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Internet Engineering Task Force                             Nancy Greene
INTERNET DRAFT                                           Nortel Networks
<draft-ietf-megaco-reqs-09.txt>                       Michael A. Ramalho
Category: Informational                                    Cisco Systems
Expires: June 9, 2000                                        Brian Rosen
                                                            Fore Systems


      Media Gateway control protocol architecture and requirements
             Nancy Greene, Michael A. Ramalho, Brian Rosen




Status of this memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. Internet-Drafts are working docu-
ments of the Internet Engineering Task Force (IETF), its areas, and its
working groups. Note that other groups may also distribute working docu-
ments as Internet-Drafts.

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

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

To view the list Internet-Draft Shadow Directories, see
http://www.ietf.org/shadow.html.

This document is a product of the Media Gateway Control (MEGACO) Working
Group of the Internet Engineering Task Force (IETF).  Comments should be
submitted to the mailing list megaco@standards.nortelnetworks.com.



Abstract

This document describes protocol requirements for the Media Gateway con-
trol protocol between a Media Gateway Controller and a Media Gateway.


Table of Contents





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        1.  Introduction ..............................................  4
        2.  Terminology ...............................................  4
        3.  Definitions ...............................................  4
        4.  Specific functions assumed within the MG ..................  5
        5.  Per-Call Requirements .....................................  7
           5.1.  Resource Reservation .................................  7
           5.2.  Connection Requirements ..............................  8
           5.3.  Media Transformations ................................  9
           5.4.  Signal/Event Processing and Scripting ................ 10
           5.5.  QoS/CoS .............................................. 11
           5.6.  Test Support ......................................... 11
           5.7.  Accounting ........................................... 11
           5.8.  Signalling Control ................................... 12
        6.  Resource Control .......................................... 12
           6.1.  Resource Status Management ........................... 12
           6.2.  Resource Assignment .................................. 14
        7.  Operational/Management Requirements ....................... 14
           7.1.  Assurance of Control/Connectivity .................... 14
           7.2.  Error Control ........................................ 15
           7.3.  MIB Requirements ..................................... 15
        8.  General Protocol Requirements ............................. 16
           8.1.  MG-MGC Association Requirements ...................... 17
           8.2.  Performance Requirements ............................. 17
        9.  Transport ................................................. 18
           9.1.  Assumptions made for underlying network .............. 18
           9.2.  Transport Requirements ............................... 18
        10.  Security Requirements .................................... 19
        11.  Requirements specific to particular bearer types ......... 20
           11.1.  Media-specific Bearer types ......................... 20
              11.1.1.  Requirements for TDM PSTN (Circuit) ............ 21
              11.1.2.  Packet Bearer type ............................. 22
              11.1.3.  Bearer type requirements for ATM ............... 23
                 11.1.3.1.  Addressing ................................ 23
                 11.1.3.2.  Connection related requirements ........... 24
                 11.1.3.3.  Media adaptation .......................... 25
                 11.1.3.4.  Reporting requirements .................... 26
                 11.1.3.5.  Functional requirements ................... 26
           11.2.  Application-Specific Requirements ................... 26
              11.2.1.  Trunking Gateway ............................... 26
              11.2.2.  Access Gateway ................................. 27
              11.2.3.  Trunking/Access Gateway with fax ports ......... 28
              11.2.4.  Trunking/Access Gateway with text telephone .... 28
              11.2.5.  Trunking/Access Gateway with conference ports .. 29
              11.2.6.  Network Access Server .......................... 29
              11.2.7.  Restricted Capability Gateway .................. 31
              11.2.8.  Multimedia Gateway ............................. 31
              11.2.9.  ARF Unit ....................................... 33



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              11.2.10. Multipoint Control Units ....................... 43
        12.  Full Copyright Statement ................................. 43
        13.  References ............................................... 44
        14.  Acknowledgements ......................................... 45
        15.  Authors' addresses ....................................... 45














































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1.  Introduction

This document describes requirements to be placed on the Media Gateway
control protocol. When the word protocol is used on its own in this
document it implicitly means the Media Gateway control protocol.

2.  Terminology

In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" are to be interpreted as described in RFC 2119 [1] and indi-
cate requirement levels for the protocol.


3.  Definitions

*    Connection

Under the control of a Media Gateway Controller (MGC), the Media Gateway
(MG) realizes connections. In this document, connections are associa-
tions of resources hosted by the MG. They typically involve two termina-
tions, but may involve more.

*    Line or Loop

An analogue or digital access connection from a user terminal which car-
ries user media content and telephony access signalling (DP, DTMF, BRI,
proprietary business set).

*    Media Gateway (MG) function

A Media Gateway (MG) function provides the media mapping and/or tran-
scoding functions between potentially dissimilar networks, one of which
is presumed to be a packet, frame or cell network.  For example, an MG
might terminate switched circuit network (SCN) facilities (trunks,
loops), packetize the media stream, if it is not already packetized, and
deliver packetized traffic to a packet network.  It would perform these
functions in the reverse order for media streams flowing from the packet
network to the SCN.

Media Gateways are not limited to SCN <-> packet/frame/cell functions: A
conference bridge with all packet interfaces could be an MG, as well as
an (IVR) interactive voice recognition unit, an audio resource function,
or a voice recognition system with a cell interface.

*    Media Gateway unit (MG-unit)

An MG-unit is a physical entity that contains an MG function and may



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also contain other functions, e.g. an SG function.

*    Media Gateway Controller (MGC) function

A Media Gateway Controller (MGC) function controls a MG.

*    Media Resource

Examples of media resources are codecs, announcements, tones, and
modems, interactive voice response (IVR) units, bridges, etc.

*    Signaling Gateway (SG) function

An SG function receives/sends SCN native signalling at the edge of a
data network. For example the SG function may relay, translate or ter-
minate SS7 signaling in an SS7-Internet Gateway. The SG function may
also be co-resident with the MG function to process SCN signalling asso-
ciated with line or trunk terminations controlled by the MG, such as the
"D" channel of an ISDN PRI trunk.

*    Termination

A termination is a point of entry and/or exit of media flows relative to
the MG. When an MG is asked to connect two or more terminations, it
understands how the flows entering and leaving each termination are
related to each other.

Terminations are, for instance, DS0's, ATM VCs and RTP ports. Another
word for this is bearer point.

*    Trunk

An analog or digital connection from a circuit switch which carries user
media content and may carry telephony signalling (MF, R2, etc.).  Digi-
tal trunks may be transported and may appear at the Media Gateway as
channels within a framed bit stream, or as an ATM cell stream. Trunks
are typically provisioned in groups, each member of which provides
equivalent routing and service.

*    Type of Bearer

A Type of Bearer definition provides the detailed requirements for its
particular application/bearer type. A particular class of Media Gateway,
for example, would support a particular set of Bearer types.







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4.  Specific functions assumed within the MG

This section provides an environment for the definition of the general
Media Gateway control protocol requirements.

MGs can be architected in many different ways depending where the media
conversions and transcoding (if required) are performed, the level of
programmability of resources, how conferences are supported, and how
associated signalling is treated. The functions assumed to be within the
MG must not be biased towards a particular architecture.

For instance, announcements in a MG could be provided by media resources
or by the bearer point resource or termination itself. Further, this
difference must not be visible to MGC: The MGC must be able to issue the
identical request to two different implementations and achieve the
identical functionality.

Depending on the application of the MG (e.g., trunking, residential),
some functions listed below will be more prominent than others, and in
some cases, functions may even disappear.

Although media adaptation is the essence of the MG, it is not necessary
for it to be involved every time. An MG may join two
terminations/resources of the same type (i.e., the MG behaves as a
switch). The required media conversion depends on the media type sup-
ported by the resources being joined together.

In addition to media adaptation function, resources have a number of
unique properties, for instance:

*    certain types of resources have associated signalling capabilities
     (e.g., PRI signalling, DTMF),

*    some resources perform maintenance functions (e.g., continuity
     tests),

*    the MGC needs to know the state changes of resources (e.g., a trunk
     group going out of service),

*    the MG retains some control over the allocation and control of some
     resources (e.g., resource name space: RTP port numbers).

Therefore, an MG realizes point-to-point connections and conferences,
and supports several resource functions. These functions include media
conversion, resource allocation and management, and event notifications.
Handling termination associated signalling is either done using event
notifications, or is handled by the signalling backhaul part of a MG-
unit (i.e. NOT directly handled by the MG).



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MGs must also support some level of system related functions, such as
establishing and maintaining some kind of MG-MGC association. This is
essential for MGC redundancy, fail-over and resource sharing.

Therefore, an MG is assumed to contain these functions:

*    Reservation and release, of resources

*    Ability to provide state of resources

*    Maintenance of resources - It must be possible to make maintenance
     operations independent of other termination functions, for
     instance, some maintenance states should not affect the resources
     associated with that resource . Examples of maintenance functions
     are loopbacks and continuity tests.

*    Connection management, including connection state.

*    Media processing, using media resources: these provide services
     such as transcoding, conferencing, interactive voice recognition
     units, audio resource function units. Media resources may or may
     not be directly part of other resources.

*    Incoming digit analysis for terminations, interpretation of scripts
     for terminations

*    Event detection and signal insertion for per-channel signalling

*    Ability to configure signalling backhauls (for example, a Sigtran
     backhaul)

*    Management of the association between the MGC and MG, or between
     the MGC and MG resources.


5.  Per-Call Requirements

5.1.  Resource Reservation

The protocol must:

a.   Support reservation of bearer terminations and media resources for
     use by a particular call and support their subsequent release
     (which may be implicit or explicit).

b.   Allow release in a single exchange of messages, of all resources
     associated with a particular set of connectivity and/or associa-
     tions between a given number terminations .



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c.   The MG is not required (or allowed) by the protocol to maintain a
     sense of future time: a reservation remains in effect until expli-
     citly released by the MGC.


5.2.  Connection Requirements

The protocol must:

a.   Support connections involving packet and circuit bearer termina-
     tions in any combination, including "hairpin" connections (connec-
     tions between two circuit connections within the same MG).

b.   Support connections involving TDM, Analogue, ATM, IP or FR tran-
     sport in any combination.

c.   Allow the specification of bearer plane (e.g. Frame Relay, IP,
     etc.) on a call by call basis.

d.   Support unidirectional, symmetric bi-directional, and asymmetric
     bi-directional flows of media.

e.   Support multiple media types (e.g. audio, text, video, T.120).

f.   Support point-to-point and point-to-multipoint connections.

g.   Support creation and modification of more complex flow topologies
     e.g. conference bridge capabilities.  Be able to add or delete
     media streams during a call or session, and be able to add or sub-
     tract participants to/from a call or session.

h.   Support inclusion of media resources into call or session as
     required.  Depending on the protocol and resource type, media
     resources may be implicitly included, class-assigned, or individu-
     ally assigned.

i.   Provide unambiguous specification of which media flows pass through
     a point and which are blocked at a given point in time, if the pro-
     tocol permits multiple flows to pass through the same point.

j.   Allow modifications of an existing termination, for example, use of
     higher compression to compensate for insufficient bandwidth or
     changing transport network connections.

k.   Allow the MGC to specify that a given connection has higher prior-
     ity than other connections.

l.   Allow a reference to a port/termination on the MG to be a logical



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     identifier,

     with a one-to-one mapping between a logical identifier and a physi-
     cal port.

m.   Allow the MG to report events such as resource reservation and con-
     nection completion.


5.3.  Media Transformations

The Protocol must:

a.   Support mediation/adaptation of flows between different types of
     transport

b.   Support invocation of additional processing such as echo cancella-
     tion.

c.   Support mediation of flows between different content encoding
     (codecs, encryption/decryption)

d.   Allow the MGC to specify whether text telephony/FAX/data modem
     traffic is to be terminated at the MG, modulated/demodulated, and
     converted to packets or forwarded by the MG in the media flow as
     voice band traffic.

e.   Allow the MGC to specify that Dual-Tone MultiFrequency (DTMF)
     digits or other line and trunk signals and general Multi-Frequency
     (MF) tones are to be processed in the MG and how these
     digits/signals/tones are to be handled. The MGC must be able to
     specify any of the following handling of such digits/signals/tones:


1.   The digits/signals/tones are to be encoded normally in the audio
     RTP stream (e.g., no analysis of the digits/signals/tones).

2.   Analyzed and sent to the MGC.

3.   Received from the MGC and inserted in the line-side audio stream.

4.   Analyzed and sent as part of a separate RTP stream (e.g., DTMF
     digits sent via a RTP payload separate from the audio RTP stream).

5.   Taken from a separate RTP stream and inserted in the line-side
     audio stream.

6.   Handled according to a script of instructions.



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     For all but the first case, an option to mute the
     digits/signals/tones with silence, comfort noise, or other means
     (e.g., notch filtering of some telephony tones) must be provided.
     As detection of these events may take up to tens of milliseconds,
     the first few milliseconds of such digit/signal/tone may be encoded
     and sent in the audio RTP stream before the digit/signal/tone can
     be verified. Therefore muting of such digits/signals/tones in the
     audio RTP stream with silence or comfort noise is understood to
     occur at the earliest opportunity after the digit/signal/tone is
     verified.



f.   Allow the MGC to specify signalled flow characteristics on circuit
     as well as on packet bearer connections, e.g. u-law/a-law.

g.   Allow for packet/cell transport adaptation only (no media adapta-
     tion) e.g. mid-stream (packet-to-packet)
     transpacketization/transcoding, or ATM AAL5 to and from ATM AAL2
     adaptation.

h.   Allow the transport of audio normalization levels as a setup param-
     eter, e.g., for conference bridging.

i.   Allow conversion to take place between media types e.g., text to
     speech and speech to text.


5.4.  Signal/Event Processing and Scripting

The Protocol must:

a.   Allow the MGC to enable/disable monitoring for specific supervision
     events at specific circuit terminations

b.   Allow the MGC to enable/disable monitoring for specific events
     within specified media streams

c.   Allow reporting of detected events on the MG to the MGC. The proto-
     col should provide the means to minimize the messaging required to
     report commonly-occurring event sequences.

d.   Allow the MGC to specify other actions (besides reporting) that the
     MG should take upon detection of specified events.

e.   Allow the MGC to enable and/or mask events.

f.   Provide a way for MGC to positively acknowledge event notification.



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g.   Allow the MGC to specify signals (e.g., supervision, ringing) to be
     applied at circuit terminations.

h.   Allow the MGC to specify content of extended duration (announce-
     ments, continuous tones) to be inserted into specified media flows.

i.   Allow the MGC to specify alternative conditions (detection of
     specific events, timeouts) under which the insertion of extended-
     duration signals should cease.

j.   Allow the MGC to download, and specify a script to be invoked on
     the occurrence of an event.

k.   Specify common events and signals to maximize MG/MGC interworking.

l.   Provide an extension mechanism for implementation defined events
     and signals with, for example, IANA registration procedures. It may
     be useful to have an Organizational Identifier (i.e. ITU, ETSI,
     ANSI, ) as part of the registration mechanism.

m.   The protocol shall allow the MGC to request the arming of a mid-
     call trigger even after the call has been set up.



5.5.  QoS/CoS

The Protocol must:

a.   Support the establishment of a bearer channel with a specified
     QoS/CoS.

b.   Support the ability to specify QoS for the connection between MGs,
     and by direction.

c.   Support a means to change QoS during a connection, as a whole and
     by direction.

d.   Allow the MGC to set QOS thresholds and receive notification when
     such thresholds cannot be maintained.

e.   Allow the jitter buffer parameters on RTP channels to be specified
     at connection setup.


5.6.  Test Support

The protocol must:



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a.   Support of the different types of PSTN Continuity Testing (COT) for
     both the originating and terminating ends of the circuit connection
     (2-wire and 4- wire).

b.   Specifically support test line operation (e.g. 103, 105, 108).



5.7.  Accounting

The protocol must:

a.   Support a common identifier to mark resources related to one con-
     nection.

b.   Support collection of specified accounting information from MGs.

c.   Provide the mechanism for the MGC to specify that the MG report
     accounting information automatically at end of call, in mid-call
     upon request, at specific time intervals as specified by the MGC
     and at unit usage thresholds as specified by the MGC.

d.   Specifically support collection of:

*    start and stop time, by media flow,

*    volume of content carried (e.g. number of packets/cells transmit-
     ted, number received with and without error, inter-arrival jitter),
     by media flow,

*    QOS statistics, by media flow.

e.   Allow the MGC to have some control over which statistics are
     reported, to enable it to manage the amount of information
     transferred.


5.8.  Signalling Control

Establishment and provisioning of signalling backhaul channels (via
SIGTRAN for example) is out of scope.  However, the MG must be capable
of supporting detection of events, and application of signals associated
with basic analogue line, and CAS type signalling.  The protocol must:

a.   Support the signalling requirements of analogue lines and Channel
     Associated Signaling (CAS).

b.   Support national variations of such signalling.



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c.   Provide mechanisms to support signalling without requiring MG-MGC
     timing constraints beyond that specified in this document.

d.   Must not create a situation where the MGC and the MG must be homo-
     logated together as a mandatory requirement of using the protocol;
     i.e. it must be possible to optionally conceal signaling type vari-
     ation from the MGC.

6.  Resource Control

6.1.  Resource Status Management

The protocol must:

a.   Allow the MG to report changes in status of physical entities sup-
     porting bearer terminations, media resources, and facility-
     associated signalling channels, due to failures, recovery, or
     administrative action. It must be able to report whether a termina-
     tion is in service or out of service.

b.   Support administrative blocking and release of TDM circuit termina-
     tions.

[Editor's Note: as the above point only relates to ISUP-controlled cir-
cuits, it may be unnecessary to require this since the MGC controls
their use.  However, it may be meaningful for MF and R2-signalled
trunks, where supervisory states are set to make the trunks unavailable
at the far end.]

c.   Provide a method for the MGC to request that the MG release all
     resources under the control of a particular MGC currently in use,
     or reserved, for any or all connections.

d.   Provide an MG Resource Discovery mechanism which must allow an MGC
     to discover what resources the MG has. Expressing resources can be
     an arbitrarily difficult problem and the initial release of the
     protocol may have a simplistic view of resource discovery.

     At a minimum, resource discovery must enumerate the names of avail-
     able circuit terminations and the allowed values for parameters
     supported by terminations.

     The protocol should be defined so that simple gateways could
     respond with a relatively short, pre-stored response to the
     discovery request mechanism. In general, if the protocol defines a
     mechanism that allows the MGC to specify a setting or parameter for
     a resource or connection in the MG, and MGs are not required to
     support all possible values for that setting or parameter, then the



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     discovery mechanism should provide the MGC with a method to deter-
     mine what possible values such settings or parameters are supported
     in a particular MG.

e.   Provide a mechanism to discover the current available resources in
     the MG, where resources are dynamically consumed by connections and
     the MGC cannot reasonably or reliably track the consumption of such
     resources. It should also be possible to discover resources
     currently in use, in order to reconcile inconsistencies between the
     MGC and the MG.

f.   Not require an MGC to implement an SNMP manager function in order
     to discover capabilities of an MG that may be specified during con-
     text establishment.


6.2.  Resource Assignment

The protocol must:

a.   Provide a way for the MG to indicate that it was unable to perform
     a requested action because of resource exhaustion, or because of
     temporary resource unavailability.

b.   Provide an ability for the MGC to indicate to an MG the resource to
     use for a call (e.g. DS0) exactly, or indicate a set of resources
     (e.g. pick a DS0 on a T1 line or a list of codec types) via a "wild
     card" mechanism from which the MG can select a specific resource
     for a call (e.g. the 16th timeslot, or G.723).

c.   Allow the use of DNS names and IP addresses to identify MGs and
     MGCs. This shall not preclude using other identifiers for MGs or
     MGCs when other non IP transport technologies for the protocol are
     used.


7.  Operational/Management Requirements

7.1.  Assurance of Control/Connectivity

To provide assurance of control and connectivity, the protocol must pro-
vide the means to minimize duration of loss of control due to loss of
contact, or state mismatches.

The protocol must:

a.   Support detection and recovery from loss of contact due to
     failure/congestion of communication links or due to MG or MGC



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     failure.

     Note that failover arrangements are one of the mechanisms which
     could be used to meet this requirement.

b.   Support detection and recovery from loss of synchronized view of
     resource and connection states between MGCs and MGs. (e.g. through
     the use of audits).

c.   Provide a means for MGC and MG to provide each other with booting
     and reboot indications, and what the MG's configuration is.

d.   Permit more than one backup MGC and provide an orderly way for the
     MG to contact one of its backups.

e.   Provide for an orderly switchback to the primary MGC after it
     recovers. How MGCs coordinate resources between themselves is out-
     side the scope of the protocol.

f.   Provide a mechanism so that when an MGC fails, connections already
     established can be maintained. The protocol does not have to pro-
     vide a capability to maintain connections in the process of being
     connected, but not actually connected when the failure occurs.

g.   The Protocol must allow the recovery or redistribution of traffic
     without call loss.


7.2.  Error Control

The protocol must:

a.   Allow for the MG to report reasons for abnormal failure of lower
     layer connections e.g. TDM circuit failure, ATM VCC failure.

b.   Allow for the MG to report Usage Parameter Control (UPC) events.

c.   Provide means to ameliorate potential synchronization or focused
     overload of supervisory/signaling events that can be detrimental to
     either MG or MGC operation. Power restoration or signaling tran-
     sport re-establishment are typical sources of potentially detrimen-
     tal signaling showers from MG to MGC or vice- versa.

d.   Allow the MG to notify the MGC that a termination was terminated
     and communicate a reason when a terminations is taken out-of-
     service unilaterally by the MG due to abnormal events.

e.   Allow the MGC to acknowledge that a termination has been taken



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     out-of-service.

f.   Allow the MG to request the MGC to release a termination and com-
     municate a reason.

g.   Allow the MGC to specify, as a result of such a request its deci-
     sion to take termination down, leave it as is or modify it.


7.3.  MIB Requirements

The Protocol must define a common MG MIB, which must be extensible, but
must:

a.   Provide information on:

*    mapping between resources and supporting physical entities.

*    statistics on quality of service on the control and signalling
     backhaul interfaces.

*    statistics required for traffic engineering within the MG.

b.   The protocol must allow the MG to provide to the MGC all informa-
     tion the MGC needs to provide in its MIB.

c.   MG MIB must support implementation of H.341 by either the MG, MGC,
     or both acting together.

 [Editor's Note: Discussion: MIB requirements should focus solely on the
management of the operation of the protocol itself.  Other MIBs cover
the topics suggested here, except possibly for the traffic engineering
statistics.  The point was raised that the MGC should not have to imple-
ment a manager function, because of the complications this would pose
for security administration.  This raises a requirement for the MGC to
be able to discover the resources and other necessary information per-
taining to a given MG by means of the protocol.  A suggestion was also
made that the MG needs to discover certain information about the MGC.

The mailing list is invited to comment, both on the proper Media Control
MIB requirements and on the requirements for discovery.]


8.  General Protocol Requirements

The protocol must:

a.   Support multiple operations to be invoked in one message and



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     treated as a single transaction.

b.   Be both modular and extensible. Not all implementations may wish to
     support all of the possible extensions for the protocol. This will
     permit lightweight implementations for specialized tasks where pro-
     cessing resources are constrained. This could be accomplished by
     defining particular profiles for particular uses of the protocol.


c.   Be flexible in allocation of intelligence between MG and MGC. For
     example, an MGC may want to allow the MG to assign particular MG
     resources in some implementations, while in others, the MGC may
     want to be the one to assign MG resources for use.

d.   Support scalability from very small to very large MGs: The protocol
     must support MGs with capacities ranging from one to millions of
     terminations.

e.   Support scalability from very small to very large MGC span of con-
     trol: The protocol should support MGCs that control from one MG to
     a few tens of thousands of MGs.

f.   Support the needs of a residential gateway that supports one to a
     few lines, and the needs of a large PSTN gateway supporting tens of
     thousands of lines. Protocol mechanisms favoring one extreme or the
     other should be minimized in favor of more general purpose mechan-
     ism applicable to a wide range of MGs. Where special purpose
     mechanisms are proposed to optimize a subset of implementations,
     such mechanisms should be defined as optional, and should have
     minimal impact on the rest of the protocol.

g.   Facilitate MG and MGC version upgrades independently of one
     another. The protocol must include a version identifier in the ini-
     tial message exchange.

h.   Facilitate the discovery of the protocol capabilities of the one
     entity to the other.

i.   Specify commands as optional (they can be ignored) or mandatory
     (the command must be rejected), and within a command, to specify
     parameters as optional (they can be ignored) or mandatory (the com-
     mand must be rejected).


8.1.  MG-MGC Association Requirements

The Protocol must:




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a.   Support the establishment of a control relationship between an MGC
     and an MG.

b.   Allow multiple MGCs to send control messages to an MG. Thus, the
     protocol must allow control messages from multiple signalling
     addresses to a single MG.

c.   Provide a method for the MG to tell an MGC that the MG received a
     command for a resource that is under the control of a different
     MGC.

d.   Support a method for the MG to control the rate of requests it
     receives from the MGC (e.g. windowing techniques, exponential back-
     off).

e.   Support a method for the MG to tell an MGC that it cannot handle
     any more requests.


8.2.  Performance Requirements

The protocol must:

a.   Minimize message exchanges between MG and MGC, for example during
     boot/reboot, and during continuity tests.

b.   Support Continuity test constraints which are a maximum of 200ms
     cross-MGC IAM (IAM is the name given to an SS7 connection setup
     msg) propagation delay, and a maximum of 200ms from end of dialing
     to IAM emission).

c.   Make efficient use of the underlying transport mechanism. For exam-
     ple, protocol PDU sizes vs. transport MTU sizes needs to be con-
     sidered in designing the protocol.

d.   Not contain inherent architectural or signaling constraints that
     would prohibit peak calling rates on the order of 140 calls/second
     on a moderately loaded network.

e.   Allow for default/provisioned settings so that commands need only
     contain non-default parameters.


9.  Transport

9.1.  Assumptions made for underlying network

The protocol must assume that the underlying network:



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a.   May be over large shared networks: proximity assumptions are not
     allowed.

b.   Does not assure reliable delivery of messages.

c.   Does not guarantee ordering of messages: Sequenced delivery of mes-
     sages associated with the same source of events is not assumed.

d.   Does not prevent duplicate transmissions.


9.2.  Transport Requirements

The protocol must:

a.   Provide the ability to abort delivery of obsolete messages at the
     sending end if their transmission has not been successfully com-
     pleted. For example, aborting a command that has been overtaken by
     events.

b.   Support priority messages: The protocol shall allow a command pre-
     cedence to allow priority messages to supercede non-priority mes-
     sages.

c.   Support of large fan-out at the MGC.

d.   Provide a way for one entity to correlate commands and responses
     with the other entity.

e.   Provide a reason for any command failure.

f.   Provide that loss of a packet not stall messages not related to the
     message(s) contained in the packet lost.

Note that there may be enough protocol reliability requirements here to
warrant a separate reliable transport layer be written apart from the
Media Gateway control protocol. Also need to compare Megaco reliable
transport requirements with similar Sigtran requirements.


10.  Security Requirements

Security mechanisms may be specified as provided in underlying transport
mechanisms, such as IPSEC.  The protocol, or such mechanisms, must:

a.   Allow for mutual authentication at the start of an MGC-MG associa-
     tion




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b.   Allow for preservation of the of control messages once the associa-
     tion has been established.

c.   Allow for optional confidentiality protection of control messages.
     The mechanism should allow a choice in the algorithm to be used.

d.   Operate across untrusted domains in a secure fashion.

e.   Support non-repudiation for a customer-located MG talking to a net-
     work operator's MGC.

g.   Define mechanisms to mitigate denial of service attacks

Note: the protocol document will need to include an extended discussion
of security requirements, offering more precision on each threat and
giving a complete picture of the defense including non-protocol measures
such as configuration.

h.   It would be desirable for the protocol to be able to pass through
     commonly-used firewalls.


11.  Requirements specific to particular bearer types

The bearer types listed in Table 1 can be packaged into different types
of MGs. Examples are listed in the following sections.  How they are
packaged is outside the scope of the general Media Gateway control pro-
tocol. The protocol must support all types of bearer types listed in
Table 1.






















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        Table 1: Bearer Types and Applications

        Bearer Type                   Applications       Transit Network
        ================================================================
        Trunk+ISUP                    trunking/access    IP, ATM, FR
                                      Voice,Fax,NAS,
                                      Multimedia

        Trunk+MF                      trunking/access    IP, ATM, FR
                                      Voice,Fax,NAS,
                                      Multimedia

        ISDN                          trunking/access    IP, ATM, FR
                                      Voice,Fax,NAS,
                                      Multimedia

        Analogue                      Voice,Fax,         IP, ATM, FR
                                      Text Telephony

        Termination in a Restricted   Voice,Fax,         IP, ATM, FR
        Capability Gateway            Text Telephony

        Application Termination       IVR,ARF, Announcement Server,
                                      Voice Recognition Server,...

        Multimedia H.323              H.323 Multimedia   IP, ATM, FR
                                      Gateway and MCU

        Multimedia H.320              H.323 GW and MCU   ISDN, IP, ATM, FR



11.1.  Media-specific Bearer Types

This section describes requirements for handling terminations attached
to specific types of networks.


11.1.1.  Requirements for TDM PSTN (Circuit)

This bearer type is applicable to a Trunking GW, Access GW, ...

The protocol must allow:

a.   the MGC to specify the encoding to use on the attached circuit.

b.   In general, if something is set by a global signalling protocol



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     (e.g. ISUP allows mu-Law or A-Law to be signaled using ISUP) then
     it must be settable by the protocol.

c.   TDM attributes:

*    Echo cancellation,

*    PCM encoding or other voice compression (e.g. mu-law or A-law),

*    encryption,

*    rate adaptation (e.g. V.110, or V.120).

d.   for incoming calls, identification of a specific TDM circuit
     (timeslot and facility).

e.   for calls outgoing to the circuit network, identification of a
     specific circuit or identification of a circuit group with the
     indication that the MG must select and return the identification of
     an available member of that group.

f.   specification of the default encoding of content passing to and
     from a given circuit, possibly on a logical or physical circuit
     group basis.

g.   specification at any point during the life of a connection of vari-
     able aspects of the content encoding, particularly including chan-
     nel information capacity.

h.   specification at any point during the life of a connection of loss
     padding to be applied to incoming and outgoing media streams at the
     circuit termination.

i.   specification at any point during the life of a connection of the
     applicability of echo cancellation to the outgoing media stream.

j.   Multi-rate calls to/from the SCN.

k.   H-channel (n x 64K) calls to/from the SCN.

l.   B channel aggregation protocols for creating high speed channels
     for multimedia over the SCN.

m.   Modem terminations and negotiations.


The protocol may also allow:




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l.   specification of sub-channel media streams,

m.   specification of multi-channel media streams.


11.1.2.  Packet Bearer Type

The protocol must be able to specify:

a.   ingress and egress coding (i.e. the way packets coming in and out
     are encoded) (including encryption).

b.   near and far-end ports and other session parameters for RTP and
     RTCP.

The protocol must support reporting of:

c.   re-negotiation of codec for cause - for further study

d.   on Trunking and Access Gateways, resources capable of more than one
     active connection at a time must also be capable of mixing and
     packet duplication.

The protocol must allow:

e.   specification of parameters for outgoing and incoming packet flows
     at separate points in the life of the connection (because far-end
     port addresses are typically obtained through a separate signalling
     exchange before or after the near-end port addresses are assigned).

f.   the possibility for each Media Gateway to allocate the ports on
     which it will receive packet flows (including RTCP as well as media
     streams) and report its allocations to the Media Gateway Controller
     for signalling to the far end.  Note that support of different IP
     backbone providers on a per call basis would require that the ports
     on which packets flow be selected by the MGC. (but only if the IP
     address of the MG is different for each backbone provider).

g.   the specification at any point during the life of a connection of
     RTP payload type and RTP session number for each RTP-encapsulated
     media flow.

h.   the ability to specify whether outgoing flows are to be uni-cast or
     multi-cast. Note that on an IP network this information is implicit
     in the destination address, but in other networks this is a connec-
     tion parameter.

i.   invoking of encryption/decryption on media flows and specification



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     of the associated algorithm and key.

The protocol should also allow:

j.   the MGC to configure non-RTP (proprietary or other) encapsulated
     packet flows.


11.1.3.  Bearer type requirements for ATM

This bearer type is applicable to Trunking GW, Access GW, ....


11.1.3.1.  Addressing

a.   The protocol must be able to specify the following termination
     attributes:

*    VC identifier,

*    VC identifier plus AAL2 slot, and variant of these allowing the
     gateway to choose (part of) the identifier,

*    remote termination network address, remote MG name.

b.   Allow specification of an ATM termination which is to be assigned
     to an MG connection as a VC identifier, a VC identifier plus AAL2
     slot, a wild-carded variant of either of these. A remote termina-
     tion network address, or a remote MG name could also be used when
     the MG can select the VC and change the VC during the life of the
     connection by using ATM signalling.

c.   Provide an indication by the MG of the VC identifier and possibly
     AAL2 slot of the termination actually assigned to a connection.

d.   Provide a means to refer subsequently to that termination.

e.   Refer to an existing VCC as the physical interface + Virtual Path
     Identifier (VPI) + Virtual Circuit Identifier (VCI).

f.   Where the VCC is locally established (SVCs signalled by the Gateway
     through UNI or PNNI signalling or similar), the VCC must be
     indirectly referred to in terms which are of significance to both
     ends of the VCC. For example, a global name or the ATM address of
     the ATM devices at each end of the VCC. However, it is possible/
     probable that there may be several VCCs between a given pair of ATM
     devices. Therefore the ATM address pair must be further resolved by
     a VCC identifier unambiguous within the context of the ATM address



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     pair.

g.   refer to a VCC as the Remote GW ATM End System Address + VCCI.

h.   allow the VCCI to be selected by the MG or imposed on the MG.

i.   support all ATM addressing variants (e.g. ATM End System Address
     (AESA) and E.164).


11.1.3.2.  Connection related requirements

The protocol must:

a.   Allow for the de-coupling of creation/deletion of the narrow-band
     connection from the creation/deletion of the underlying VCC.

b.   Allow for efficient disconnection of all connections associated
     with a physical port or VCC. As an example, this could aggregate
     disconnections across a broadband circuit which experienced a phy-
     sical error.

c.   Allow the connection established using this protocol to be carried
     over a VCC, which may be a:

*    PVC or SPVC,

*    an SVC established on demand, either by the MGC itself or by a
     broker acting on its behalf or,

*    an SVC originated as required by the local MG, or by the remote end
     to the local MG through UNI or PNNI signalling.

d.   Allow ATM transport parameters and QoS parameters to be passed to
     the MG.

e.   Allow blocking and unblocking of a physical interface, a VCC or an
     AAL1/AAL2 channel.

The protocol should:

f.   Where a VCC is required to be established on a per narrow-band call
     basis, allow all necessary information to be passed in one message.

11.1.3.3.  Media adaptation

The protocol must:




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a.   Allow AAL parameters to be passed to the MG.

b.   Allow AAL1/AAL2 multiple narrow-band calls to be mapped to a single
     VCC. For AAL2, these calls are differentiated within each VCC by a
     AAL2 channel identifier. An AAL2 connection may span more than 1
     VCC and transit AAL2 switching devices.  ITU Q.2630.1 [2] defines
     an end-to-end identifier called the Served User Generated Reference
     (SUGR). It carries information from the originating user of the
     AAL2 signalling protocol to the terminating user transparently and
     unmodified.


c.   Allow unambiguous binding of a narrow band call to an AAL2 connec-
     tion identifier, or AAL1 channel, within the specified VCC.

d.   Allow the AAL2 connection identifier, or AAL1 channel, to be
     selected by the MG or imposed on the MG.

e.   Allow the use of the AAL2 channel identifier (cid) instead of the
     AAL2 connection identifier.

f.   Allow the AAL2 voice profile to be imposed or negotiated before the
     start of the connection.  AAL2 allows for variable length packets
     and varying packet rates, with multiple codecs possible within a
     given profile. Thus a given call may upgrade or downgrade the codec
     within the lifetime of the call. Idle channels may generate zero
     bandwidth. Thus an AAL2 VCC may vary in bandwidth and possibly
     exceed its contract. Congestion controls within a gateway may react
     to congestion by modifying codec rates/types.

g.   Allow the MGC to instruct the MG on how individual narrow-band
     calls behave under congestion.

[Editor's Note: The ATM Forum is concerned that the above requirement
(g.) is not specific enough to handle all ATM traffic management capa-
bilities. They will provide a more specific requirement at a later
date.]

h.   Allow for the MGC to specify an AAL5 bearer, with the following
     choices:

*    Per ATM Forum standard AF-VTOA-0083 [4],

*    RTP with IP/UDP,

*    RTP without IP/IDP per H.323v2 Annex C [5],

*    Compressed RTP per ATM Forum AF-SAA-0124.000 [6].



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i.   Allow unambiguous binding of a narrow band call to an AAL1 channel
     within the specified VCC. (In AAL1, multiple narrow-band calls may
     be mapped to a single VCC.)

11.1.3.4.  Reporting requirements

The protocol should:

a.   Allow any end-of-call statistics to show loss/restoration of under-
     lying VCC within the calls duration, together with duration of
     loss.

b.   Allow notification, as requested by MGC, of any congestion
     avoidance actions taken by the MG.

The protocol must:

c.   Allow for ATM VCCs or AAL2 channels to be audited by the MGC.

d.   Allow changes in status of ATM VCCs or AAL2 channels to be notified
     as requested by the MGC.

e.   Allow the MGC to query the resource and endpoint availability.
     Resources may include VCCs, and DSPs. VCCs may be up or down. End-
     points may be connection-free, connected or unavailable.

11.1.3.5.  Functional requirements

The protocol must:

a.   Allow an MGC to reserve a bearer, and specify a route for it
     through the network.


11.2.  Application-Specific Requirements


11.2.1.  Trunking Gateway

A Trunking Gateway is an interface between SCN networks and Voice over
IP or Voice over ATM networks.  Such gateways typically interface to SS7
or other NNI signalling on the SCN and manage a large number of digital
circuits.

The protocol must:

a.   Provide circuit and packet-side loopback.




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b.   Provide circuit-side n x 64kbs connections.

c.   Provide subrate and multirate connections -for further study.

d.   Provide lawful wiretap capability

e.   Provide the capability to support Reporting/generation of per-trunk
     CAS signalling (DP, DTMF, MF, R2, J2, and national variants).

f.   Provide the capability to support reporting of detected DTMF events
     either digit-by-digit, as a sequence of detected digits with a
     flexible mechanism For the MG to determine the likely end of dial
     string, or in a separate RTP stream.

g.   Provide the capability to support ANI and DNIS generation and
     reception.

11.2.2.  Access Gateway

An Access Gateway connects UNI interfaces like ISDN (PRI and BRI) or
traditional analog voice terminal interfaces, to a Voice over IP or
Voice over ATM network, or Voice over Frame Relay network.

The Protocol must:

a.   Support detection and generation of analog line signaling (hook-
     state, ring generation).

b.   Provide the capability to support reporting of detected DTMF events
     either digit-by-digit, as a sequence of detected digits with a
     flexible mechanism For the MG to determine the likely end of dial
     string, or in a separate RTP stream.

c.   Not require scripting mechanisms, event buffering, digit map
     storage when implementing restricted function (1-2 line) gateways
     with very limited capabilities.

d.   Provide the capability to support CallerID generation and recep-
     tion.

Proxying of the protocol is for further study.


11.2.3.  Trunking/Access Gateway with fax ports


a.   the protocol must be able to indicate detection of fax media.




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b.   the protocol must be able to specify T.38 for the transport of the
     fax.

c    the protocol must be able to specify G.711 encoding for transport
     of fax tones across a packet network.


11.2.4.  Trunking/Access Gateway with text telephone access ports

An access gateway with ports capable of text telephone communication,
must provide communication between text telephones in the SCN and text
conversation channels in the packet network.

Text telephone capability of ports is assumed to be possible to combine
with other options for calls as described in section 11.2.6 (e.) on
"Adaptable NASes".

The port is assumed to adjust for the differences in the supported text
telephone protocols, so that the text media stream can be communicated
T.140 coded in the packet network without further transcoding [7].

The protocol must be capable of reporting the type of text telephone
that is connected to the SCN port. The foreseen types are the same as
the ones supported by ITU-T V.18:  DTMF, EDT, Baudot-45, Baudot-50,
Bell, V.21, Minitel and V.18. It should be possible to control which
protocols are supported. The SCN port is assumed to contain ITU-T V.18
functionality [8].

The protocol must be able to control the following functionality levels
of text telephone support:

a.   Simple text-only support: The call is set into text mode from the
     beginning of the call, in order to conduct a text-only conversa-
     tion.

b.   Alternating text-voice support: The call may begin in voice mode or
     text mode and, at any moment during the call, change mode on
     request by the SCN user. On the packet side, the two media streams
     for voice and text must be opened, and it must be possible to con-
     trol the feeding of each stream by the protocol.

c.   Simultaneous text and voice support: The call is performed in a
     mode when simultaneous text and voice streams are supported. The
     call may start in voice mode and during the call change state to a
     text-and-voice call.

A port may implement only level a, or any level combination of a, b and
c, always including level a.



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The protocol must support:

d.   A text based alternative to the interactive voice response, or
     audio resource functionality of the gateway when the port is used
     in text telephone mode.

e.   Selection of what national translation table to be used between the
     Unicode based T.140 and the 5-7 bit based text telephone protocols.

f.   Control of the V.18 probe message to be used on incoming calls.

11.2.5.  Trunking/Access Gateway with conference ports (Multipoint Pro-
cessing Unit)


11.2.6.  Network Access Server

A NAS is an access gateway, or Media Gateway (MG), which terminates
modem signals or synchronous HDLC connections from a network (e.g. SCN
or xDSL network) and provides data access to the packet network.  Only
those requirements specific to a NAS are described here.

Figure 1 provides a reference architecture for a Network Access Server
(NAS). Signaling comes into the MGC and the MGC controls the NAS.


                      +-------+        +-------+
           Signaling  |       |        |       |
           -----------+  MGC  +        |  AAA  |
                      |       |        |       |
                      +---+---+        +--+----+
                          |               |
                    Megaco|_______________|
                                          |
                                          |
                      +---+---+         ~~|~~~
            Bearer    |       |        (      )
           -----------+  NAS  +-------(   IP   )
                      |       |        (      )
                      +-------+         ~~~~~~

                  Figure 1: NAS reference architecture


The Protocol must support:

a.   Callback capabilities:




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*    Callback

b.   Modem calls.  The protocol must be able to specify the modem
     type(s) to be used for the call.

c.   Carriage of bearer information.  The protocol must be able to
     specify the data rate of the TDM connection (e.g., 64 kbit/s, 56
     kbit/s, 384 kbit/s), if this is available from the SCN.

d.   Rate Adaptation: The protocol must be able to specify the type of
     rate adaptation to be used for the call including indicating the
     subrate, if this is available from the SCN (e.g. 56K, or V.110 sig-
     naled in Bearer capabilities with subrate connection of 19.2kbit/s.

e.   Adaptable NASes: The protocol must be able to support multiple
     options for an incoming call to allow the NAS to dynamically select
     the proper type of call.  For example, an incoming ISDN call coded
     for "Speech" Bearer Capability could actually be a voice, modem,
     fax, text telephone, or 56 kbit/s synchronous call.  The protocol
     should allow the NAS to report back to the MGC the actual type of
     call once it is detected.

The 4 basic types of bearer for a NAS are:

1.   Circuit Mode, 64-kbps, 8-khz structured, Speech

2.   Circuit Mode, 64-kbps, 8-khz structured, 3.1-khz, Audio

3.   Circuit Mode, 64-kbps, 8-khz structured, Unrestricted Digital
     Transmission-Rate Adapted from 56-kbps

4.   Circuit Mode, 64-kbps, 8-khz structure, Unrestricted Digital
     Transmission

f.   Passage of Called and Calling Party Number information to the NAS
     from the MGC. Also, passage of Charge Number/Billing Number,
     Redirecting Number, and Original Call Number, if known, to the NAS
     from the MGC. If there are other Q.931 fields that need to be
     passed from the MGC to the MG, then it should be possible to pass
     them [9].

g.   Ability for the MGC to direct the NAS to connect to a specific tun-
     nel, for example to an LNS, or to an AAA server.

h.   When asked by the MGC, be able to report capability information,
     for example, connection types (V.34/V90/Synch ISDN..), AAA mechan-
     ism (RADIUS/DIAMETER/..), access type (PPP/SLIP/..) after restart
     or upgrade.



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11.2.7.  Restricted Capability Gateway

The requirements here may also be applied to small analog gateways, and
to cable/xDSL modems. See also the section on access gateways.

The Protocol must support:

a.   The ability to provide a scaled down version of the protocol. When
     features of the protocol are not supported, an appropriate error
     message must be sent. Appropriate default action must be defined.
     Where this is defined may be outside the scope of the protocol.

b.   The ability to provide device capability information to the MGC
     with respect to the use of the protocol.

11.2.8.  Multimedia Gateway

The protocol must have sufficient capability to support a multimedia
gateway. H.320 and H.324 are characterized by a single data stream with
multiple media streams multiplexed on it.

If the mapping is from H.320 or H.324 on the circuit side, and H.323 on
the packet side, it is assumed that the MG knows how to map respective
subchannels from H.320/H.324 side to streams on packet side. If extra
information is required when connecting two terminations, then it must
be supplied so that the connections are not ambiguous.

The Multimedia Gateway:

1)   should support Bonding Bearer channel aggregation,

2)   must support 2xB (and possibly higher rates) aggregation via H.221,

3)   must be able to dynamically change the size of audio, video and
     data channels within the h.320 multiplex,

4)   must react to changes in the H.320 multiplex on 20 msec boundaries,

5)   must support TCS4/IIS BAS commands,

6)   must support detection and creation of DTMF tones,

7)   should support SNMP MIBS as specified in H.341 [3]

a.   If some of the above cannot be handled by the MGC to MG protocol
     due to timing constraints, then it is likely that the H.245 to
     H.242 processing must take place in the MG. Otherwise, support for
     this functionality in the multimedia gateway are protocol



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     requirements.

b.   It must be possible on a call by call basis for the protocol to
     specify different applications. Thus, one call might be PSTN to
     PSTN under SS7 control, while the next might be ISDN/H.320 under
     SS7 control to H.323.  This is only one example; the key require-
     ment is that the protocol not prevent such applications.


11.2.9.  Audio Resource Function

An Audio Resource Function (ARF) consists of one or more functional
modules which can be deployed on an stand alone media gateway server
IVR, Intelligent Peripheral, speech/speaker recognition unit, etc. or a
traditional media gateway.  Such a media gateway is known as an Audio
Enabled Gateway (AEG) if it performs tasks defined in one or more of the
following ARF functional modules:

                   Play Audio,
                   DTMF Collect,
                   Record Audio,
                   Speech Recognition,
                   Speaker Verification/Identification,
                   Auditory Feature Extraction/Recognition, or
                   Audio Conferencing.


Additional ARF function modules that support human to machine communica-
tions through the use of telephony tones (e.g., DTMF) or auditory means
(e.g.  speech) may be appended to the AEG definition in future versions
of these requirements.

Generic scripting packages for any module must support all the require-
ments for that module. Any package extension for a given module must
include, by inheritance or explicit reference, the requirements for that
given module.

The protocol requirements for each of the ARF modules are provided in
the following subsections.


11.2.9.1.  Play Audio Module

a.   Be able to provide the following basic operation:

-    request an ARF MG to play an announcement.

b.   Be able to specify these play characteristics:



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-    Play volume

-    Play speed

-    Play iterations

-    Interval between play iterations

-    Play duration

c.   Permit the specification of voice variables such as DN, number,
     date,   time, etc.  The protocol must allow specification of both
     the value  (eg 234-3456), and well as the type (Directory number).

d.   Using the terminology that a segment is a unit of playable speech,
     or is an abstraction that is resolvable to a unit of playable
     speech, permit  specification of the following segment types:

-    A provisioned recording.

-    A block of text to be converted to speech.

-    A block of text to be displayed on a device.

-    A length of silence qualified by duration.

-    An algorithmically generated tone.

-    A voice variable, specified by type and value.  Given a variable
     type and value, the IVR/ARF unit would dynamically assemble the
     phrases required for its playback.

-    An abstraction that represents a sequence of audio segments.  Nest-
     ing of these abstractions must also be permitted.

An example of this abstraction is a sequence of audio segments, the
first of which is a recording of the words "The number you have dialed,"
followed by a Directory Number variable, followed by a recording of the
words "is no longer in service."

-    An abstraction that represents a set of audio segments and which is
     resolved to a single segment by a qualifier.  Nesting of these
     abstractions must be permitted.

For example take a set of audio segments recorded in different languages
all of which express the semantic concept "The number you have dialed is
no longer in service."  The set is resolved by a language qualifier. If
the qualifier is "French," the set resolves to the French version of



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this announcement.

In the case of a nested abstraction consisting of a set qualified by
language at one level and and a set qualified by gender at another
level,  it would be possible to specify that an announcement be played
in French  and spoken by a female voice.

e.   Provide two different methods of audio specification:

-    Direct specification of the audio components to be played by speci-
     fying the sequence of segments in the command itself.

-    Indirect specification of the audio components to be played by
     reference to a single identifier that resolves to a provisioned
     sequence of audio segments.


11.2.9.2.  DTMF Collect Module

The DTMF Collect Module must support all of the requirements in the Play
Module in addition to the following requirements:

a.   Be able to provide the following basic operation:

-    request an AEG to play an announcement, which may optionally ter-
     minated by DTMF, and then collect DTMF

b.   Be able to specify these event collection characteristics:

-    The number of attempts to give the user to enter a valid DTMF pat-
     tern.

c.   With respect to digit timers, allow the specification of:

-    Time allowed to enter the first digit.

-    Time allowed for user to enter each digit subsequent to the first
     digit.

-    Time allowed for user to enter a digit once the maximum expected
     number of digits has been entered.

d.   To be able to allow multiple prompt operations DTMF digit collec-
     tion, voice recording (if supported), and/or speech recognition
     analysis (if supported) provide the following types of prompts:

-    Initial Prompt




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-    Reprompt

-    Error prompt

-    Failure announcement

-    Success announcement.

e.   To allow digit pattern matching, allow the specification of:

-    maximum number of digits to collect.

-    minimum number of digits to collect.

-    a digit pattern using a regular expression.

f.   To allow digit buffer control, allow the specification of:

-    Ability to clear digit buffer prior to playing initial prompt
     (default is not to clear buffer).

-    Default clearing of buffer following playing of un-interruptible
     announcement segment.

-    Default clearing of buffer before playing a re-prompt in response
     to previous invalid input.

g.   Provide a method to specify DTMF interruptibility on a per audio
     segment basis.

h.   Allow the specification of definable key sequences for DTMF digit
     collection to:

-    Discard collected digits in progress, replay the prompt, and resume
     DTMF digit collection.

-    Discard collected digits in progress and resume DTMF digit collec-
     tion.

-    Terminate the current operation and return the terminating key
     sequence to the MGC.

i.   Provide a way to ask the ARF MG to support the following definable
     keys for digit collection and recording. These keys would then be
     able to be acted upon by the ARF MG:

-    A key to terminate playing of an announcement in progress.




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-    A set of one or more keys that can be accepted as the first digit
     to be collected.

-    A key that signals the end of user input.  The key may or may not
     be returned to the MGC along with the input already collected.

-    Keys to stop playing the current announcement and resume playing at
     the beginning of the first segment of the announcement, last seg-
     ment of the announcement, previous segment of the announcement,
     next segment of the announcement, or the current announcement seg-
     ment.


11.2.9.3.  Record Audio Module

The Record Module must support all of the requirements in the Play
Module as in addition to the following requirements:

a.   Be able to provide the following basic operation:

-    request an AEG to play an announcement and then record voice.

b.   Be able to specify these event collection characteristics:

-    The number of attempts to give the user to make a recording.

c.   With respect to recording timers, allow the specification of:

-    Time to wait for the user to initially speak.

-    The amount of silence necessary following the last speech segment
     for the recording to be considered complete.

-    The maximum allowable length of the recording  (not including pre-
     and post- speech silence).

d.   To be able to allow multiple prompt operations for DTMF digit col-
     lection (if supported), voice recording (if supported), speech
     recognition analysis (if supported) and/or speech
     verification/identification (if supported) and then to provide the
     following types of prompts:

-    Initial Prompt

-    Reprompt

-    Error prompt




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-    Failure announcement

-    Success announcement.

e.   Allow the specification of definable key sequences for digit
     recording or speech recognition analysis (if supported) to:

-    Discard recording in progress, replay the prompt, and resume
     recording.

-    Discard recording in progress and resume recording.

-    Terminate the current operation and return the terminating key
     sequence to the MGC.

f.   Provide a way to ask the ARF MG to support the following definable
     keys for recording. These keys would then be able to be acted upon
     by the ARF MG:

-    A key to terminate playing of an announcement in progress.

-    A key that signals the end of user input.  The key may or may not
     be returned to the MGC along with the input already collected.

-    Keys to stop playing the current announcement and resume playing at
     the beginning of the first segment of the announcement, last seg-
     ment of the announcement, previous segment of the announcement,
     next segment of the announcement, or the current announcement seg-
     ment.

g.   While audio prompts are usually provisioned in IVR/ARF MGs, support
     changing the provisioned prompts in a voice session rather than a
     data session.  In particular, with respect to audio management:

-    A method to replace provisioned audio with audio recorded during a
     call. The newly recorded audio must be accessible using the iden-
     tifier of the audio it replaces.

-    A method to revert from replaced audio to the original provisioned
     audio.

-    A method to take audio recorded during a call and store it such
     that it is accessible to the current call only through its own
     newly created unique identifier.

-    A method to take audio recorded during a call and store it such
     that it is accessible to any subsequent call through its own newly
     created identifier.



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11.2.9.4.  Speech Recognition Module

The speech recognition module can be used for a number of speech recog-
nition applications, such as:

-    Limited Vocabulary Isolated Speech Recognition (e.g., "yes", "no",
     the number "four"),

-    Limited Vocabulary Continuous Speech Feature Recognition (e.g., the
     utterace "four hundred twenty-three dollars"),and/or

-    Continuous Speech Recognition (e.g., unconstrained speech recogni-
     tion tasks).

The Speech Recognition Module must support all of the requirements in
the Play Module as in addition to the following requirements:

a.   Be able to provide the following basic operation: request an AEG to
     play an announcement and then perform speech recognition analysis.

b.   Be able to specify these event collection characteristics:

-    The number of attempts to give to perform speech recognition task.

c.   With respect to speech recognition analysis timers, allow the
     specification of:

-    Time to wait for the user to initially speak.

-    The amount of silence necessary following the last speech segment
     for the speech recognition analysis segment to be considered com-
     plete.

-    The maximum allowable length of the speech recognition analysis
     (not including pre- and post- speech silence).

d.   To be able to allow multiple prompt operations for DTMF digit col-
     lection  (if supported), voice recording (if supported), and/or
     speech recognition analysis and then to provide the following types
     of prompts:

-    Initial Prompt

-    Reprompt

-    Error prompt

-    Failure announcement



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-    Success announcement.

e.   Allow the specification of definable key sequences for digit
     recording (if supported) or speech recognition analysis to:

-    Discard  in process analysis, replay the prompt, and resume
     analysis.

-    Discard recording in progress and resume analysis.

-    Terminate the current operation and return the terminating key
     sequence to the MGC.

f.   Provide a way to ask the ARF MG to support the following definable
     keys for speech recognition analysis. These keys would then be able
     to be acted upon by the ARF MG:

-    A key to terminate playing of an announcement in progress.

-    A key that signals the end of user input.  The key may or may not
     be returned to the MGC along with the input already collected.

-    Keys to stop playing the current announcement and resume playing at
     the beginning of the first segment of the announcement, last seg-
     ment of the announcement, previous segment of the announcement,
     next segment of the announcement, or the current announcement seg-
     ment.


11.2.9.5.  Speaker Verification/Identification Module

The speech verification/identification module returns parameters that
indicate either the likelihood of the speaker to be the person that they
claim to be (verification task) or the likelihood of the speaker being
one of the persons contained in a set of previously characterized speak-
ers (identification task).

The Speaker Verification/Identification Module must support all of the
requirements in the Play Module in addition to the following require-
ments:

a.   Be able to download parameters, such as speaker templates (verifi-
     cation task) or sets of potential speaker templates (identification
     task), either prior to the session or in mid-session.

b.   Be able to download application specific software to the ARF either
     prior to the session or in mid-session.




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c.   Be able to return parameters indicating either the likelihood of
     the speaker to be the person that they claim to be (verification
     task) or the likelihood of the speaker being one of the persons
     contained in a set of previously characterized speakers (identifi-
     cation task).

d.   Be able to provide the following basic operation: request an AEG to
     play an announcement and then perform speech
     verification/identification analysis.

e.   Be able to specify these event collection characteristics: The
     number of attempts to give to perform speech
     verification/identification task.

f.   With respect to speech verification/identification analysis timers,
     allow the specification of:

-    Time to wait for the user to initially speak.

-    The amount of silence necessary following the last speech segment
     for the speech verification/identification analysis segment to be
     considered complete.

-    The maximum allowable length of the speech
     verification/identification analysis  (not including pre- and
     post-speech silence).

g.   To be able to allow multiple prompt operations for DTMF digit col-
     lection (if supported), voice recording, (if supported), speech
     recognition analysis (if supported) and/or speech
     verification/identification and provide the following types of
     prompts:

-    Initial Prompt

-    Reprompt

-    Error prompt

-    Failure announcement

-    Success announcement.

h.   Allow the specification of definable key sequences for digit
     recording (if supported) or speech recognition (if supported) in
     the speech verification/identification analysis to:

-    Discard speech verification/identification in analysis, replay the



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     prompt, and resume analysis.

-    Discard speech verification/identification analysis in progress and
     resume analysis.

-    Terminate the current operation and return the terminating key
     sequence to the MGC.

i.   Provide a way to ask the ARF MG to support the following definable
     keys for speech verification/identification analysis. These keys
     would then be able to be acted upon by the ARF MG:

-    A key to terminate playing of an announcement in progress.

-    A key that signals the end of user input.  The key may or may not
     be returned to the MGC along with the input already collected.

-    Keys to stop playing the current announcement and resume speech
     verification/identification at the beginning of the first segment
     of the announcement, last segment of the announcement, previous
     segment of the announcement, next segment of the announcement, or
     the current announcement segment.


11.2.9.6.  Auditory Feature Extraction/Recognition Module

The auditory feature extraction/recognition module is engineered to con-
tinuously monitor the auditory stream for the appearance of particular
auditory signals or speech utterances of interest and to report these
events (and optionally a signal feature representation of these events)
to network servers or MGCs.

The Auditory Feature Extraction/Recognition Module must support the fol-
lowing requirements:

a.   Be able to download application specific software to the ARF either
     prior to the session or in mid-session.

b.   Be able to download parameters, such as a representation of the
     auditory feature to extract/recognize, for prior to the session or
     in mid-session.

c.   Be able to return parameters indicating the auditory event found or
     a representation of the feature found (i.e., auditory feature).







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11.2.9.7.  Audio Conferencing Module

The protocol must support:

a.   a mechanism to create multi-point conferences of audio only and
     multimedia conferences in the MG.

b.   audio mixing; mixing multiple audio streams into a new composite
     audio stream

c.   audio switching; selection of incoming audio stream to be sent out
     to all conference participants.




11.2.10.  Multipoint Control Units

The protocol must support:

a.   a mechanism to create multi-point conferences of audio only and
     multimedia conferences in the MG.

b.   audio mixing; mixing multiple audio streams into a new composite
     audio stream

c.   audio switching; selection of incoming audio stream to be sent out
     to all conference participants.

d.   video switching; selection of video stream to be sent out to all
     conference participants

e.   lecture video mode; a video selection option where on video source
     is sent out to all conference users

f.   multi-point of T.120 data conferencing.

g.   The ability for the MG to function as an H.323 MP, and for the MGC
     to function as an H.323 MC, connected by this protocol
     (MEGACOP/H.248).  It should be possible for audio, data, and video
     MG/MPs to be physically separate while being under the control of a
     single MGC/H.323 MC.


12.  Full Copyright Statement

Copyright (C) The Internet Society (1999, 2000). All Rights Reserved.




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This document and translations of it may be copied and furnished to oth-
ers, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and dis-
tributed, in whole or in part, without restriction of any kind, provided
that the above copyright notice and this paragraph are included on all
such copies and derivative works. However, this document itself may not
be modified in any way, such as by removing the copyright notice or
references to the Internet Society or other Internet organizations,
except as needed for the purpose of developing Internet standards in
which case the procedures for copyrights defined in the Internet Stan-
dards process must be followed, or as required to translate it into
languages other than English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FIT-
NESS FOR A PARTICULAR PURPOSE."

13.  References


[1]  S. Bradner, "Key words for use in RFCs to Indicate Requirement Lev-
     els", RFC 2119, March 1997.

[2]  ITU-T Q.2630.1

[3]  ITU-T H.341

[4]  AF-VTOA-0083, ATM Forum document

[5]  ITU H.323v2 Annex C Recommendation

[6]  ATM Forum AF-SAA-0124.000

[7]  ITU-T T.140

[8]  ITU-T V.18

[9]  ITU-T Q.931







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14.  Acknowledgements

The authors would like to acknowledge the many contributors who debated
the media gateway control architecture and requirements on the IETF
Megaco and Sigtran mailing lists. Contributions to this document have
also been made through internet-drafts and discussion with members of
ETSI Tiphon, ITU-T SG16, TIA TR41.3.4, the ATM Forum, and the Multiser-
vice Switching Forum.

15.  Authors' addresses

        Nancy Greene
        Nortel Networks
        P.O. Box 3511 Stn C
        Ottawa, ON, Canada K1Y 4H7
        Tel: (514) 271-7221
        Email: ngreene@nortelnetworks.com

        Michael A. Ramalho
        Cisco Systems
        Wall Township, NJ
        Tel: +1.732.449.5762
        Email: mramalho@cisco.com

        Brian Rosen
        Fore Systems
        1000 FORE Drive, Warrendale, PA 15086
        Tel: (724) 742-6826
        Email: brosen@eng.fore.com





















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