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RFC2805 - Media Gateway Control Protocol Architecture and Requirements

王朝other·作者佚名  2008-05-31
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Network Working Group N. Greene

Request for Comments: 2805 Nortel Networks

Category: Informational M. Ramalho

Cisco Systems

B. Rosen

Marconi

April 2000

Media Gateway Control Protocol Architecture and Requirements

Status of this Memo

This memo provides information for the Internet community. It does

not specify an Internet standard of any kind. Distribution of this

memo is unlimited.

Copyright Notice

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

Abstract

This document describes protocol requirements for the Media Gateway

Control Protocol between a Media Gateway Controller and a Media

Gateway.

Table of Contents

1. IntrodUCtion .............................................. 3

2. Terminology ............................................... 3

3. Definitions ............................................... 3

4. Specific functions assumed within the MG .................. 5

5. Per-Call Requirements ..................................... 6

5.1. Resource Reservation ................................. 6

5.2. Connection Requirements .............................. 7

5.3. Media Transformations ................................ 8

5.4. Signal/Event Processing and Scripting ................ 9

5.5. QoS/CoS .............................................. 10

5.6. Test Support ......................................... 11

5.7. Accounting ........................................... 11

5.8. Signalling Control ................................... 11

6. Resource Control .......................................... 12

6.1. Resource Status Management ........................... 12

6.2. Resource Assignment .................................. 13

7. Operational/Management Requirements ....................... 13

7.1. Assurance of Control/Connectivity .................... 13

7.2. Error Control ........................................ 14

7.3. MIB Requirements ..................................... 15

8. General Protocol Requirements ............................. 15

8.1. MG-MGC Association Requirements ...................... 16

8.2. Performance Requirements ............................. 17

9. Transport ................................................. 17

9.1. Assumptions made for underlying network .............. 17

9.2. Transport Requirements ............................... 18

10. Security Requirements .................................... 18

11. Requirements specific to particular bearer types ......... 19

11.1. Media-specific Bearer types ......................... 20

11.1.1. Requirements for TDM PSTN (Circuit) ............ 20

11.1.2. Packet Bearer type ............................. 22

11.1.3. Bearer type requirements for ATM ............... 23

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 ......... 27

11.2.4. Trunking/Access Gateway with text telephone .... 28

11.2.5. Network Access Server .......................... 29

11.2.6. Restricted Capability Gateway .................. 30

11.2.7. Multimedia Gateway ............................. 31

11.2.8. Audio Resource Function ........................ 32

11.2.9. Multipoint Control Units ........................ 42

12. References ............................................... 43

13. Acknowledgements ......................................... 43

14. Authors' Addresses ....................................... 44

15. Full Copyright Statement ................................. 45

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 RFC2119 [1] and

indicate 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

associations of resources hosted by the MG. They typically involve

two terminations, but may involve more.

* Line or Loop

An analogue or digital access connection from a user terminal which

carries 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

transcoding 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

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

terminate SS7 signaling in an SS7-Internet Gateway. The SG function

may also be co-resident with the MG function to process SCN

signalling associated 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.).

Digital 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.

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

supported 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).

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

associations between a given number terminations.

c. The MG is not required (or allowed) by the protocol to maintain

a sense of future time: a reservation remains in effect until

explicitly released by the MGC.

5.2. Connection Requirements

The protocol must:

a. Support connections involving packet and circuit bearer

terminations in any combination, including "hairpin" connections

(connections between two circuit connections within the same

MG).

b. Support connections involving TDM, Analogue, ATM, IP or FR

transport 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 suBTract 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

individually 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 protocol 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

priority than other connections.

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

logical identifier,

with a one-to-one mapping between a logical identifier and a

physical port.

m. Allow the MG to report events such as resource reservation and

connection 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

cancellation.

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. 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

adaptation) 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

parameter, 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

protocol 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.

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

(announcements, 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:

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

connection.

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

transmitted, 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.

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

homologated together as a mandatory requirement of using the

protocol;

i.e. it must be possible to optionally conceal signaling type

variation 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

supporting bearer terminations, media resources, and facility-

associated signalling channels, due to failures, recovery, or

administrative action. It must be able to report whether a

termination is in service or out of service.

b. Support administrative blocking and release of TDM circuit

terminations.

Note: as the above point only relates to ISUP-controlled circuits, 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

available 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 discovery mechanism should provide the MGC

with a method to determine 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 context 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

provide 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

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

outside 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 provide 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

transport re-establishment are typical sources of potentially

detrimental 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

out-of-service.

f. Allow the MG to request the MGC to release a termination and

communicate a reason.

g. Allow the MGC to specify, as a result of such a request its

decision 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

information 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.

8. General Protocol Requirements

The protocol must:

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

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 processing 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

control: 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 mechanism 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

initial 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

command must be rejected).

8.1. MG-MGC Association Requirements

The Protocol must:

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

example, protocol PDU sizes vs. transport MTU sizes needs to be

considered 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:

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

messages 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

completed. For example, aborting a command that has been

overtaken by events.

b. Support priority messages: The protocol shall allow a command

precedence to allow priority messages to supercede non-priority

messages.

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

association

b. Allow for preservation of the of control messages once the

association 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

network operator's MGC.

f. 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.

g. 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 protocol. The protocol must support all types of bearer types

listed in Table 1.

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

(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

variable ASPects of the content encoding, particularly including

channel 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:

n. specification of sub-channel media streams,

o. 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 connection parameter.

i. invoking of encryption/decryption on media flows and

specification 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 termination 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 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

physical 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:

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

connection 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.

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].

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

underlying 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.

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

c. Provide subrate and multirate connections for further study.

d. Provide the capability to support Reporting/generation of

per-trunk CAS signalling (DP, DTMF, MF, R2, J2, and national

variants).

e. 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.

f. 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

reception.

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.

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

conversation.

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 control 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.

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. 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:

* 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 signaled 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

tunnel, 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

mechanism (RADIUS/DIAMETER/..), access type (PPP/SLIP/..) after

restart or upgrade.

11.2.6. 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.

11.2.7. 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

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

requirement is that the protocol not prevent such applications.

11.2.8. 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

communications 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

requirements 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.

11.2.8.1. 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:

- 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.

Nesting 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 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

specifying 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.

11.2.8.2. 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

terminated 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

pattern.

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

collection, voice recording (if supported), and/or speech

recognition analysis (if supported) provide the following types

of prompts:

- Initial Prompt

- 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

collection.

- 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.

- 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

segment of the announcement, previous segment of the

announcement, next segment of the announcement, or the current

announcement segment.

11.2.8.3. 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

collection (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

- 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

segment of the announcement, previous segment of the

announcement, next segment of the announcement, or the current

announcement segment.

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

identifier 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.

11.2.8.4. Speech Recognition Module

The speech recognition module can be used for a number of speech

recognition applications, such as:

- Limited Vocabulary Isolated Speech Recognition (e.g., "yes",

"no", the number "four"),

- Limited Vocabulary Continuous Speech Feature Recognition (e.g.,

the utterance "four hundred twenty-three dollars"),and/or

- Continuous Speech Recognition (e.g., unconstrained speech

recognition 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 complete.

- 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

collection (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

- 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

segment of the announcement, previous segment of the

announcement, next segment of the announcement, or the current

announcement segment.

11.2.8.5. 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 speakers (identification task).

The Speaker Verification/Identification Module must support all of

the requirements in the Play Module in addition to the following

requirements:

a. Be able to download parameters, such as speaker templates

(verification 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.

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

(identification 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

collection (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 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.

11.2.8.6. Auditory Feature Extraction/Recognition Module

The auditory feature extraction/recognition module is engineered to

continuously 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

following 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).

11.2.8.7. 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.

11.2.9. 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. References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement

Levels", BCP 14, RFC2119, March 1997.

[2] ITU-T Recommendation Q.2630.1, AAL type 2 Signalling Protocol

(Capability Set 1), December 1999.

[3] ITU-T Recommendation H.341, Line Transmission of Non-Telephone

Signals, May 1999.

[4] ATM Forum Technical Committee, af-vtoa-0083.001, Voice and

Telephony Over ATM to the Desktop Specification, March 1999.

[5] ITU-T Recommendation H.323v3, Packet-based Multimedia

Communications Systems (includes Annex C - H.323 on ATM),

September 1999.

[6] ATM Forum Technical Committee, af-saa-0124.000, Gateway for

H.323 Media Transport Over ATM, May 1999.

[7] ITU-T Recommendation T.140, Protocol for Multimedia Application

Text Conversation, February 1998.

[8] ITU-T Recommendation V.18, Operational and Interworking

Requirements for DCEs Operating in Text Telephone Mode, February

1998.

[9] ITU-T Recommendation Q.931, Digital Subscriber Signalling System

No. 1 (DSS 1) - ISDN User - Network Interface Layer 3

Specification for Basic Call Control, May 1998.

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 Multiservice Switching Forum.

15. Authors' Addresses

Nancy Greene

Nortel Networks

P.O. Box 3511 Stn C

Ottawa, ON, Canada K1Y 4H7

Phone: (514) 271-7221

EMail: ngreene@nortelnetworks.com

Michael A. Ramalho

Cisco Systems

1802 Rue de la Port

Wall Township, NJ

Phone: +1.732.449.5762

EMail: mramalho@cisco.com

Brian Rosen

Marconi

1000 FORE Drive, Warrendale, PA 15086

Phone: (724) 742-6826

EMail:

brosen@eng.fore.com

16. Full Copyright Statement

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

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, 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 Standards 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 FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFCEditor function is currently provided by the

Internet Society.

 
 
 
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