As per Relevance of the word connection, we have this rfc below:
Network Working Group N.
Request for Comments: 2805 Nortel
Category: Informational M.
Cisco
B.
April 2000
Media Gateway Control Protocol Architecture and
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (2000). All Rights Reserved
This document describes protocol requirements for the Media
Control Protocol between a Media Gateway Controller and a
Gateway
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RFC 2805 MG Control Protocol Requirements April 2000
Table of
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
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RFC 2805 MG Control Protocol Requirements April 2000
1.
This document describes requirements to be placed on the
Gateway Control Protocol. When the word protocol is used on its
in this document it implicitly means the Media Gateway
Protocol
2.
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]
indicate requirement levels for the protocol
3.
*
Under the control of a Media Gateway Controller (MGC), the
Gateway (MG) realizes connections. In this document, connections
associations of resources hosted by the MG. They typically
two terminations, but may involve more
* Line or
An analogue or digital access connection from a user terminal
carries user media content and telephony access signalling (DP, DTMF
BRI, proprietary business set).
* Media Gateway (MG)
A Media Gateway (MG) function provides the media mapping and/
transcoding functions between potentially dissimilar networks, one
which is presumed to be a packet, frame or cell network.
example, an MG might terminate switched circuit network (SCN
facilities (trunks, loops), packetize the media stream, if it is
already packetized, and deliver packetized traffic to a
network. It would perform these functions in the reverse order
media streams flowing from the packet network to the SCN
Media Gateways are not limited to SCN <-> packet/frame/
functions: A conference bridge with all packet interfaces could be
MG, as well as an (IVR) interactive voice recognition unit, an
resource function, or a voice recognition system with a
interface
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* Media Gateway unit (MG-unit
An MG-unit is a physical entity that contains an MG function and
also contain other functions, e.g. an SG function
* Media Gateway Controller (MGC)
A Media Gateway Controller (MGC) function controls a MG
* Media
Examples of media resources are codecs, announcements, tones,
modems, interactive voice response (IVR) units, bridges, etc
* Signaling Gateway (SG)
An SG function receives/sends SCN native signalling at the edge of
data network. For example the SG function may relay, translate
terminate SS7 signaling in an SS7-Internet Gateway. The SG
may also be co-resident with the MG function to process
signalling associated with line or trunk terminations controlled
the MG, such as the "D" channel of an ISDN PRI trunk
*
A termination is a point of entry and/or exit of media flows
to the MG. When an MG is asked to connect two or more terminations
it understands how the flows entering and leaving each
are related to each other
Terminations are, for instance, DS0's, ATM VCs and RTP ports.
word for this is bearer point
*
An analog or digital connection from a circuit switch which
user media content and may carry telephony signalling (MF, R2, etc.).
Digital trunks may be transported and may appear at the Media
as channels within a framed bit stream, or as an ATM cell stream
Trunks are typically provisioned in groups, each member of
provides equivalent routing and service
* Type of
A Type of Bearer definition provides the detailed requirements
its particular application/bearer type. A particular class of
Gateway, for example, would support a particular set of Bearer types
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4. Specific functions assumed within the
This section provides an environment for the definition of
general Media Gateway Control Protocol requirements
MGs can be architected in many different ways depending where
media conversions and transcoding (if required) are performed,
level of programmability of resources, how conferences are supported
and how associated signalling is treated. The functions assumed to
within the MG must not be biased towards a particular architecture
For instance, announcements in a MG could be provided by
resources or by the bearer point resource or termination itself
Further, this difference must not be visible to MGC: The MGC must
able to issue the identical request to two different
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,
in some cases, functions may even disappear
Although media adaptation is the essence of the MG, it is
necessary for it to be involved every time. An MG may join
terminations/resources of the same type (i.e., the MG behaves as
switch). The required media conversion depends on the media
supported by the resources being joined together
In addition to media adaptation function, resources have a number
unique properties, for instance
* certain types of resources have associated
capabilities (e.g., PRI signalling, DTMF),
* some resources perform maintenance functions (e.g.,
tests),
* the MGC needs to know the state changes of resources (e.g.,
trunk group going out of service),
* the MG retains some control over the allocation and control
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
media conversion, resource allocation and management, and
notifications. Handling termination associated signalling is
done using event notifications, or is handled by the
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
establishing and maintaining some kind of MG-MGC association. This
essential for MGC redundancy, fail-over and resource sharing
Therefore, an MG is assumed to contain these functions
* Reservation and release, of
* Ability to provide state of
* Maintenance of resources - It must be possible to
maintenance operations independent of other
functions, for instance, some maintenance states should
affect the resources associated with that resource . Examples
maintenance functions are loopbacks and continuity tests
* Connection management, including connection state
* Media processing, using media resources: these provide
such as transcoding, conferencing, interactive voice
units, audio resource function units. Media resources may or
not be directly part of other resources
* Incoming digit analysis for terminations, interpretation
scripts for
* Event detection and signal insertion for per-channel
* Ability to configure signalling backhauls (for example,
Sigtran backhaul
* Management of the association between the MGC and MG, or
the MGC and MG resources
5. Per-Call
5.1. Resource
The protocol must
a. Support reservation of bearer terminations and media
for use by a particular call and support their
release (which may be implicit or explicit).
b. Allow release in a single exchange of messages, of all
associated with a particular set of connectivity and/
associations between a given number terminations
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c. The MG is not required (or allowed) by the protocol to
a sense of future time: a reservation remains in effect
explicitly released by the MGC
5.2. Connection
The protocol must
a. Support connections involving packet and circuit
terminations in any combination, including "hairpin"
(connections between two circuit connections within the
MG).
b. Support connections involving TDM, Analogue, ATM, IP or
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
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
topologies e.g. conference bridge capabilities. Be able to
or delete media streams during a call or session, and be able
add or subtract participants to/from a call or session
h. Support inclusion of media resources into call or session
required. Depending on the protocol and resource type,
resources may be implicitly included, class-assigned,
individually assigned
i. Provide unambiguous specification of which media flows
through a point and which are blocked at a given point in time
if the protocol permits multiple flows to pass through the
point
j. Allow modifications of an existing termination, for example,
of higher compression to compensate for insufficient
or changing transport network connections
k. Allow the MGC to specify that a given connection has
priority than other connections
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l. Allow a reference to a port/termination on the MG to be
logical identifier
with a one-to-one mapping between a logical identifier and
physical port
m. Allow the MG to report events such as resource reservation
connection completion
5.3. Media
The Protocol must
a. Support mediation/adaptation of flows between different types
b. Support invocation of additional processing such as
cancellation
c. Support mediation of flows between different content
(codecs, encryption/decryption
d. Allow the MGC to specify whether text telephony/FAX/data
traffic is to be terminated at the MG, modulated/demodulated
and converted to packets or forwarded by the MG in the
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
digits/signals/tones are to be handled. The MGC must be able
specify any of the following handling of
digits/signals/tones
1. The digits/signals/tones are to be encoded normally in the
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
stream
4. Analyzed and sent as part of a separate RTP stream (e.g.,
digits sent via a RTP payload separate from the audio
stream).
5. Taken from a separate RTP stream and inserted in the line-
audio stream
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6. Handled according to a script of instructions. For all but
first case, an option to mute the digits/signals/tones
silence, comfort noise, or other means (e.g., notch filtering
some telephony tones) must be provided. As detection of
events may take up to tens of milliseconds, the first
milliseconds of such digit/signal/tone may be encoded and
in the audio RTP stream before the digit/signal/tone can
verified. Therefore muting of such digits/signals/tones in
audio RTP stream with silence or comfort noise is understood
occur at the earliest opportunity after the digit/signal/tone
verified
f. Allow the MGC to specify signalled flow characteristics
circuit as well as on packet bearer connections, e.g. u-law/a
law
g. Allow for packet/cell transport adaptation only (no
adaptation) e.g. mid-stream (packet-to-packet
transpacketization/transcoding, or ATM AAL5 to and from ATM AAL
adaptation
h. Allow the transport of audio normalization levels as a
parameter, e.g., for conference bridging
i. Allow conversion to take place between media types e.g., text
speech and speech to text
5.4. Signal/Event Processing and
The Protocol must
a. Allow the MGC to enable/disable monitoring for
supervision events at specific circuit
b. Allow the MGC to enable/disable monitoring for specific
within specified media
c. Allow reporting of detected events on the MG to the MGC.
protocol should provide the means to minimize the
required to report commonly-occurring event sequences
d. Allow the MGC to specify other actions (besides reporting)
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
notification
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g. Allow the MGC to specify signals (e.g., supervision, ringing)
be applied at circuit terminations
h. Allow the MGC to specify content of extended
(announcements, continuous tones) to be inserted into
media flows
i. Allow the MGC to specify alternative conditions (detection
specific events, timeouts) under which the insertion
extended-duration signals should cease
j. Allow the MGC to download, and specify a script to be invoked
the occurrence of an event
k. Specify common events and signals to maximize MG/
interworking
l. Provide an extension mechanism for implementation defined
and signals with, for example, IANA registration procedures.
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
mid-call trigger even after the call has been set up
5.5. QoS/
The Protocol must
a. Support the establishment of a bearer channel with a
QoS/CoS
b. Support the ability to specify QoS for the connection
MGs, and by direction
c. Support a means to change QoS during a connection, as a
and by direction
d. Allow the MGC to set QOS thresholds and receive
when such thresholds cannot be maintained
e. Allow the jitter buffer parameters on RTP channels to
specified at connection setup
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5.6. Test
The protocol must
a. Support of the different types of PSTN Continuity Testing (COT
for both the originating and terminating ends of the
connection (2-wire and 4- wire).
b. Specifically support test line operation (e.g. 103, 105, 108).
5.7.
The protocol must
a. Support a common identifier to mark resources related to
connection
b. Support collection of specified accounting information from MGs
c. Provide the mechanism for the MGC to specify that the MG
accounting information automatically at end of call, in mid-
upon request, at specific time intervals as specified by the
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/
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
reported, to enable it to manage the amount of
transferred
5.8. Signalling
Establishment and provisioning of signalling backhaul channels (
SIGTRAN for example) is out of scope. However, the MG must
capable of supporting detection of events, and application of
associated with basic analogue line, and CAS type signalling.
protocol must
a. Support the signalling requirements of analogue lines
Channel Associated Signaling (CAS).
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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
homologated together as a mandatory requirement of using
protocol
i.e. it must be possible to optionally conceal signaling
variation from the MGC
6. Resource
6.1. Resource Status
The protocol must
a. Allow the MG to report changes in status of physical
supporting bearer terminations, media resources, and facility
associated signalling channels, due to failures, recovery,
administrative action. It must be able to report whether
termination is in service or out of service
b. Support administrative blocking and release of TDM
terminations
Note: as the above point only relates to ISUP-controlled circuits,
may be unnecessary to require this since the MGC controls their use
However, it may be meaningful for MF and R2-signalled trunks,
supervisory states are set to make the trunks unavailable at the
end
c. Provide a method for the MGC to request that the MG release
resources under the control of a particular MGC currently
use, or reserved, for any or all connections
d. Provide an MG Resource Discovery mechanism which must allow
MGC to discover what resources the MG has. Expressing
can be an arbitrarily difficult problem and the initial
of the protocol may have a simplistic view of
discovery
At a minimum, resource discovery must enumerate the names
available circuit terminations and the allowed values
parameters supported by terminations
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The protocol should be defined so that simple gateways
respond with a relatively short, pre-stored response to
discovery request mechanism. In general, if the protocol
a mechanism that allows the MGC to specify a setting
parameter for a resource or connection in the MG, and MGs
not required to support all possible values for that setting
parameter, then the discovery mechanism should provide the
with a method to determine what possible values such settings
parameters are supported in a particular MG
e. Provide a mechanism to discover the current available
in the MG, where resources are dynamically consumed
connections and the MGC cannot reasonably or reliably track
consumption of such resources. It should also be possible
discover resources currently in use, in order to
inconsistencies between the MGC and the MG
f. Not require an MGC to implement an SNMP manager function
order to discover capabilities of an MG that may be
during context establishment
6.2. Resource
The protocol must
a. Provide a way for the MG to indicate that it was unable
perform a requested action because of resource exhaustion,
because of temporary resource unavailability
b. Provide an ability for the MGC to indicate to an MG the
to use for a call (e.g. DS0) exactly, or indicate a set
resources (e.g. pick a DS0 on a T1 line or a list of
types) via a "wild card" mechanism from which the MG can
a specific resource for a call (e.g. the 16th timeslot,
G.723).
c. Allow the use of DNS names and IP addresses to identify MGs
MGCs. This shall not preclude using other identifiers for MGs
MGCs when other non IP transport technologies for the
are used
7. Operational/Management
7.1. Assurance of Control/
To provide assurance of control and connectivity, the protocol
provide the means to minimize duration of loss of control due to
of contact, or state mismatches
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The protocol must
a. Support detection and recovery from loss of contact due
failure/congestion of communication links or due to MG or
failure
Note that failover arrangements are one of the mechanisms
could be used to meet this requirement
b. Support detection and recovery from loss of synchronized view
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
booting and reboot indications, and what the MG's
is
d. Permit more than one backup MGC and provide an orderly way
the MG to contact one of its backups
e. Provide for an orderly switchback to the primary MGC after
recovers. How MGCs coordinate resources between themselves
outside the scope of the protocol
f. Provide a mechanism so that when an MGC fails,
already established can be maintained. The protocol does
have to provide a capability to maintain connections in
process of being connected, but not actually connected when
failure occurs
g. The Protocol must allow the recovery or redistribution
traffic without call loss
7.2. Error
The protocol must
a. Allow for the MG to report reasons for abnormal failure of
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
overload of supervisory/signaling events that can be
to either MG or MGC operation. Power restoration or
transport re-establishment are typical sources of
detrimental signaling showers from MG to MGC or vice-versa
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d. Allow the MG to notify the MGC that a termination was
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
out-of-service
f. Allow the MG to request the MGC to release a termination
communicate a reason
g. Allow the MGC to specify, as a result of such a request
decision to take termination down, leave it as is or modify it
7.3. MIB
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
backhaul interfaces
* statistics required for traffic engineering within the MG
b. The protocol must allow the MG to provide to the MGC
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
The protocol must
a. Support multiple operations to be invoked in one message
treated as a single transaction
b. Be both modular and extensible. Not all implementations may
to support all of the possible extensions for the protocol.
will permit lightweight implementations for specialized
where processing resources are constrained. This could
accomplished by defining particular profiles for particular
of the protocol
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c. Be flexible in allocation of intelligence between MG and MGC
For example, an MGC may want to allow the MG to
particular MG resources in some implementations, while
others, the MGC may want to be the one to assign MG
for use
d. Support scalability from very small to very large MGs:
protocol must support MGs with capacities ranging from one
millions of terminations
e. Support scalability from very small to very large MGC span
control: The protocol should support MGCs that control from
MG to a few tens of thousands of MGs
f. Support the needs of a residential gateway that supports one
a few lines, and the needs of a large PSTN gateway
tens of thousands of lines. Protocol mechanisms favoring
extreme or the other should be minimized in favor of
general purpose mechanism applicable to a wide range of MGs
Where special purpose mechanisms are proposed to optimize
subset of implementations, such mechanisms should be defined
optional, and should have minimal impact on the rest of
protocol
g. Facilitate MG and MGC version upgrades independently of
another. The protocol must include a version identifier in
initial message exchange
h. Facilitate the discovery of the protocol capabilities of the
entity to the other
i. Specify commands as optional (they can be ignored) or
(the command must be rejected), and within a command, to
parameters as optional (they can be ignored) or mandatory (
command must be rejected).
8.1. MG-MGC Association
The Protocol must
a. Support the establishment of a control relationship between
MGC and an MG
b. Allow multiple MGCs to send control messages to an MG. Thus,
protocol must allow control messages from multiple
addresses to a single MG
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c. Provide a method for the MG to tell an MGC that the MG
a command for a resource that is under the control of
different MGC
d. Support a method for the MG to control the rate of requests
receives from the MGC (e.g. windowing techniques,
back-off).
e. Support a method for the MG to tell an MGC that it cannot
any more requests
8.2. Performance
The protocol must
a. Minimize message exchanges between MG and MGC, for
during boot/reboot, and during continuity tests
b. Support Continuity test constraints which are a maximum of 200
cross-MGC IAM (IAM is the name given to an SS7 connection
msg) propagation delay, and a maximum of 200ms from end
dialing to IAM emission
c. Make efficient use of the underlying transport mechanism.
example, protocol PDU sizes vs. transport MTU sizes needs to
considered in designing the protocol
d. Not contain inherent architectural or signaling constraints
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
only contain non-default parameters
9.
9.1. Assumptions made for underlying
The protocol must assume that the underlying network
a. May be over large shared networks: proximity assumptions are
allowed
b. Does not assure reliable delivery of messages
c. Does not guarantee ordering of messages: Sequenced delivery
messages associated with the same source of events is
assumed
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d. Does not prevent duplicate transmissions
9.2. Transport
The protocol must
a. Provide the ability to abort delivery of obsolete messages
the sending end if their transmission has not been
completed. For example, aborting a command that has
overtaken by events
b. Support priority messages: The protocol shall allow a
precedence to allow priority messages to supercede non-
messages
c. Support of large fan-out at the MGC
d. Provide a way for one entity to correlate commands and
with the other entity
e. Provide a reason for any command failure
f. Provide that loss of a packet not stall messages not related
the message(s) contained in the packet lost
Note that there may be enough protocol reliability requirements
to warrant a separate reliable transport layer be written apart
the Media Gateway Control Protocol. Also need to compare
reliable transport requirements with similar Sigtran requirements
10. Security
Security mechanisms may be specified as provided in
transport mechanisms, such as IPSEC. The protocol, or
mechanisms, must
a. Allow for mutual authentication at the start of an MGC-
b. Allow for preservation of the of control messages once
association has been established
c. Allow for optional confidentiality protection of
messages. The mechanism should allow a choice in the
to be used
d. Operate across untrusted domains in a secure fashion
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e. Support non-repudiation for a customer-located MG talking to
network operator's MGC
f. Define mechanisms to mitigate denial of service
Note: the protocol document will need to include an
discussion of security requirements, offering more precision on
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
through commonly-used firewalls
11. Requirements specific to particular bearer
The bearer types listed in Table 1 can be packaged into
types of MGs. Examples are listed in the following sections.
they are packaged is outside the scope of the general Media
control protocol. The protocol must support all types of bearer
listed in Table 1.
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Table 1: Bearer Types and
Bearer Type Applications Transit
================================================================
Trunk+ISUP trunking/access IP, ATM,
Voice,Fax,NAS
Trunk+MF trunking/access IP, ATM,
Voice,Fax,NAS
ISDN trunking/access IP, ATM,
Voice,Fax,NAS
Analogue Voice,Fax, IP, ATM,
Text
Termination in a Restricted Voice,Fax, IP, ATM,
Capability Gateway Text
Application Termination IVR,ARF, Announcement Server
Voice Recognition Server,...
Multimedia H.323 H.323 Multimedia IP, ATM,
Gateway and
Multimedia H.320 H.323 GW and MCU ISDN, IP, ATM,
11.1. Media-specific Bearer
This section describes requirements for handling
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
(e.g. ISUP allows mu-Law or A-Law to be signaled using ISUP
then it must be settable by the protocol
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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
(timeslot and facility).
e. for calls outgoing to the circuit network, identification of
specific circuit or identification of a circuit group with
indication that the MG must select and return the
of an available member of that group
f. specification of the default encoding of content passing to
from a given circuit, possibly on a logical or physical
group basis
g. specification at any point during the life of a connection
variable aspects of the content encoding, particularly
channel information capacity
h. specification at any point during the life of a connection
loss padding to be applied to incoming and outgoing
streams at the circuit termination
i. specification at any point during the life of a connection
the applicability of echo cancellation to the outgoing
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
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
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11.1.2. Packet Bearer
The protocol must be able to specify
a. ingress and egress coding (i.e. the way packets coming in
out are encoded) (including encryption).
b. near and far-end ports and other session parameters for RTP
RTCP
The protocol must support reporting of
c. re-negotiation of codec for cause - for further
d. on Trunking and Access Gateways, resources capable of more
one active connection at a time must also be capable of
and packet duplication
The protocol must allow
e. specification of parameters for outgoing and incoming
flows at separate points in the life of the connection (
far-end port addresses are typically obtained through a
signalling exchange before or after the near-end port
are assigned).
f. the possibility for each Media Gateway to allocate the ports
which it will receive packet flows (including RTCP as well
media streams) and report its allocations to the Media
Controller for signalling to the far end. Note that support
different IP backbone providers on a per call basis
require that the ports on which packets flow be selected by
MGC. (but only if the IP address of the MG is different for
backbone provider).
g. the specification at any point during the life of a
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-
or multi-cast. Note that on an IP network this information
implicit in the destination address, but in other networks
is a connection parameter
i. invoking of encryption/decryption on media flows
specification of the associated algorithm and key
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The protocol should also allow
j. the MGC to configure non-RTP (proprietary or other)
packet flows
11.1.3. Bearer type requirements for
This bearer type is applicable to Trunking GW, Access GW, ....
11.1.3.1.
a. The protocol must be able to specify the following
attributes
* VC identifier
* VC identifier plus AAL2 slot, and variant of these allowing
gateway to choose (part of) the identifier
* remote termination network address, remote MG name
b. Allow specification of an ATM termination which is to
assigned to an MG connection as a VC identifier, a VC
plus AAL2 slot, a wild-carded variant of either of these.
remote termination network address, or a remote MG name
also be used when the MG can select the VC and change the
during the life of the connection by using ATM signalling
c. Provide an indication by the MG of the VC identifier
possibly AAL2 slot of the termination actually assigned to
connection
d. Provide a means to refer subsequently to that termination
e. Refer to an existing VCC as the physical interface +
Path Identifier (VPI) + Virtual Circuit Identifier (VCI).
f. Where the VCC is locally established (SVCs signalled by
Gateway through UNI or PNNI signalling or similar), the VCC
be indirectly referred to in terms which are of significance
both ends of the VCC. For example, a global name or the
address of the ATM devices at each end of the VCC. However,
is possible/probable that there may be several VCCs between
given pair of ATM devices. Therefore the ATM address pair
be further resolved by a VCC identifier unambiguous within
context of the ATM address pair
g. refer to a VCC as the Remote GW ATM End System Address + VCCI
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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
(AESA) and E.164).
11.1.3.2. Connection related
The protocol must
a. Allow for the de-coupling of creation/deletion of the narrow
band connection from the creation/deletion of the
VCC
b. Allow for efficient disconnection of all connections
with a physical port or VCC. As an example, this could
disconnections across a broadband circuit which experienced
physical error
c. Allow the connection established using this protocol to
carried over a VCC, which may be a
* PVC or SPVC
* an SVC established on demand, either by the MGC itself or by
broker acting on its behalf or
* an SVC originated as required by the local MG, or by the
end to the local MG through UNI or PNNI signalling
d. Allow ATM transport parameters and QoS parameters to be
to the MG
e. Allow blocking and unblocking of a physical interface, a VCC
an AAL1/AAL2 channel
The protocol should
f. Where a VCC is required to be established on a per narrow-
call basis, allow all necessary information to be passed in
message
11.1.3.3. Media
The protocol must
a. Allow AAL parameters to be passed to the MG
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b. Allow AAL1/AAL2 multiple narrow-band calls to be mapped to
single VCC. For AAL2, these calls are differentiated within
VCC by a AAL2 channel identifier. An AAL2 connection may
more than 1 VCC and transit AAL2 switching devices.
Q.2630.1 [2] defines an end-to-end identifier called the
User Generated Reference (SUGR). It carries information from
originating user of the AAL2 signalling protocol to
terminating user transparently and unmodified
c. Allow unambiguous binding of a narrow band call to an AAL
connection identifier, or AAL1 channel, within the
VCC
d. Allow the AAL2 connection identifier, or AAL1 channel, to
selected by the MG or imposed on the MG
e. Allow the use of the AAL2 channel identifier (cid) instead
the AAL2 connection identifier
f. Allow the AAL2 voice profile to be imposed or negotiated
the start of the connection. AAL2 allows for variable
packets and varying packet rates, with multiple codecs
within a given profile. Thus a given call may upgrade
downgrade the codec within the lifetime of the call.
channels may generate zero bandwidth. Thus an AAL2 VCC may
in bandwidth and possibly exceed its contract.
controls within a gateway may react to congestion by
codec rates/types
g. Allow the MGC to instruct the MG on how individual narrow-
calls behave under congestion
h. Allow for the MGC to specify an AAL5 bearer, with the
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 AAL
channel within the specified VCC. (In AAL1, multiple narrow-
calls may be mapped to a single VCC.)
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11.1.3.4. Reporting
The protocol should
a. Allow any end-of-call statistics to show loss/restoration
underlying VCC within the calls duration, together with
of loss
b. Allow notification, as requested by MGC, of any
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
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
The protocol must
a. Allow an MGC to reserve a bearer, and specify a route for
through the network
11.2. Application-Specific
11.2.1. Trunking
A Trunking Gateway is an interface between SCN networks and
over IP or Voice over ATM networks. Such gateways
interface to SS7 or other NNI signalling on the SCN and manage
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
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d. Provide the capability to support Reporting/generation
per-trunk CAS signalling (DP, DTMF, MF, R2, J2, and
variants).
e. Provide the capability to support reporting of detected
events either digit-by-digit, as a sequence of detected
with a flexible mechanism For the MG to determine the likely
of dial string, or in a separate RTP stream
f. Provide the capability to support ANI and DNIS generation
reception
11.2.2. Access
An Access Gateway connects UNI interfaces like ISDN (PRI and BRI)
traditional analog voice terminal interfaces, to a Voice over IP
Voice over ATM network, or Voice over Frame Relay network
The Protocol must
a. Support detection and generation of analog line
(hook-state, ring generation).
b. Provide the capability to support reporting of detected
events either digit-by-digit, as a sequence of detected
with a flexible mechanism For the MG to determine the likely
of dial string, or in a separate RTP stream
c. Not require scripting mechanisms, event buffering, digit
storage when implementing restricted function (1-2 line
gateways with very limited capabilities
d. Provide the capability to support CallerID generation
reception
Proxying of the protocol is for further study
11.2.3. Trunking/Access Gateway with fax
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
the fax
c. the protocol must be able to specify G.711 encoding
transport of fax tones across a packet network
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11.2.4. Trunking/Access Gateway with text telephone access
An access gateway with ports capable of text telephone communication
must provide communication between text telephones in the SCN
text conversation channels in the packet network
Text telephone capability of ports is assumed to be possible
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
text telephone protocols, so that the text media stream can
communicated T.140 coded in the packet network without
transcoding [7].
The protocol must be capable of reporting the type of text
that is connected to the SCN port. The foreseen types are the same
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
protocols are supported. The SCN port is assumed to contain ITU-
V.18 functionality [8].
The protocol must be able to control the following
levels of text telephone support
a. Simple text-only support: The call is set into text mode
the beginning of the call, in order to conduct a text-
conversation
b. Alternating text-voice support: The call may begin in voice
or text mode and, at any moment during the call, change mode
request by the SCN user. On the packet side, the two
streams for voice and text must be opened, and it must
possible to control the feeding of each stream by the protocol
c. Simultaneous text and voice support: The call is performed in
mode when simultaneous text and voice streams are supported.
call may start in voice mode and during the call change state
a text-and-voice call
A port may implement only level a, or any level combination of a,
and c, always including level a
The protocol must support
d. A text based alternative to the interactive voice response,
audio resource functionality of the gateway when the port
used in text telephone mode
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e. Selection of what national translation table to be used
the Unicode based T.140 and the 5-7 bit based text
protocols
f. Control of the V.18 probe message to be used on incoming calls
11.2.5. Network Access
A NAS is an access gateway, or Media Gateway (MG), which
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
Server (NAS). Signaling comes into the MGC and the MGC controls
NAS
+-------+ +-------+
Signaling | | | |
-----------+ MGC + | AAA |
| | | |
+---+---+ +--+----+
| |
Megaco|_______________|
|
|
+---+---+ ~~|~~~
Bearer | | ( )
-----------+ NAS +-------( IP )
| | ( )
+-------+ ~~~~~~
Figure 1: NAS reference
The Protocol must support
a. Callback capabilities
*
b. Modem calls. The protocol must be able to specify the
type(s) to be used for the call
c. Carriage of bearer information. The protocol must be able
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
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d. Rate Adaptation: The protocol must be able to specify the
of rate adaptation to be used for the call including
the subrate, if this is available from the SCN (e.g. 56K,
V.110 signaled in Bearer capabilities with subrate connection
19.2kbit/s).
e. Adaptable NASes: The protocol must be able to support
options for an incoming call to allow the NAS to
select the proper type of call. For example, an incoming
call coded for "Speech" Bearer Capability could actually be
voice, modem, fax, text telephone, or 56 kbit/s
call. The protocol should allow the NAS to report back to
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,
2. Circuit Mode, 64-kbps, 8-khz structured, 3.1-khz,
3. Circuit Mode, 64-kbps, 8-khz structured, Unrestricted
Transmission-Rate Adapted from 56-
4. Circuit Mode, 64-kbps, 8-khz structure, Unrestricted
f. Passage of Called and Calling Party Number information to
NAS from the MGC. Also, passage of Charge Number/Billing Number
Redirecting Number, and Original Call Number, if known, to
NAS from the MGC. If there are other Q.931 fields that need
be passed from the MGC to the MG, then it should be possible
pass them [9].
g. Ability for the MGC to direct the NAS to connect to a
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..),
mechanism (RADIUS/DIAMETER/..), access type (PPP/SLIP/..)
restart or upgrade
11.2.6. Restricted Capability
The requirements here may also be applied to small analog gateways
and to cable/xDSL modems. See also the section on access gateways
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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
error message must be sent. Appropriate default action must
defined. Where this is defined may be outside the scope of
protocol
b. The ability to provide device capability information to the
with respect to the use of the protocol
11.2.7. Multimedia
The protocol must have sufficient capability to support a
gateway. H.320 and H.324 are characterized by a single data
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
respective subchannels from H.320/H.324 side to streams on
side. If extra information is required when connecting
terminations, then it must be supplied so that the connections
not ambiguous
The Multimedia Gateway
1) should support Bonding Bearer channel aggregation
2) must support 2xB (and possibly higher rates) aggregation
H.221,
3) must be able to dynamically change the size of audio, video
data channels within the h.320 multiplex
4) must react to changes in the H.320 multiplex on 20
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
due to timing constraints, then it is likely that the H.245
H.242 processing must take place in the MG. Otherwise,
for this functionality in the multimedia gateway are
requirements
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b. It must be possible on a call by call basis for the protocol
specify different applications. Thus, one call might be PSTN
PSTN under SS7 control, while the next might be ISDN/H.320
SS7 control to H.323. This is only one example; the
requirement is that the protocol not prevent such applications
11.2.8. Audio Resource
An Audio Resource Function (ARF) consists of one or more
modules which can be deployed on an stand alone media gateway
IVR, Intelligent Peripheral, speech/speaker recognition unit, etc.
a traditional media gateway. Such a media gateway is known as
Audio Enabled Gateway (AEG) if it performs tasks defined in one
more of the following ARF functional modules
Play Audio
DTMF Collect
Record Audio
Speech Recognition
Speaker Verification/Identification
Auditory Feature Extraction/Recognition,
Audio Conferencing
Additional ARF function modules that support human to
communications through the use of telephony tones (e.g., DTMF)
auditory means (e.g. speech) may be appended to the AEG
in future versions of these requirements
Generic scripting packages for any module must support all
requirements for that module. Any package extension for a
module must include, by inheritance or explicit reference,
requirements for that given module
The protocol requirements for each of the ARF modules are provided
the following subsections
11.2.8.1. Play Audio
a. Be able to provide the following basic operation
