is value for which three ranges have been defined:

*    successful completion,

*    transient error,

*    permanent error.

4.  Security Considerations

If unauthorized entities could use the MEGACO protocol, they would be
able to set-up unauthorized calls, or to interfere with authorized
calls. The primary security mechanism employed by the protocol is IPSEC
[RFC2401].  Support of the AH header [RFC2402] affords authentication
and integrity protection on messages passed between the MG and the MGC.
Support of the ESP header [RFC2406] can provide confidentiality of mes-
sages if desired.

Implementation of IPSEC requires that the AH and ESP headers be inserted
between the IP and UDP headers.  This presents an implementation problem
for MEGACO protocol implementations where the underlying network imple-
mentation does not support IPSEC.  As an interim solution, the MEGACO
protocol defines an optional AH header within the protocol header.  The
header fields are exactly those of the AH header as defined in
[RFC2402].  The semantics of the header fields are the same as the
"transport mode" of [RFC2402], except for the calculation of the
Integrity Check Value (ICV).  In IPSEC, the ICV is calculated over the
entire IP packet including the IP header.  This prevents spoofing of the
IP addresses.  To retain the same functionality, the ICV calculation
should be performed across the entire MEGACOP message prepended by a
synthesized IP header consisting of a 32 bit source IP address, a 32 bit
destination address and an 16 bit UDP port in the MSBs of a 32 bit word.
The Authentication Data is assumed to be zero as in [RFC2402].  The
"Next Header" and "RESERVED" fields MUST be set to "zero".

The ICV calculation is thus performed over a structure that would look
like:




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         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                      Source IP Address                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                   Destination IP Address                      |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |            UDP Port           |               RESERVED        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |  Next Header  |  Payload Len  |          RESERVED             |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                 Security Parameters Index (SPI)               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                    Sequence Number Field                      |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        +               Authentication Data (variable)                  +
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        +                 message contents (variable)                   +
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


When the AH-within-MEGACO mechanism is employed when TCP is the tran-
sport Layer for MEGACOP, the UDP Port above becomes the TCP port, and
all other operations are the same.

Implementations of the MEGACO protocol using IPv4 MUST support the
interim AH-within-MEGACO scheme.  Implementations SHOULD implement IPSEC
AH header if the underlying network system supports it.  Implementations
MAY support the ESP header.  IPSEC and AH-within-MEGACO MUST NOT be used
at the same time.  IPv6 Implementations are assumed to have IPSEC imple-
mentations and MUST NOT use the AH-within-MEGACO scheme.

When employing the AH header, either in IPSEC or AH-within-MEGACO, all
implementations of the protocol MUST implement section 5 of [RFC2402]
which defines a minimum set of algorithms for integrity checking using
manual keys.  MECACOP implementations SHOULD implement IKE [RFC2409] to
permit more robust keying options.  MEGACOP implementations employing
IKE SHOULD implement RSA signatures and authentication with RSA public
key encryption.  MECACOP implementations employing the ESP header
[RFC2406] MUST implement section 6 of [RFC2406] which defines a minimum
set of algorithms for integrity checking and encryption.

NOTE: The AH-within-MEGACO scheme is defined as interim.  The next



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version of this protocol is likely to deprecate it (backwards compati-
bility?).

Adequate protection of the connections must be achieved if the MG and
the MGC only accept messages for which authentication services of the AH
header have been configured.  Employing the ESP header for encryption
service must provide additional protection against eavesdropping, thus
forbidding third parties from monitoring the connections set up by a
given Termination

The encryption service should also be requested if the session descrip-
tions are used to carry session keys, as defined in SDP.

These procedures do not necessarily protect against denial of service
attacks by misbehaving MGs or misbehaving MGCs. However, they will pro-
vide an identification of these misbehaving entities, which should then
be deprived of their authorization through maintenance procedures.

Also note that the use of NAT (Network Address Translation) interferes
with the operation IPSEC and IPSEC-like mechanisms, as they modify IP
addresses and port numbers, and thus invalidate the ICV calculations.
It is possible to use IPSEC between the point at which NAT is applied
and the outside party.

4.1.  Protection of Media Connections

The protocol allows the MGC to provide MGs with "session keys" that can
be used to encrypt the audio messages, protecting against eavesdropping.

A specific problem of packet networks is "uncontrolled barge-in."  This
attack can be performed by directing media packets to the IP address and
UDP port used by a connection. If no protection is implemented, the
packets must be decompressed and the signals must be played on the "line
side".

A basic protection against this attack is to only accept packets from
known sources, checking for example that the IP source address and UDP
source port match the values announced in the RemoteTerminationDescrip-
tor But this has two inconveniences: it slows down connection establish-
ment and it can be fooled by source spoofing:

*    To enable the address-based protection, the MGC must obtain the
     remote session description of the egress MG and pass it to the
     ingress MG.  This requires at least one network roundtrip, and
     leaves us with a dilemma: either allow the call to proceed without
     waiting for the round trip to complete, and risk for example,
     "clipping" a remote announcement, or wait for the full roundtrip
     and settle for slower call-set-up procedures.



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*    Source spoofing is only effective if the attacker can obtain valid
     pairs of source destination addresses and ports, for example by
     listening to a fraction of the traffic. To fight source spoofing,
     one could try to control all access points to the network.  But
     this is in practice very hard to achieve.

An alternative to checking the source address is to encrypt and authen-
ticate the packets, using a secret key that is conveyed during the call
set-up procedure. This will not slow down the call set-up, and provides
strong protection against address spoofing.









































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5.  Syntax

Editor's Note: In this edition of the document, a decision has not
been made on the encoding of the protocol.  The following EBNF
description is therefore somewhat awkward.  Productions with the word
"Token" are not defined.  In an ASCII encoding, they would typically be
some kind of keyword and a separator.  In a binary encoding, they would
be a code.  The productions use the terms "digit", as in 9DIGIT, which
would be understood as a 9 character numeric string in ASCII, or a 32 bit
number in binary, although there may be small differences in coding
when the decision is actually made.  The syntax leaves out separators and
whitespace which would be necessary in an ASCII encoding.  It leaves out
length fields, which may be necessary in a binary encoding.

megacoMessage = authenticatedMessage / message

authenticatedMessage = authToken authenticationHeader message

authenticationHeader = ; as defined in RFC []

message = SystemID *(transactionRequest / transactionAccept /
                     transactionReject)
; question of whether SystemID is there at all
; Version might be in registration in msg header if here

transactionRequest = transToken transactionId 1*Action
transactionAccept = acceptToken transactionId 1*ActionAccept
transactionReject = rejectToken transactionId 1*ActionReject

ActionAccept =   ctxToken contextId *commandAccept
commandAccept = commandName [terminationId] *(parameters)

ActionReject = ctxToken contextID *commandReject
CommandReject = commandName [terminationID] errorMessage
errorMessage = errorCode errorText
errorCode = OCTET STRING(3)  ;could be extended
errorText = OCTET STRING

transactionId = INTEGER32
SystemId = domainName [":" portNumber]
domainName = 1*256(ALPHA / DIGIT / "." / "-") ; as defined in RFC 821
portNumber = INTEGER16   ;should this be 5digit, 16 bit?

version = megacopToken Version Profile
Version = OCTET STRING
Profile = OCTET STRING ;need explanation

Action = ctxToken contextId 1*command



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contextId = nullToken / unspecifiedToken / INTEGER32

command = commandName terminationId parameters

commandName = (addToken /
        subtractToken /
        modifyToken   /
        moveToken     /
        auditToken    /
        notifyToken   /
        serviceChangeToken )

terminationId = "." /  LocalNamePart /
                LocalNamePart *("/"LocalNamePart)

LocalNamePart = AnyNameToken / AllNameToken / NameString

AnyName = "$"

AllNames = "*"

NameString = 1*(SuitableCharacters)

parameters = ([ TSToken TerminationState ]
              [LTToken LocalTerminationDescriptor ]
              [RTToken RemoteTerminationDescriptor ]
              [EDToken EventsDescriptor ]
              [SDToken SignalDescriptor ]
              [DMToken DigitMapDescriptor ]
              [RIToken RequestedInfo ]
              [RMToken ServiceChangeMethod ]
              [RDToken ServiceChangeDelay ]
              [OEToken ObservedEvents ]
              [STToken Statistics ]
              [CpToken Capabilities ]
              [MiToken MGCIdentity ]
              *[extensionParameterToken parameterValue] ])  ;fix
TerminationState = stateParameter   ;leftover production for bracketing
stateParameter = ([modeToken TerminationMode]
                  [bufferedEventHandlingToken BufferedEventHandling ])
                                ;fix, there are 2 of them
TerminationMode = sendonlyToken / recvonlyToken / sendrecvToken /
      inactiveToken / loopbackToken / conttestToken  / OutOfService
BufferedEventHandling = loopControl / processControl / ;fix
              (loopControl processControl )
loopControl = stepToken / loopToken
processControl = processToken / discardToken




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LocalTerminationDescriptor = TerminationDescriptor
RemoteTerminationDescriptor = TerminationDescriptor

eventName = [ (packageName / "*") "/" ] (eventId / "all" / eventRange)
packageName = 1*(SuitableCharacters)
eventId = 1*(SuitableCharacters) ;could be an Integer32
EventsDescriptor = [requestedEvent 0*(requestedEvent)]
requestedEvent = eventName  [0*(eventParameters)] [requestedActions]
eventParameters = *(parameterName parameterValue)
requestId = INTEGER32

eventRange = "[" 1*(DIGIT / DTMFLetter / "*" / "#" /
                   (DIGIT "-" DIGIT)/(DTMFLetter "-" DTMFLetter)) "]"
           ;may want to remove the above

requestedActions = requestedAction [ embeddedSignalEvent ]
                   [ mediaAction ]
requestedAction = NotifyActionToken / AccumlateToken /
                  AccumulateByDigitMapToken digitMapName /
                  ScriptToken scriptName
embeddedSignalEvent = [EventDescriptorToken EventsDescriptor ]
                      [SignalDescriptorToken SignalDescriptor ]
mediaAction = SToken

SignalDescriptor = [ SignalRequest 0*(SignalRequest) ]
SignalRequest = eventName [eventParameters ]
eventParameters = eventParameter 0*( eventParameter )
eventParameter = eventParameterString / quotedString
eventParameterString = 1*()

DigitMapDescriptor = digitMapName DigitMapValue
digitMapName = STRING
DigitMapValue = ["L:" longTimer ","] ["M:" mediumTimer ","] DigitMap
longTimer = 1*2DIGIT
shortTimer = 1*2DIGIT
DigitMap = DigitString  / "(" DigitStringList ")"
DigitStringList = DigitString *( "|" StringList )
DigitString = 1*(DigitStringElement)
DigitStringElement = DigitPosition ["."]
DigitPosition = DigitMapLetter / DigitMapRange
DigitMapLetter = DIGIT / "#" / "*" / "A" / "B" / "C" / "D" / MFSig / "T"
MFSig = "K0" / "K1" / "K2" / "S0" / "S1" / "S2" / "S3" /
DigitMapRange =  "x" / "[" DigitLetters "]"
DigitLetter  = *((DIGIT "-" DIGIT ) / DigitMapLetter)

RequestedInfo = [infoCode 0*(infoCode)]
infoCode = TerminationStateToken / LocalTermDescToken / RemoteTermDescToken /
           EventDeccToken / SignalDescToken /



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           DigMapToken / StatsToken / ObsrvdEvntsToken CapsToken /
ServiceChangeMethod = GracefulToken / ForcedToken / RestartToken / FailoverToken
ServiceChangeDelay = INTEGER32

ObservedEvents = (requestId [ observedEvent *(observedEvent) ])
observedEvent = [ TimeNotation ] SignalRequest
TimeNotation= INTEGER64; 64 bits NTP time stamp ?

Statistics = [StatisticsParameter 0*( StatisticsParameter ) ]
StatisticsParameter = ( PktsSentToken packetsSent )
                    / ( OctetsSentToken octetsSent )
                    / ( PktsRecvdToken packetsReceived )
                    / ( OctetsRecvdToken octetsReceived )
                    / ( PktsLostToken packetsLost )
                    / ( JitterToken jitter )
                    / ( AvgLatencyToken averageLatency )
                    / ( StatisticsParameterExtensionName
                        StatisticsParameterExtensionValue )
packetsSent = INTEGER64
octetsSent = INTEGER64
packetsReceived = INTEGER64
octetsReceived = INTEGER64
packetsLost = INTEGER32
jitter = INTEGER32
averageLatency = INTEGER32
StatisticsParameterExtensionName = "X" "-" 2*ALPHA ;fix
StatisticsParameterExtensionValue = INTEGER32

extensionParameter = "X" ("-"/"+") 1*6(ALPHA / DIGIT)
parameterString = 1*(%x20-7F)

Capabilities = ;not defined yet

MGCIdentity = SystemId


SuitableCharacter= DIGIT / ALPHA / "+" / "-" / "_" / "&" /
                   "!" / "'" / "|" / "=" / "#" / "?" / "/" /
                   "." / "$" / "*" / ";" / "@" / "[" / "]" /
                   "^" / "`" / "{" / "}" / "~"
quotedString = DQUOTE visibleString
                 0*(quoteEscape visibleString) DQUOTE
quoteEscape = DQUOTE DQUOTE
visibleString = (%x00-21 / %x23-FF)

TerminationDescriptor = ;Undecided, could be SDP as in RFC 2327





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5.1.  Termination Names

Each command contains a unique Termination name. The following rules for
construction and interpretation of the Termination names MUST be sup-
ported:

1)   The individual terms of the naming path MUST be separated by a sin-
     gle slash ("/", ASCII 2F hex).

2)   The individual terms are character strings composed of letters,
     digits or other printable characters, with the exception of charac-
     ters used as delimiters ("/", "@"), characters used for wildcarding
     ("*", "$") and white spaces.

3)   Wild-carding is represented either by an asterisk ("*") or a dollar
     sign ("$") for the terms of the naming path which are to be wild-
     carded.  Thus, if the full naming path looks like

             term1/term2/term3

     then the Termination name looks like this depending on which terms
     are wild- carded:

             */term2/term3 if term1 is wild-carded
             term1/*/term3 if term2 is wild-carded
             term1/term2/* if term3 is wild-carded
             term1/*/* if term2 and term3 are wild-carded,
              etc.


     In each of these examples a dollar sign could have appeared instead
     of an asterisk.

4)   A term represented by an asterisk is to be interpreted as: "use ALL
     values of this term known within the scope of the Media Gateway".
     A term represented by a dollar sign is to be interpreted as: "use
     ANY ONE value of this term known within the scope of the Media
     Gateway".  The description of a specific command may add further
     criteria for selection within the general rules given here.












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             Examples of TerminationId:

             /MG7.network.com/com1/channel1  ;  fully qualified Termination name


                              ;  one channel on device "com1"

                              ;  channels on device "com1"

                              ;   all devices on MG

                              ;  on all devices on MG


When an Ephemeral Termination is to be created, the desired termination
type is specified as the first component of the name with "/$" con-
catenated on the name.  For example, "RTP/$" would request a new Termi-
nation from the RTP Termination Class.

5.2.  Events, Signals and Packages

Event names are case insensitive and are composed of two logical parts,
a Package name and an Event name. Both names are strings of letters,
hyphens and digits, with the restriction that hyphens shall never be the
first or last characters in a name. Package or Event names are not case
sensitive - values such as "hu", "Hu", "HU" or "hU" should be considered
equal.

In textual representations, the Package name, when present, is separated
from the Event name by a slash ("/").  The Package name is in fact
optional. Each termination-type has a default Package associated with
it, and if the Package name is excluded from the Event name, the default
Package name for that termination-type is assumed. For example, for an
analog access line, the following two Event names are equal:

l/dl dial-tone in the line Package for an analog access line.

dl   dial-tone in the line Package (default) for an analog access line.

This document defines a basic set of Package names and Event names.
Additional Package names and Event names can be registered with the
IANA. A Package definition shall define the name of the Package, and the
definition of each Event belonging to the Package. The Event definition
shall include the precise name of the Event (i.e., the code used in the
MEGACO protocol), a plain text definition of the Event, and, went
appropriate, the precise definition of the corresponding signals, for
example the exact frequencies of audio signal such as dial tones or DTMF



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tones.

In addition, implementers can gain experience by using experimental
Packages. The names of experimental Packages must start with the two
characters "x-"; the IANA shall not register Package names that start
with these characters.

Digits, or letters, are supported in many Packages, notably "DTMF", "MF"
and "pulse". Digits and letters are defined by the rules "Digit" and
"Letter" in the definition of digit maps. This definition refers to the
digits (0 to 9), to the asterisk or star ("*") and orthotrope, number or
pound sign ("#"), and to the letters "A", "B", "C" and "D", as well as
the timer indication "T". These letters can be combined in "digit
string" that represent the keys that a user punched on a dial. In addi-
tion, the letter "X" can be used to represent all digits, and the sign
"$" can be used in wildcard notations. The need to easily express the
digit strings has a consequence on the form of Event names:

     An Event name that does not denote a digit should always contain at
     least one character that is neither a digit, nor one of the letters
     A, B, C, D, T or X. (Such names should not contain the special
     signs "*", "#", "/" or "$".)

An MGC may often have to ask a MG to detect a group of Events. Two con-
ventions can be used to denote such groups:

*    The wildcard convention can be used to detect any Event belonging
     to a Package, or a given Event in many Packages, or Event any Event
     in any Package supported by the MG.

*    The regular expression Range notation can be used to detect a range
     of digits.

The star sign (*) can be used as a wildcard instead of a Package name,
and the dollar sign ("$") or the keyword "all" can be used as a wildcard
instead of an Event name:

     A name such as "foo/all" denotes all Events in Package "foo"
     A name such as "*/bar" denotes the Event "bar" in any Package sup-
     ported by the MG
     The names "*" or "*/all" denote all Events supported by the MG.

The MGC can ask an MG to detect a set of digits or letters either by
individually describing those letters, or by using the "range" notation
defined in the syntax of digit strings. For example, the MGC can:

     Use the letter "x" to denote "any letter or digit."
     Use the notation "[0-9#]" to denote the digits 0 to 9 and the pound



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     sign.

Events and Signals are described in Packages. The Package description
must provide, for each Event, the following information:

*    The description of the Event and its purpose, which should mean the
     actual Signal that is generated by the client (i.e., xx ms FSK
     tone) as well as the resulting user observed result (i.e., MW light
     on/off).

*    The detailed characteristics of the Event, such as for example fre-
     quencies and amplitude of audio signals, modulations and repeti-
     tions,

*    The typical and maximum duration of the Event.

Package descriptions should describe, for all Signals, their type (OO,
TO, BR). They should also describe the maximum duration of the TO Sig-
nals.

5.3.  Digit Maps

A digit map is expressed using a syntax derived from the Unix system
command, egrep. For example, the dial plan described above in section 2
results in the following digit map:

         (0T| 00T|[1-7]xxx|8xxxxxxx|#xxxxxxx|*xx|91xxxxxxxxxx|9011x.T)


The "DigitMapValue" rule of protocol syntax describes a format that con-
tains three parameters:

*    An optional notation of a "Long Timer," in seconds,

*    An optional notation of a "Medium Timer," in seconds,

*    The actual expression of the map.

The timer parameters are optional.  When they are not specified, default
values are assumed.  Suggested default values are 16 seconds for the
long timer, 8 seconds for the medium timer.

A DigitMap, according to this syntax, is defined either by a "string" or
by a list of strings. Each string in the list is an alternative number-
ing scheme. Each element in the string is composed of a set of string
elements, each of which can optionally be followed by a repetition char-
acter. The possible elements are:




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*    A digit,

*    The special characters "#" and "*" (number sign and star sign),

*    The letters A, B, C or D,

*    The symbols "K0",  "K1", "K2", "S0", "S1", "S2" and "S3", which may
     be used in MF signalling,

*    A range notation such as "[0-9]" or "[0-9*#]", that would be
     matched by a single occurence of any letter in the range,

*    The character "x", that would be matched by any digit between 0 and
     9.

Each element may be followed by the repetition symbol "." (dot), to
denote a variable number of occurences of the position.

A MG that detects digits, letters or timers must:

1)   Add the Event parameter code as a token to the end of an internal
     state variable called the "current dial string"

2)   Apply the current dial string to the digit map table, attempting a
     match to each regular expression in the Digit Map in lexical order

3)   If the result is under-qualified (partially matches at least one
     entry in the digit map), do nothing further.

If the result matches, or is over-qualified (i.e. no further digits
could possibly produce a match), notify the currently accumulated Events
to the MGC, in the order in which they occurred.

When an MG is unable to store a digit map, it shall return an error to
the MGC.

5.4.  Statistics

The MG may maintain statistics that describe the status of the Termina-
tion. The precise properties of the statistics depends on the Class of
the Termination.

In the RTP Class, the some the properties are:

     Number of packets sent:
     The total number of RTP data packets transmitted by the sender
     since starting transmission on this connection. The count is not
     reset if the sender changes its synchronization source identifier



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     (SSRC, as defined in RTP), for example as a result of a Modify com-
     mand. The value is zero if the connection was set in "receive only"
     mode.

     Number of octets sent:
     The total number of payload octets (i.e., not including header or
     padding) transmitted in RTP data packets by the sender since start-
     ing transmission on this connection. The count is not reset if the
     sender changes its SSRC identifier, for example as a result of a
     Modify command. The value is zero if the connection was set in
     "receive only" mode.

     Number of packets received:
     The total number of RTP data packets received by the sender since
     starting reception on this connection. The count includes packets
     received from different SSRC, if the sender used several values.
     The value is zero if the connection was set in "send only" mode.

     Number of octets received:
     The total number of payload octets (i.e., not including header or
     padding) transmitted in RTP data packets by the sender since start-
     ing transmission on this connection. The count includes packets
     received from different SSRC, if the sender used several values.
     The value is zero if the connection was set in "send only" mode.

     Number of packets lost:
     The total number of RTP data packets that have been lost since the
     creation of the RTP connection. This number is defined to be the
     number of packets expected less the number of packets actually
     received, where the number of packets received includes any which
     are late or duplicates. The count includes packets received from
     different SSRC, if the sender used several values. Thus packets
     that arrive late are not counted as lost, and the loss may be nega-
     tive if there are duplicates. The count includes packets received
     from different SSRC, if the sender used several values. The number
     of packets expected is defined to be the extended last sequence
     number received, as defined next, less the initial sequence number
     received. The count includes packets received from different SSRC,
     if the sender used several values. The value is zero if the connec-
     tion was set in "send only" mode. This property is omitted if the
     connection was set in "data" mode.

     Interarrival jitter:
     An estimate of the statistical variance of the RTP data packet
     interarrival time measured in milliseconds and expressed as an
     unsigned integer. The interarrival jitter J is defined to be the
     mean deviation (smoothed absolute value) of the difference D in
     packet spacing at the receiver compared to the sender for a pair of



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     packets. Detailed computation algorithms are found in RFC 1889. The
     count includes packets received from different SSRC, if the sender
     used several values. The value is zero if the connection was set in
     "send only" mode. This property is omitted if the connection was
     set in "data" mode.

     Average transmission delay:
     An estimate of the network latency, expressed in milliseconds. This
     is the average value of the difference between the NTP timestamp
     indicated by the senders of the RTCP messages and the NTP timestamp
     of the receivers, measured when this messages are received. The
     average is obtained by summing all the estimates, then dividing by
     the number of RTCP messages that have been received. This property
     is omitted if the connection was set in "data" mode.
     When the MG's clock is not synchronized by NTP, the latency value
     can be computed as one half of the round trip delay, as measured
     through RTCP.
     When the MG cannot compute the one way delay or the round trip
     delay, the property conveys a null value.

For a detailed definition of these variables, refer to RFC 1889.

When the connection was set up over an ATM network, the meaning of these
properties may change:

     Number of packets sent:
     The total number of ATM cells transmitted since starting transmis-
     sion on this connection.

Number of octets sent:
     The total number of payload octets transmitted in ATM cells.

Number of packets received:
     The total number of ATM cells received since starting reception on
     this connection.

Number of octets received:
     The total number of payload octets received in ATM cells.

Number of packets lost:
     Should be determined as the number of cells lost, or set to zero if
     the adaptation layer does not enable the MG to assess losses.

Interarrival jitter:
     Should be understood as the interarrival jitter between ATM cells.

Average transmission delay:
     The MG may not be able to assess this property over an ATM network.



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     It could simply report a null value.

When the Termination is of type TDM or analog, the meaning of these pro-
perties is defined as follow:

     Number of packets sent:
     Not significant.

Number of octets sent:
     The total number of payload octets transmitted over the local con-
     nection.

Number of packets received:
     Not significant.

Number of octets received:
     The total number of payload octets received over the connection.

Number of packets lost:
     Not significant.  A value of zero is assumed.

Interarrival jitter:
     Not significant.  A value of zero is assumed.

Average transmission delay:
     Not significant.  A value of zero is assumed.

5.5.  Examples

The following examples use, for practical reasons, a text representation
of the MEGACO protocol. This representation assumes the following token
definitions:

           __________________________________________________
          | TRAN    |  transToken                           |
          | ACPT    |  acceptToken                          |
          | MEGACO  |  megacopToken                         |
          | CTX     |  ctxToken                             |
          | ADD     |  addToken                             |
          | SUBTRACT|  subtractToken                        |
          | MODIFY  |  modifyToken                          |
          | TS      |  TSToken (TerminationState)           |
          | LT      |  LTToken (LocalTerminationDescriptor) |
          | RT      |  RTToken (RemoteTerminationDescriptor)|
          |_________|_______________________________________|






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5.5.1.  Example Add transaction:

        TRAN 12345678 MGC1.network.com:12345 MEGACOP 1.0
        CTX= -1
        ADD= circuitgroup1/5
        LS= {m=recvonly
        }
        ADD= RTP/ANY
        LS= {m=sendrecv
        }
        LT= {v=0
        c=IN IP4 100.100.100.089
        m=audio ANY RTP/AVP 0
        }
        RT= {v=0
        c=IN IP4 200.200.200.133
        m=audio 4321 RTP/AVP 0
        }


5.5.2.  Example response to Add transaction:

        ACPT 12345678 MG1.network.com:12345 MEGACOP 1.0
        CTX= 12344321
        ADD= circuitgroup1/5
        ADD= RTP/7777
        LT= {v=0
        c=IN IP4 100.100.100.089
        m=audio 3456 RTP/AVP 0
        }


5.5.3.  Example Modify transaction:

        TRAN 12345672 MGC1.network.com:12345 MEGACOP 1.0
        CTX= 12344321
        MODIFY= circuitgroup1/5
        LS= {m=sendrecv
        }


5.5.4.  Example Subtract transaction:

        TRAN 12345673 MGC1.network.com:12345 MEGACOP 1.0
        CTX= 12344321
        SUBTRACT= circuitgroup1/5
        SUBTRACT= RTP/7777




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5.6.  Transaction Response Codes

All MegacoP transactions return a transaction response code which ack-
nowledges the command(s) sent and returns a code indicating the success
or failure of the command.

The transaction response code is an integer number, the first digit of
which indicates the class of the Response Code.

        2xx: Success -- the transaction was successfully received, understood, and
                all commands were executed;

        4xx: Protocol reject -- the transaction received could not be understood;

        5xx: Execution reject -- the transaction received could not be executed;


MEGACOP Transaction Response Codes are extensible.   MEGACOP applica-
tions are not required to understand the meaning of all registered
response codes, though such understanding is obviously desirable. How-
ever, applications MUST understand the class of any response code, as
indicated by the first digit, and treat any unrecognized response code
as being equivalent to the x00 response code of that class.

5.6.1.  Transaction Response Success Codes

     Success  =  "200"  ;  The requested transaction was executed nor-
     mally

5.6.2.  Transaction Response Reject Codes

        Protocol-Reject  =  "400"  ;  Bad Request
        Protocol-Reject  =  "400"  ;  Bad Request
                /   "401"  ;  Unauthorized
                /   "411"  ;  Length Required
                /   "415"  ;  Incorrect identifier
                /   "416"  ;  The transaction refers to an unknown ContextId
                /   "418"  ;  Unsupported or unknown Package
                /   "422"  ;  No such Event or signal
                /   "423"  ;  Unknown action or illegal combination of actions
                /   "425"  ;  Unknown TerminationID
                /   "427"  ;  Missing RemoteTerminationDescriptor
                /   "484"  ;  Action Incomplete
                /   "485"  ;  Action Ambiguous

        Execution-Reject  =  "500"  ;  Internal Gateway Error
                /   "501"  ;  Not Implemented
                /   "502"  ;  Not ready.



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                /   "503"  ;  Service Unavailable
                /   "504"  ;  Gateway Time-out
                /   "505"  ;  MEGACOP Version not supported
                /   "509"  ;  Resource Conflict
                /   "510"  ;  Insufficient resources
                /   "512"  ;  Gateway unequipped to detect requested Event
                /   "513"  ;  Gateway unequipped to generate requested Signals
                /   "514"  ;  Gateway cannot send the specified announcement
                /   "515"  ;  Unsupported Media Type
                /   "517"  ;  Unsupported or invalid mode
                /   "519"  ;  Gateway does not have a digit map
                /   "520"  ;  Termination is "ServiceChangeing"
                /   "526"  ;  Insufficient bandwidth
                /   "581"  ;  Does Not Exist


6.  Transport

The transport mechanism for MEGACOP has not been chosen.  It is likely
that TCP will be an option.  If the SIGTRAN transport mechanism is suit-
able for MEGACO, that may be specified.  It may be necessary to specify
a transport protocol in this specification.  Either the SIGTRAN mechan-
ism or a MEGACO specified mechanism will be optional on the MG and
required on the MGC.

6.1.  Transport capabilities, and relationship to Transport Layer

Requirements for transport of the MEGACO protocol include:

1)   Reliable delivery of commands/responses.


2)   Ordered delivery of commands/responses to a particular "control
     stream", this implies ordered delivery of commands to/from  a par-
     ticular Termination or Context, but not necessarily ordered
     across Terminations or Contexts.

3)   Limited maximum time to deliver commands.

4)   Rapid detection of failure in a control stream.

5)   Ability to achieve very high fanout from MGC to MGs.

6)   Ability to handle multiple MGCs controlling individual MGs in a
     distributed system and vice versa.  However this must be optional
     so that smaller/simpler systems can be efficiently implemented.

7)   Ability for the application to initiate flushing of messages



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     successfully sent through the transport, for example to back off
     for failover handling.

Since transport needs are the same in all application states and
independent of what particular commands are being sent, it is logical to
think of the reliable transport as a separate layer, as shown below.
However, there is no accepted IETF protocol which focuses on the needs
of real time control as is needed by the MEGACO protocol. Therefore, the
mechanisms to provide the required characteristics of the reliable tran-
sport should be directly included in the MEGACO protocol layer. However,
It might be desirable to standardize the transport interface (marked in
the figure by - . - . - ). This is discussed in section [4.z.z].

                  MEGACO Protocol layer:
                    Gateway control  |  Termination-related signalling
                   - . - . - . - . - . - . - . - . - . - . - . - . -
                                Reliable transport
                   -------------------------------------------------
                                      UDP
                   -------------------------------------------------
                                      IP
                   -------------------------------------------------
                             Ethernet, ATM, SONET, ...


Any message goes between one MG and one MGC.  This has implications on
MG or MGC "farms".

7.  Event Packages and Termination Classes

Termination Classes are defined by:

*    A plain text description of the purpose of the Termination Class,

*    An SDP profile describing which SDP attributes are used in the the
     Local and Remote Termination descriptors,

*    A default value for the Local and Remote Termination descriptions,

*    The definition of statistics that can be collected on the Termina-
     tion,

*    A list of Events and Signals that are defined for the Termination,

The Events and Signals are grouped in "Event Packages", some of which
may apply to different Termination Classes. The list of Events and Sig-
nals applicable for a Termination Class must thus be defined by the list
of applicable Event Packages.



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In this section, we will describe the most common Event Packages, and
then the most common Termination Classes. More Packages and Classes can
be defined in additional documents.

7.1.  Basic Event Packages

The list of basic Event Packages includes the following:

               _________________________________________
              | Package                      |   name  |
              |______________________________|_________|
              | Generic Media Package        |   G     |
              | DTMF Package                 |   D     |
              | MF Package                   |   M     |
              | Trunk Package                |   T     |
              | Line Package                 |   L     |
              | Handset Package              |   H     |
              | RTP Package                  |   R     |
              | Network Access Server Package|   N     |
              | Announcement Server Package  |   A     |
              | Script Package               |   Script|
              |______________________________|_________|


In the tables of Events for each Package, there are five columns:
     Symbol: the unique symbol used for the Event
     Definition: a short description of the Event

     R:   an x appears in this column is the Event can be Requested by
          the call agent.

     S:   if nothing appears in this column for an Event, then the Event
          cannot be signaled on command by the call agent. Otherwise,
          the following symbols identify the type of Event:

          OO   On/Off Signal.  The Signal is turned on until commanded
               by the call agent to turn it off, and vice versa.

          TO   Timeout Signal.  The Signal lasts for a given duration
               unless it is superseded by a new Signal.

          BR   Brief Signal.  The Event has a short, known duration.

          Duration: specifies the duration of TO Signals.

7.1.1.  Generic Media Event Package

Package Name: G



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The generic media Package group the Events and Signals that can be
observed on several types of Terminations, such as trunking gateways,
access gateways or residential gateways.

 ______________________________________________________________________
| Symbol   |   Definition                |   R |   S      Duration    |
|__________|_____________________________|_____|______________________|
| mt       |   Modem detected            |   x |                      |
| fn       |   CalliNg Fax tone detected |   x |                      |
| fd       |   CalleD Fax tone detected  |   x |                      |
| ld       |   Long duration connection  |   x |                      |
| pat(###) |   Pattern ### detected      |   x |   OO                 |
| rt       |   Ringback tone             |     |   TO                 |
| rbk(###) |   ring back on connection   |     |   TO     180 seconds |
| cf       |   Confirm tone              |     |   BR                 |
| cg       |   Network Congestion tone   |     |   TO                 |
| it       |   Intercept tone            |     |   OO                 |
| pt       |   Preemption tone           |     |   OO                 |
| of       |   report failure            |   x |                      |
|__________|_____________________________|_____|______________________|

The Signals are defined as follow:

     The pattern definition can be used for specific algorithms such as
     answering machine detection, tone detection, and the like.

Ring back tone (rt)
     an Audible Ring Tone, a combination of two AC tones with frequen-
     cies of 440 and 480 Hertz and levels of -19 dBm each, to give a
     combined level of -16 dBm.  The cadence for Audible Ring Tone is 2
     seconds on followed by 4 seconds off. See GR- 506-CORE - LSSGR:
     SIGNALING, Section 17.2.5.

Ring back on connection
     A ring back tone, applied to the connection whose identifier is
     passed as a property.

The "long duration connection" is detected when a connection has been
established for more than 1 hour.

7.1.2.  DTMF Event Package

Package name: D








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    _______________________________________________________________
   | Symbol |   Definition              |   R |   S      Duration |
   |________|___________________________|_____|___________________|
   | 0      |   DTMF 0                  |   x |   BR              |
   | 1      |   DTMF 1                  |   x |   BR              |
   | 2      |   DTMF 2                  |   x |   BR              |
   | 3      |   DTMF 3                  |   x |   BR              |
   | 4      |   DTMF 4                  |   x |   BR              |
   | 5      |   DTMF 5                  |   x |   BR              |
   | 6      |   DTMF 6                  |   x |   BR              |
   | 7      |   DTMF 7                  |   x |   BR              |
   | 8      |   DTMF 8                  |   x |   BR              |
   | 9      |   DTMF 9                  |   x |   BR              |
   | #      |   DTMF #                  |   x |   BR              |
   | *      |   DTMF *                  |   x |   BR              |
   | A      |   DTMF A                  |   x |   BR              |
   | B      |   DTMF B                  |   x |   BR              |
   | C      |   DTMF C                  |   x |   BR              |
   | D      |   DTMF D                  |   x |   BR              |
   | L      |   long duration indicator |   x |          2 seconds|
   | X      |   Wildcard, match         |   x |                   |
   |        |   any digit 0-9           |     |                   |
   | T      |   Interdigit timer        |   x |          4 seconds|
   | of     |   report failure          |   x |                   |
   |________|___________________________|_____|___________________|


The "interdigit timer" occurs when a long delay is observed after the
end of a digit detection.  The Event can only be observed if the Termi-
nation is trying to acquire digits.  Note that the definition of this
timer requires further study.  In fact, the timer should take two dif-
ferent values, depending of the digit map and the digit string:

-    If the gateway can determine that at least one more digit is
     requested for the digit string to match any of the allowed patterns
     in the digit map, then the timer value should be set to a long
     duration, such as 16 seconds.

-    If the digit map specifies that a variable number of additional
     digits may be needed (the "." indication at the end of a string),
     then the timer value should be set to a medium duration, such as 8
     seconds.

-    In some rare cases, such as optional additional digits, the timer
     should be set to a short duration, 4 seconds.  The current digit
     map syntax does not allow for a distinction between the "medium"
     and "short" timer conditions, which implies that, in the current
     version, there is no way to request a short timer.



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The "long duration indicator" is observed when a DTMF signal is produced
for a duration larger than two seconds.  In this case, the gateway will
detect two successive Events: first, when the Signal has been recog-
nized, the DTMF signal, and then, 2 seconds later, the long duration
signal.














































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7.1.3.  MF Event Package

Package Name: M

        ________________________________________________________
       | Symbol |   Definition       |   R |   S      Duration |
       |________|____________________|_____|___________________|
       | 0      |   MF 0             |   x |   BR              |
       | 1      |   MF 1             |   x |   BR              |
       | 2      |   MF 2             |   x |   BR              |
       | 3      |   MF 3             |   x |   BR              |
       | 4      |   MF 4             |   x |   BR              |
       | 5      |   MF 5             |   x |   BR              |
       | 6      |   MF 6             |   x |   BR              |
       | 7      |   MF 7             |   x |   BR              |
       | 8      |   MF 8             |   x |   BR              |
       | 9      |   MF 9             |   x |   BR              |
       | X      |   Wildcard, match  |   x |                   |
       |        |   any digit 0-9    |     |                   |
       | T      |   Interdigit timer |   x |          4 seconds|
       | K0     |   MF K0 or KP      |   x |   BR              |
       | K1     |   MF K1            |   x |   BR              |
       | K2     |   MF K2            |   x |   BR              |
       | S0     |   MF S0 or ST      |   x |   BR              |
       | S1     |   MF S1            |   x |   BR              |
       | S2     |   MF S2            |   x |   BR              |
       | S3     |   MF S3            |   x |   BR              |
       | wk     |   Wink             |   x |   BR              |
       | wko    |   Wink off         |   x |   BR              |
       | is     |   Incoming seizure |   x |   OO              |
       | rs     |   Return seizure   |   x |   OO              |
       | us     |   Unseize circuit  |   x |   OO              |
       | of     |   report failure   |   x |                   |
       |________|____________________|_____|___________________|


The definition of the MF Package Events is as follow:

Wink
     A transition from unseized to seized to unseized trunk states
     within a specified period.  Typical seizure period is 100-350
     msec.)

Incoming seizure
     Incoming indication of call attempt.

Return seizure:
     Seizure in response to outgoing seizure.



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Unseize circuit:
     Unseizure of a circuit at the end of a call.

Wink off:
     A Signal used in operator services trunks.  A transition from
     seized to unseized to seized trunk states within a specified period
     of 100-350 ms. (To be checked)

7.1.4.  Trunk Event Package

Package Name: T

 _____________________________________________________________________
| Symbol |   Definition                   |   R |   S      Duration  |
|________|________________________________|_____|____________________|
| co1    |   Continuity tone (single tone,|   x |   OO               |
|        |   or return tone)              |     |                    |
| co2    |   Continuity test (go tone,    |   x |   OO               |
|        |  in dual tone procedures)      |     |                    |
| lb     |   Loopback                     |     |   OO               |
| om     |   Old Milliwatt Tone (1000 Hz) |   x |   OO               |
| nm     |   New Milliwatt Tone (1004 Hz) |   x |   OO               |
| tl     |   Test Line                    |   x |   OO               |
| zz     |   No circuit                   |   x |   OO               |
| as     |   Answer Supervision           |   x |   OO               |
| ro     |   Reorder Tone                 |   x |   TO     30 seconds|
| of     |   report failure               |   x |                    |
|________|________________________________|_____|____________________|


The definition of the trunk Package Signal Events is as follow:

Continuity Tone (co1):
     A tone at 2010 + or - 30 Hz.

Continuity Test (co2):
     A tone at the 1780 + or - 30 Hz.

Milliwatt Tones:
     Old Milliwatt Tone (1000 Hz), New Milliwatt Tone (1004 Hz)

Line Test:
     105 Test Line test progress tone (2225 Hz + or - 25 Hz at -10 dBm0
     + or -- 0.5dB).

No circuit:
     (that annoying tri-tone, low to high)




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Answer Supervision:

Reorder Tone:
     Reorder tone is a combination of two AC tones with frequencies of
     480 and 620 Hertz and levels of -24 dBm each, to give a combined
     level of -21 dBm.  The cadence for Station Busy Tone is 0.25
     seconds on followed by 0.25 seconds off, repeating continuously.
     See GR-506-CORE - LSSGR: SIGNALING, Section 17.2.7.

The continuity tones are used when the call agent wants to initiate a
continuity test. There are two types of tests, single tone and dual
tone. The Call agent is expected to know, through provisioning informa-
tion, which test should be applied to a given Termination. For example,
the controller that wants to initiate a single frequency test will send
to the gateway a command of the form:

        RQNT 1234 epx-t1/17@tgw2.example.net
        X: AB123FE0
        S: co1
        R: co1

If it wanted instead to initiate a dual-tone test, it would send the
command:

        RQNT 1234 epx-t1/17@tgw2.example.net
        X: AB123FE0
        S: co2
        R: co1

The gateway would send the requested signal, and in both cases would
look for the return of the 2010 Hz tone (co1).  When it detects that
tone, it must send the corresponding  notification.

The tones are of type OO: the gateway must keep sending them until it
receives a new notification request.

7.1.5.  Line Event Package

Package Name: L












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__________________________________________________________________________
|Symbol       |   Definition                 |   R |   S      Duration   |
|_____________|______________________________|_____|_____________________|
|adsi(string) |   adsi display               |     |   BR                |
|vmwi         |   visual message             |     |   TO                |
|             |   waiting indicator          |     |                     |
|hd           |   Off hook transition        |   x |                     |
|hu           |   On hook transition         |   x |                     |
|hf           |   Flash hook                 |   x |                     |
|aw           |   Answer tone                |   x |   OO                |
|bz           |   Busy tone                  |     |   TO     30 seconds |
|ci(string)   |   Caller-id                  |     |   BR                |
|wt           |   Call Waiting tone          |     |   TO     30 seconds |
|dl           |   Dial tone                  |     |   TO     16 seconds |
|mwi          |   Message waiting ind.       |     |   TO     16 seconds |
|nbz          |   Network busy               |   x |   OO                |
|             |   (fast cycle busy)          |     |                     |
|rg           |   Ringing                    |     |   TO     180 seconds|
|r0, r1, r2,  |  Distinctive ringing         |     |   TO     180 seconds|
|r3, r4, r5,  |                              |     |                     |
|r6 or r7     |                              |     |                     |
|rs           |   Ringsplash                 |     |   BR                |
|p            |   Prompt tone                |   x |   BR                |
|e            |   Error tone                 |   x |   BR                |
|sdl          |   Stutter dialtone           |     |   TO     16 seconds |
|v            |   Alerting Tone              |     |   OO                |
|y            |   Recorder Warning Tone      |     |   OO                |
|sit          |   SIT tone                   |     |                     |
|z            |   Calling Card Service Tone  |     |   OO                |
|oc           |   Report on completion       |   x |                     |
|ot           |   Off hook warning tone      |     |   TO     indefinite |
|s(###)       |   Distinctive tone pattern   |   x |   BR                |
|of           |   report failure             |   x |                     |
|_____________|______________________________|_____|_____________________|


The definition of the tones is as follow:

Dial tone:
     A combined 350 + 440 Hz tone.

Visual Message Waiting Indicator
     The transmission of the VMWI messages must conform to the require-
     ments in Section 2.3.2, "On-hook Data Transmission Not Associated
     with Ringing" in TR-H- 000030 and the CPE guidelines in SR-TSV-
     002476. VMWI messages must only be sent from the SPCS when the line
     is idle. If new messages arrive while the line is busy, the VMWI
     indicator message must be delayed until the line goes back to the



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     idle state. The CA should periodically refresh the CPE's visual
     indicator. See TR-NWT-001401 - Visual Message Waiting Indicator
     Generic Requirements; and GR- 30-CORE - Voiceband Data Transmission
     Interface.

Message waiting Indicator
     See GR-506-CORE, 17.2.3.

Alerting Tone:
     a 440 Hz Tone of 2 second duration followed by 1/2 second of tone
     every 10 seconds.

Rig splash
     Ringsplash, also known as "Reminder ring" is a burst of ringing
     that may be applied to the physical forwarding line (when idle) to
     indicate that a call has been forwarded and to remind the user that
     a CF subfeature is active.  In the US, it is defined to be a 0.5(-
     0,+0.1) second burst of power ringing. See TR- TSY-000586 - Call
     Forwarding Subfeatures.

Call waiting tone
     Call Waiting tone is defined in GR-506-CORE, 14.2. Call Waiting
     feature is defined in TR-TSY-000571. By defining "wt" as a TO Sig-
     nal you are really defining the feature which seems wrong to me
     (given the spirit of MGCP), hence the definition of "wt" as a BR
     Signal in ECS, per GR-506-CORE. Also, it turns out that there is
     actually four different call waiting tone patterns (see GR-506-
     CORE, 14.2) so we should really have wt1, wt2, wt3, wt4, or some
     parameterization.

Recorder Warning Tone:
     1400 Hz of Tone of 0.5 second duration every 15 seconds.

SIT tone:
     used for indicating a line is out of service.

Calling Card Service Tone:
     60 ms of 941 + 1477 Hz and 940 ms of 350 + 440 Hz (dial tone),
     decaying exponentially with a time constant of 200 ms.

Distinctive tone pattern:
     where ### is any number between 000 and 999, inclusive.  Can be
     used for distinctive ringing, customized dial tone, etc.

Report on completion
     The report on completion Event is detected when the gateway was
     asked to perform one or several Signals of type TO on the Termina-
     tion, and when these Signals were completed without being stopped



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     by the detection of a requested Event such as off-hook transition
     or dialed digit.  The completion report may carry as property the
     name of the Signal that came to the end of its live time, as in:

             O: L/oc(L/dl)


Ring back on connection
     A ring back tone, applied to the connection whose identifier is
     passed as a property.

We should note that many of these definitions vary from country to coun-
try.  The frequencies listed above are the one in use in North America.
There is a need to accommodate different tone sets in different coun-
tries, and there is still an ongoing debate on the best way to meet that
requirement:

*    One solution is to define different Event Packages specifying for
     example the German dial-tone as "L-DE/DL".

*    Another solution is to use a management interface to specify on an
     end-point basis which frequency shall be associated to what tone.





























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7.1.6.  Handset emulation Event Package

Package Name: H

__________________________________________________________________________
|Symbol       |   Definition                 |   R |   S      Duration   |
|_____________|______________________________|_____|_____________________|
|adsi(string) |   adsi display               |   x |   BR                |
|tdd          |                              |     |                     |
|vmwi         |                              |     |                     |
|hd           |   Off hook transition        |   x |   OO                |
|hu           |   On hook transition         |   x |   OO                |
|hf           |   Flash hook                 |   x |   BR                |
|aw           |   Answer tone                |   x |   OO                |
|bz           |   Busy tone                  |   x |   OO                |
|wt           |   Call Waiting tone          |   x |   TO     30 seconds |
|dl           |   Dial tone (350 + 440 Hz)   |   x |   TO     120 seconds|
|nbz          |   Network busy               |   x |   OO                |
|             |   (fast cycle busy)          |     |                     |
|rg           |   Ringing                    |   x |   TO     30 seconds |
|r0, r1, r2,  |  Distinctive ringing         |   x |   TO     30 seconds |
|r3, r4, r5,  |                              |     |                     |
|r6 or r7     |                              |     |                     |
|p            |   Prompt tone                |   x |   BR                |
|e            |   Error tone                 |   x |   BR                |
|sdl          |   Stutter dialtone           |   x |   TO     16 seconds |
|v            |   Alerting Tone              |   x |   OO                |
|y            |   Recorder Warning Tone      |   x |   OO                |
|t            |   SIT tone                   |   x |                     |
|z            |   Calling Card Service Tone  |   x |   OO                |
|oc           |   Report on completion       |   x |                     |
|ot           |   Off hook warning tone      |   x |   OO                |
|s(###)       |   Distinctive tone pattern   |   x |   BR                |
|of           |   report failure             |   x |                     |
|_____________|______________________________|_____|_____________________|


The handset emulation Package is an extension of the line Package, to be
used when the gateway is capable of emulating a handset.  The difference
with the line Package is that Events such as "off hook" can be signalled
as well as detected.










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7.1.7.  RTP Event Package

Package Name: R

   _________________________________________________________________
  | Symbol  |   Definition                 |   R |   S     Duration|
  |_________|______________________________|_____|_________________|
  | UC      |   Used codec changed         |   x |                 |
  | SR(###) |   Sampling rate changed      |   x |                 |
  | JI(###) |   Jitter buffer size changed |   x |                 |
  | PL(###) |   Packet loss exceeded       |   x |                 |
  | qa      |   Quality alert              |   x |                 |
  | of      |   report failure             |   x |                 |
  |_________|______________________________|_____|_________________|


Codec Changed:
     Codec changed to hexadecimal codec number enclosed in parenthesis,
     as in UC(15), to indicate the codec was changed to PCM mu-law.
     Codec Numbers are specified in RFC 1890, or in a new definition of
     the audio profiles for RTP that replaces this RFC.  Some implemen-
     tations of media gateways may not allow the codec to be changed
     upon command from the call agent.  codec changed to codec hexade-
     cimal ##.

Sampling Rate Changed:
     Sampling rate changed to decimal number in milliseconds enclosed in
     parenthesis, as in SR(20), to indicate the sampling rate was
     changed to 20 milliseconds.  Some implementations of media gateways
     may not allow the sampling rate to be changed upon command from a
     call agent.

Jitter Buffer Size Changed:
     When the media gateway has the ability to automatically adjust the
     depth of the jitter buffer for received RTP streams, it is useful
     for the media gateway controller to receive notification that the
     media gateway has automatically increased its jitter buffer size to
     accommodate increased or decreased variability in network latency.
     The syntax for requesting notification is "JI", which tells the
     media gateway that the controller wants notification of any jitter
     buffer size changes.  The syntax for notification from the media
     gateway to the controller is "JI(####)", where the #### is the new
     size of the jitter buffer, in milliseconds.

Packet Loss Exceeded:
     Packet loss rate exceed the threshold of the specified decimal
     number of packets per 100,000 packets, where the packet loss number
     is contained in parenthesis.  For example, PL(10) indicates packets



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     are being dropped at a rate of 1 in 10,000 packets.

Quality alert
     The packet loss rate or the combination of delay and jitter exceed
     a specified quality threshold.

7.1.8.  Network Access Server Event Package

Package Name: N

      ____________________________________________________________
     | Symbol |   Definition             |   R |   S     Duration|
     |________|__________________________|_____|_________________|
     | pa     |  Packet arrival          |  x  |                 |
     | cbk    |  Call back request       |  x  |                 |
     | cl     |  Carrier lost            |  x  |                 |
     | au     |   Authorization succeeded|  x  |                 |
     | ax     |   Authorization denied   |  x  |                 |
     | of     |   Report failure         |  x  |                 |
     |________|__________________________|_____|_________________|


The packet arrival Event is used to notify that at least one packet was
recently sent to an Internet address that is observed by an Termination.
The Event report includes the Internet address, in standard ASCII encod-
ing, between parenthesis:

        O: pa(192.96.41.1)


The call back Event is used to notify that a call back has been
requested during the initial phase of a data connection. The Event
report includes the identification of the user that should be called
back, between parenthesis:

        O: cbk(user25)















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7.1.9.  Announcement Server Event Package

Package Name: A

  ___________________________________________________________________
 | Symbol         |   Definition           |   R |   S      Duration|
 |________________|________________________|_____|__________________|
 | ann(url,parms) |   Play an announcement |     |   TO     variable|
 | oc             |   Report on completion |   x |                  |
 | of             |   Report failure       |   x |                  |
 |________________|________________________|_____|__________________|

The announcement action is qualified by an URL name and by a set of ini-
tial properties as in for example:

        S: ann(http://scripts.example.net/all-lines-busy.au)

The "operation complete" Event must be detected when the announcement is
played out. If the announcement cannot be played out, an operation
failure Event can be returned.  The failure may be explained by a com-
mentary, as in:

        O: A/of(file not found)




























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7.1.10.  Script Event Package

Package Name: Script

     ______________________________________________________________
    | Symbol    |   Definition           |   R |   S  |   Duration|
    |___________|________________________|_____|______|___________|
    | java(url) |   Load a java script   |     |   TO |   variable|
    | perl(url) |   Load a perl script   |     |   TO |   variable|
    | tcl(url)  |   Load a TCL script    |     |   TO |   variable|
    | xml(url)  |   Load an XML script   |     |   TO |   variable|
    | oc        |   Report on completion |   x |      |           |
    | of        |   Report failure       |   x |      |           |
    |___________|________________________|_____|______|___________|

The "language" action define is qualified by an URL name and by a set of
initial properties as in for example:

        S: script/java(http://scripts.example.net/credit-card.java,long,1234)


The current definition defines keywords for the most common languages.
More languages may be defined in further version of this documents.  For
each language, an API specification must describe how the scripts can
issue local "notificationRequest" commands, and receive the correspond-
ing notifications.

The script produces an output which consists of one or several text
string, separated by commas.  The text string are reported as a commen-
tary in the report on completion, as in for example:

        O: script/oc(21223456794567,9738234567)

The failure report may also return a string, as in:

        O: script/oc(21223456794567,9738234567)

The definition of the script environment and the specific actions in
that environment are for further study.












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7.2.  Basic Termination Classes

We define the following basic Termination types and profiles:

*    DS0 Termination,

*    Analog Termination,

*    RTP Termination,

*    ATM Termination,

*    Network Access Termination.

Editors' note: These are only the most basic Termination types. There is
an obvious need to also define digital multiplexes (T1, E1, T3, E3) and
the Events that they support.

7.2.1.  DS0 Terminations

DS0 Terminations are digital circuits, providing a 64kbits (8bit times 8
KHz) service. Such Terminations are commonly used for interoffice
trunks.

DS0 Terminations are always described in a symmetric fashion.  The
RemoteTerminationDescriptor parameter is never used.

The LocalTerminationDescriptor may be used to specify the encoding of
the media.  This parameter is described using SDP, with the following
conventions:

*    The connection data line is not used.  A placeholder (c=LOCAL) can
     be used if this is required for compliance with the SDP syntax.

*    The "m=audio" property must specify a port number, which must
     always be set to 0, the type of protocol, always set to the keyword
     DS0, and the type of encoding, using the same conventions used for
     RTP (RTP payload numbers.) The type of encoding should normally be
     set to 0 (PCM, mu law) or to 8 (PCM, A law).

*    The "a=echo" attribute must specify whether the gateway performs
     echo cancellation. The property can have two values, "a:echo:on"
     (when the echo cancellation is requested) and "a:echo:off" (when it
     is turned off.)

*    The gain control attribute, encoded as the keyword "gc", followed
     by a colon a value which can be either the keyword "auto" or a
     decimal number (positive or negative) representing the number of



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     decibels of gain.

An example of specification could be:

        v=0
        c=LOCAL
        m=audio 0 DS0 0
        a=echo:on


The default configuration option is to use the mu-law encoding, with
gain control set to auto, and to apply echo cancellation.  (We could
define a variant of the DS0 Class which would, by default, use A-law
encoding.)

Gateways are expected to be able to collect the following statistics on
Terminations of the DS0 Class:

     Number of octets sent, number of octets received
     The number of octet sent or received is equal to the duration of
     the Termination, in seconds, multiplied by the sampling frequency,
     8000 Hz.

Terminations of the DS0 Class are expected to provide the following sup-
port for Event Packages:

_______________________________________________________________________
|Package               |   name   |   support in DS0 Class            |
|______________________|__________|___________________________________|
|Generic Media Package |   G      |   Mandatory                       |
|Trunk Package         |   T      |   Mandatory                       |
|DTMF Package          |   D      |   Optional (for credit cards, etc)|
|MF Package            |   M      |   Optional (for MF trunks)        |
|Announcement          |   A      |   Optional (when gateway          |
|Server Package        |          |   can play announcement on DS0)   |
|Script Package        |   Script |   Optional                        |
|______________________|__________|___________________________________|


7.2.2.  Analog Terminations

Analog terminations are analog circuits, typically connected through an
RJ11 interface.  Such Terminations are commonly found in residential
gateways.

Analog Terminations are always described in a symmetric fashion.  The
RemoteTerminationDescriptor parameter is never used.




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The LocalTerminationDescriptor may be used to specify the encoding of
the media.  This parameter is described using SDP, with the following
conventions:

*    The connection data line is not used.  A placeholder (c=LOCAL) can
     be used if this is required for compliance with the SDP syntax.

*    The "m=audio" property is only used for conformance with the SDP
     syntax.  It is set to a conventional value, specifying a null port,
     an ANALOG type and a null type of encoding.

*    The "a=echo" attribute must specify whether the gateway performs
     echo cancellation. The property can have two values, "a:echo:on"
     (when the echo cancellation is requested) and "a:echo:off" (when it
     is turned off.)

*    The gain control attribute, encoded as the keyword "gc", followed
     by a colon a value which can be either the keyword "auto" or a
     decimal number (positive or negative) representing the number of
     decibels of gain.

An example of specification could be:

        v=0
        c=LOCAL
        m=audio 0 ANALOG 0
        a=echo:on


The default configuration option is to apply echo cancellation, and to
have gain control set to auto.

Gateways are expected to be able to collect the following statistics on
Terminations of the analog Class:

     Number of octets sent, number of octets received
     The number of octet sent or received is equal to the duration of
     the Termination, in seconds, multiplied by the sampling frequency,
     8000 Hz.

Terminations of the analog Class are expected to provide the following
support for Event Packages:









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  ____________________________________________________________________
 | Package               |   name   |   support in analog Class      |
 |_______________________|__________|________________________________|
 | Generic Media Package |   G      |   Mandatory                    |
 | DTMF Package          |   D      |   Mandatory                    |
 | Line Package          |   L      |   Mandatory                    |
 | Handset Package       |   H      |   Optional (when gateway       |
 |                       |          |   can set outgoing calls on    |
 |                       |          |   the analog Termination)      |
 | Announcement          |   A      |   Optional (when gateway       |
 | Server Package        |          |   can play announcements on the|
 |                       |          |   Termination)                 |
 | Script Package        |   Script |   Optional                     |
 |_______________________|__________|________________________________|


7.2.3.  RTP Audio Terminations

RTP Terminations are use to describe the local Termination of packet
connections established through the RTP, UDP and IP protocols. The RTP
Audio Termination Class is applied when the RTP Terminations convey an
audio media. (Other Termination Classes may be used for other media,
such as video.)

The encoding of the media in point to point RTP Terminations is
described by two sets of properties, the LocalTerminationDescriptor and
the RemoteTerminationDescriptor. Both are described using SDP, with the
following conventions:

*    The IP address of the remote gateway (in commands) or of the local
     gateway (in responses), or multicast address of the audio confer-
     ence, encoded as an SDP "connection data" parameter. This parameter
     specifies the IP address that must be used to exchange RTP packets.

*    Media description field (m) specifying the audio media, the tran-
     sport port used for receiving RTP packets by the remote gateway
     (commands) or by the local gateway (responses) , the RTP/AVP tran-
     sport, and the list of formats that the gateway must accept. This
     list should normally always include the code 0 (reserved for G.711,
     mu law).

*    Optionally, RTPMAP attributes that define the encoding of dynamic
     audio formats,

*    Optionally, a packetization period (packet time) attribute (Ptime)
     defining the duration of the packet,

*    Optionally, an encryption key attribute ("k"), specifying the



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     encryption and the key for the RTP packets, as defined in SDP.

*    Optionally, an attribute defining the type of connection (sendonly,
     recvonly, sendrecv, inactive). Note that this attribute does not
     have a direct relation with the "Mode" property of the Termination.
     In fact, the SDP type of connection will most of the time be set to
     "sendrecv", regardless of the value used for the Termination.
     Other values will only be used rarely, for example in the case of
     information or announcement servers that need to establish one way
     connections.

An example of specification could be:

        v=0
        c=IN IP4 128.96.41.1
        m=audio 3456 RTP/AVP 0 96
        a=rtpmap:96 G726-32/8000


The default configuration for the LocalTerminationDescriptor is to use
one of the IP addresses of the gateway, to select a UDP port for RTP,
and to use the PCM mu-law algorithm.

Gateways are expected to be able to collect the following statistics on
Terminations of the RTP Class:

     Number of packets sent:
     The total number of RTP data packets transmitted by the sender
     since starting transmission on this connection. The count is not
     reset if the sender changes its synchronization source identifier
     (SSRC, as defined in RTP), for example as a result of a Modify com-
     mand. The value is zero if the connection was set in "receive only"
     mode.

     Number of octets sent:
     The total number of payload octets (i.e., not including header or
     padding) transmitted in RTP data packets by the sender since start-
     ing transmission on this connection. The count is not reset if the
     sender changes its SSRC identifier, for example as a result of a
     Modify command. The value is zero if the connection was set in
     "receive only" mode.

     Number of packets received:
     The total number of RTP data packets received by the sender since
     starting reception on this connection. The count includes packets
     received from different SSRC, if the sender used several values.
     The value is zero if the connection was set in "send only" mode.




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     Number of octets received:
     The total number of payload octets (i.e., not including header or
     padding) transmitted in RTP data packets by the sender since start-
     ing transmission on this connection. The count includes packets
     received from different SSRC, if the sender used several values.
     The value is zero if the connection was set in "send only" mode.

     Number of packets lost:
     The total number of RTP data packets that have been lost since the
     beginning of reception. This number is defined to be the number of
     packets expected less the number of packets actually received,
     where the number of packets received includes any which are late or
     duplicates. The count includes packets received from different
     SSRC, if the sender used several values. Thus packets that arrive
     late are not counted as lost, and the loss may be negative if there
     are duplicates. The count includes packets received from different
     SSRC, if the sender used several values. The number of packets
     expected is defined to be the extended last sequence number
     received, as defined next, less the initial sequence number
     received. The count includes packets received from different SSRC,
     if the sender used several values. The value is zero if the connec-
     tion was set in "send only" mode. This property is omitted if the
     connection was set in "data" mode.

     Interarrival jitter:
     An estimate of the statistical variance of the RTP data packet
     interarrival time measured in milliseconds and expressed as an
     unsigned integer. The interarrival jitter J is defined to be the
     mean deviation (smoothed absolute value) of the difference D in
     packet spacing at the receiver compared to the sender for a pair of
     packets. Detailed computation algorithms are found in RFC 1889. The
     count includes packets received from different SSRC, if the sender
     used several values. The value is zero if the connection was set in
     "send only" mode. This property is omitted if the connection was
     set in "data" mode.

     Average transmission delay:
     An estimate of the network latency, expressed in milliseconds. This
     is the average value of the difference between the NTP timestamp
     indicated by the senders of the RTCP messages and the NTP timestamp
     of the receivers, measured when this messages are received. The
     average is obtained by summing all the estimates, then dividing by
     the number of RTCP messages that have been received. This property
     is omitted if the connection was set in "data" mode.
     When the MG's clock is not synchronized by NTP, the latency value
     can be computed as one half of the round trip delay, as measured
     through RTCP.
     When the MG cannot compute the one way delay or the round trip



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     delay, the property conveys a null value.

For a detailed definition of these variables, refer to RFC 1889.
















































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Terminations of the RTP Class are expected to provide the following sup-
port for Event Packages:

     _____________________________________________________________
    | Package               |   name   |   support in RTP Class  |
    |_______________________|__________|_________________________|
    | RTP Package           |   R      |   Mandatory             |
    | Generic Media Package |   G      |   Mandatory             |
    | DTMF Package          |   D      |   Optional (e.g. in     |
    |                       |          |   IVR units)            |
    | Announcement          |   A      |   Optional (when gateway|
    | Server Package        |          |   can play announcement |
    |                       |          |   on RTP)               |
    | Script Package        |   Script |   Optional              |
    |_______________________|__________|_________________________|


7.2.4.  ATM audio Terminations

ATM Terminations are use to describe the local Termination of packet
connections established over ATM networks. The RTP Audio Termination
Class is applied when the RTP Terminations convey an audio media. (Other
Termination Classes may be used for other media, such as video.)

The encoding of the media in point to point RTP Terminations is
described by two sets of properties, the LocalTerminationDescriptor and
the RemoteTerminationDescriptor. Both are described using SDP, with the
following conventions:

*    The "c=" property of SDP to specifies an address in the ATM family,
     the ATM addressing variant (NSAP, UNI, E.164) and the ATM address.

*    The "m=audio" property must specify the audio encoding and, if
     needed, the VPI and VCI.

*    Additional attributes properties (a=) will be used to specify the
     ATM coding variants, such as the type of adaptation layer and the
     error correction or loss compensation algorithms.

An example of SDP payload for an ATM connection could be:

        v=0
        c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.fe
        m=audio 5/1002 ATM/AVP G.711u
        a=connection_type:AAL2


The default configuration for the LocalTerminationDescriptor is to use



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one of the ATM addresses of the gateway, to select a VPI and a VCI, and
to use the PCM mu-law algorithm.

Gateways are expected to be able to collect the following statistics on
Terminations of the ATM Class:

     Number of packets sent:
     The total number of ATM cells transmitted since starting transmis-
     sion on this connection.

Number of octets sent:
     The total number of payload octets transmitted in ATM cells.

Number of packets received:
     The total number of ATM cells received since starting reception on
     this connection.

Number of octets received:
     The total number of payload octets received in ATM cells.

Number of packets lost:
     Should be determined as the number of cells lost, or set to zero if
     the adaptation layer does not enable the MG to assess losses.

Interarrival jitter:
     The interarrival jitter between ATM cells.

Average transmission delay:
     The MG may not be able to assess this property over an ATM network.
     It could simply report a null value.





















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Terminations of the ATM Class are expected to provide the following sup-
port for Event Packages:

     _____________________________________________________________
    | Package               |   name   |   support in ATM Class  |
    |_______________________|__________|_________________________|
    | ATM Package           |   A      |   Mandatory             |
    | Generic Media Package |   G      |   Mandatory             |
    | DTMF Package          |   D      |   Optional (e.g. in     |
    |                       |          |   IVR units)            |
    | Announcement          |   A      |   Optional (when gateway|
    | Server Package        |          |   can play announcement |
    |                       |          |   on ATM)               |
    | Script Package        |   Script |   Optional              |
    |_______________________|__________|_________________________|


7.2.5.  Network access service Termination

     (Editor's note: this Package definition is really a place holder.
     It will most probably have to be extensively reworked by the WG.)

A network access service (NAS) Termination describes the attachment of
the Context to a network access service such as a generic Internet
access or a tunnel to a private network server.

The NAS Termination is described by a single LocalTerminationDescriptor
parameter.  The RemoteTerminationDescriptor parameter is not used.  The
LocalTerminationDescriptor is described using SDP with the following
conventions:

*    Media description field (m) specifying the network access media,
     identified by the code "m=nas/xxxx", where "xxxx" describes the
     access control method that should be used for parameterizing the
     network access, as specified below. The field may also specify the
     port that should be used for contacting the server, as specified in
     the SDP syntax.

*    Connection address property (c=) specifying the address, or the
     domain name, of the server that implement the access control
     method. This property may also be specified at the session level.

*    Optionally, a bearer type attribute (a=bearer:) describing the type
     of data connection to be used, including the modem type.

*    Optionally, a framing type attribute (a=framing:) describing the
     type of framing that will be used on the channel.




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*    Optionally, attributes describing the called number (a=dialed:),
     the number to which the call was delivered (a=called:) and the cal-
     ling number (a=dialing:).

*    Optionally, attributes describing the range of addresses that could
     be used by the dialup client on its LAN (a=subnet:).

*    Optionally, an encryption key, encoded as specified in the SDP
     protocol(k=).

The connection address shall be encoded as specified in the SDP stan-
dard. It must be used in conjunction with the port specified in the
media line to access a server, whose type must be one of:

       __________________________________________________________
      | Method name|  Method description                        |
      |____________|____________________________________________|
      | radius     |  Authentication according                  |
      |            |  to the Radius protocol.                   |
      | tacacs     |  Authentication according                  |
      |            |  to the TACACS+ protocol.                  |
      | diameter   |  Authentication according                  |
      |            |  to the Diameter protocol.                 |
      | l2tp       |  Level 2 tunneling protocol.               |
      |            |  The address and port are those of the LNS.|
      | login      |  Local login. (There is normally           |
      |            |  no server for that method.)               |
      | none       |  No authentication required.               |
      |            |  (The call was probably vetted             |
      |            |  by the Call Agent.)                       |
      |____________|____________________________________________|


If needed, the gateway may use the key specified in the announcement to
access the service. That key, in particular, may be used for the estab-
lishment of an L2TP tunnel.

The bearer attribute is composed of a bearer name and an optional exten-
sion.  The bearer type specifies the type of modulation (modem name) or,
in the case of digital connections, the type of ISDN service (8 bits, 7
bits).  When an extension is present, it is separated from the bearer
name by a single slash (/).  The valid values of the bearer attribute
are defined in the following table:








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  ____________________________________________________________________
 | Type of bearer description      |  Example of values              |
 |_________________________________|_________________________________|
 | ITU modem standard              |  V.32, V.34, V.90.              |
 | ITU modem standard qualified    |  v.90/3com,                     |
 | by a manufacturer name          |  v.90/rockwell,                 |
 |                                 |  v.90/xxx                       |
 | Well known modem types          |  X2, K56flex                    |
 | ISDN transparent access, 64 kbps|  ISDN64                         |
 | ISDN64 + V.110                  |  ISDN64/V.110                   |
 | ISDN64 + V.120                  |  ISDN64/V.120                   |
 | ISDN transparent access, 56 kbps|  ISDN56                         |
 | Informal identification         |  (Requires coordination between |
 |                                 |  the Call Agent and the gateway)|
 |_________________________________|_________________________________|


The valid values of the framing attribute are defined in the following
table:

           _________________________________________________
          | Type of framing description|  Example of values|
          |____________________________|___________________|
          | PPP, asynchronous framing  |  ppp-asynch       |
          | PPP, HDLC framing          |  ppp-hdlc         |
          | SLIP, asynchronous         |  slip             |
          | Asynchronous, no framing   |  asynch           |
          |____________________________|___________________|


The network access authentication property provides instructions on the
access control that should be exercized for the data call. This optional
attribute is encoded as:

        "a=subnet:" <network type> <address type>
           <connection address> "/" <prefix length>


Where the properties "network type", "address type", and "connection
address" are formatted as defined for the connection address property
(c=) in SDP, and where the "prefix length" is a decimal representation
of the number of bits in the prefix.

Examples of SDP announcement for the network access service could be:

        v=0
        m=nas/radius
        c=IN IP4 radius.example.net



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        a=bearer:v.34
        a=framing:ppp-asynch
        a=dialed:18001234567
        a=called:12345678901
        a=dialing:12340567890

        v=0
        m=nas/none
        c=IN IP4 128.96.41.1
        a=subnet:IN IP4 123.45.67.64/26
        a=bearer:isdn64
        a=framing:ppp-sync
        a=dialed:18001234567
        a=dialing:2345678901

        v=0
        c=IN IP4 access.example.net
        m=nas/l2tp
        k=clear:some-shared-secret
        a=bearer:v.32
        a=framing:ppp-asynch
        a=dialed:18001234567
        a=dialing:2345678901


There is no default value of the properties defined for this Termination
Class.(Editor's note: we may have to define more specific Classes, such
as "Internet Access", for which the defaults would apply.)

The following statistics can be collected on NAS Terminations:

     Number of packets sent:
     The total number of NAS packets transmitted since starting
     transmission on this connection.

Number of octets sent:
     The total number of octets transmitted in NAS packets.

Number of packets received:
     The total number of packets received since starting reception on
     this connection.

Number of octets received:
     The total number of octets received in NAS packets.

Terminations of the NAS Class are expected to provide the following sup-
port for Event Packages:




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             ______________________________________________
            | Package    |   name |   support in NAS Class|
            |____________|________|_______________________|
            | NAS Package|   N    |   Mandatory           |
            |____________|________|_______________________|


8.  Acknowledgements

The authors would like to thank the fine crews of the numerous airlines
that carried them around the world to a succession of interesting meet-
ings, their family members whom they left alone during said meetings,
their colleagues and their staff.

We would also like to extend special thanks to the members of the MEGACO
design team, Nancy-M Greene, Glen Freundlich, David Auerbach, Rex Col-
dren, Dave Oran, Flemming Andreassen, Hong Liu, Michael Ramalho, Gur
Kimchi, Graeme Gibbs, Brian Hill, Ike Elliott, Bob Bell, and Matt Hol-
dredge.

In fact, we would like to thank all the members of the MEGACO working
group, and its chair, Tom Taylor.

9.  References

*    Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A
     Transport Protocol for Real-Time Applications", RFC 1889, January
     1996.

*    Schulzrinne, H., "RTP Profile for Audio and Video Conferences with
     Minimal Control", RFC 1890, January 1996

*    Handley, M, Jacobson, V., "SDP: Session Description Protocol", RFC
     2327, April 1998.

*    Handley, M., Schulzrinne, H., Schooler, E., and  J. Rosenberg,
     "Session Initiation Protocol (SIP)", RFC 2543, March 1999.

*    Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming
     Protocol (RTSP)", RFC 2326, April 1998.

*    ITU-T, Recommendation Q.761, "FUNCTIONAL DESCRIPTION OF THE ISDN
     USER PART OF SIGNALLING SYSTEM No. 7", (Malaga-Torremolinos, 1984;
     modified at Helsinki, 1993)

*    ITU-T, Recommendation Q.762, "GENERAL FUNCTION OF MESSAGES AND SIG-
     NALS OF THE ISDN USER PART OF SIGNALLING SYSTEM No. 7", (Malaga-
     Torremolinos, 1984; modified at Helsinki, 1993)



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*    ITU-T, Recommendation H.323 (02/98), "PACKET-BASED MULTIMEDIA COM-
     MUNICATIONS SYSTEMS."

*    ITU-T, Recommendation H.225, "Call Signaling Protocols and Media
     Stream Packetization for Packet Based Multimedia Communications
     Systems."

*    ITU-T, Recommendation H.245 (02/98), "CONTROL PROTOCOL FOR MUL-
     TIMEDIA COMMUNICATION."

*    Atkinson, R., "Security Architecture for the Internet Protocol."
     RFC 2401, November 1998.

*    Atkinson, R., "IP Authentication Header." RFC 2402, December 1998.

*    Atkinson, R., "IP Encapsulating Security Payload (ESP)." RFC 2406,
     November 1998.

*    Crocker, D., P. Overell, "Augmented BNF for Syntax Specifications:
     ABNF", RFC 2234, November 1997.

10.  Authors' Addresses

        Fernando Cuervo,
        Nortel Networks
        Ottawa, ON, Canada
        EMail: cuervo@nortelnetworks.com

        Christian Huitema
        Telcordia Technologies
        445 South Street
        Morristown, NJ 07960
        EMail: huitema@research.telcordia.com

        Keith Kelly
        NetSpeak Corporation
        902 Clint Moore Road, Suite 104
        Boca Raton, FL  33487
        EMail: keith@netspeak.com

        Brian Rosen
        FORE Systems
        1000 FORE Drive
        Warrendale, PA 15086
        EMail: brosen@eng.fore.com

        Paul Sijben
        Lucent Technologies



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        PO box 18
        1270 AA Huizen
        the Netherlands
        Phone: +31 35 687 4774
        Email: sijben@lucent.com

        Eric Zimmerer
        Level3 Communications
        1450 Infinite Drive
        Louisville, CO 80027
        EMail: eric.zimmerer@level3.com








































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