SIST ETS 300 675 E1:2003

• Abstract:

  To prepare a stage one description for an Audiographic conference teleservice in the ISDN.

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.080 - Integrated Services Digital Network (ISDN)
• ICS: 33.160.60 - Multimedia systems and teleconferencing equipment
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Ref Project: ETSI ETS 300 675 ed.1 (1996-11) - Integrated Services Digital Network (ISDN); Audiographic conference teleservice; Service description

Published by SIST, SIST ETS 300 675 E1:2003 is the Slovenian adoption of ETS 300 675 Edition 1 from ETSI. It specifies the stage one service description for the Integrated Services Digital Network (ISDN) audiographic conference teleservice. The document is for people who need the service model, interworking rules, and attribute view of a real-time conferencing service that carries speech, control signals, and data.

What does SIST ETS 300 675 E1:2003 specify?

SIST ETS 300 675 E1:2003 specifies the audiographic conference teleservice from the user’s point of view. It covers the basic service description, call behaviour, multipoint operation, interworking, and the static service attributes used to characterize the service in ISDN.

The document stays at stage one level, so it describes what the service is and how it behaves, not the detailed human interface or test methods. Charging principles are outside its scope, and general attribute values are left out.

It is organized into nine main clauses and three informative annexes.

Annex	What it covers
Annex A	Relation between standards and recommendations relevant to the audiographic conference service
Annex B	Applicability of supplementary services to the audiographic conference teleservice
Annex C	Bibliography

What are the key requirements of SIST ETS 300 675 E1:2003?

SIST ETS 300 675 E1:2003 defines a real-time service in which speech, conference control, and data are exchanged over one or more circuit-mode 64 kbit/s connections in ISDN. In practice, that means implementers have to support both a simple one-connection case and a multi-connection conference case.

Service model and facilities

Clause 5.1 splits the service into two cases:

• one circuit-mode 64 kbit/s connection
• two or more circuit-mode 64 kbit/s connections

That distinction matters because the first call carries the core speech and data path, while later calls extend the conference.

Clause 5.2.1 requires handsfree audio for two or more participants at each site, with simultaneous listening and speaking. The speech transmission bandwidth is nominally 7 kHz, which is important for natural conference audio and for deciding when bandwidth may be reduced in interworking.

Clause 5.2.2 requires a conference control facility for call establishment, call termination, mode control, and control signals such as floor requests and tokens. At minimum, this is based on ETS 300 144 and ETS 300 143; T.122 and T.124 can be used for improved performance.

Clause 5.2.3 requires a data transmission facility based on the data channels defined in ETS 300 144, with T.123 recommended for better performance. Clause 5.2.4 adds graphics transmission, and clause 5.3 allows optional still picture and file transfer applications using MCS.

Call handling and multipoint operation

Clause 6.1 allows the service to be provided by prior arrangement or as a generally available service. It also allows subscription options such as the maximum number of information channels and the maximum number of total calls on an interface. For a buyer or network planner, this is the part that drives provisioning limits.

Clause 6.2 requires Call 1 to be established before any subsequent calls. Call 1 sets up speech and data, while subsequent calls are used for data communication after end-to-end mode initialization. The document also requires network indications during setup, including acknowledgement to the calling user and arrival indication to the called user.

Clause 6.2.3 covers termination in point-to-point and multipoint conferences. In a multipoint conference, the MCU or a user with chair control can control the end of the whole conference. Clause 6.2.5 describes the MCU’s role: access, multiplexing and demultiplexing, audio mixing or switching, control-message analysis, routing, optional encryption, and terminal interconnection.

Clause 6.3 covers exceptional cases such as improper service requests, invalid ISDN numbers, busy users, non-responding terminals, congestion, and retention of call information. The retention timer is a network option and is greater than 15 seconds.

Interworking, fallback, and service attributes

Clause 7 requires intercommunication with 3,1 kHz and 7 kHz ISDN terminals and interworking with the Public Switched Telephone Network (PSTN). Fall-back to telephony 3,1 kHz or telephony 7 kHz is part of the service behaviour unless the calling user blocks fallback.

Clause 7.2 extends the same logic to private ISDNs, and clause 7.3 requires interoperability with restricted networks using the procedures in H.242 clause 13. For implementers, this is the part that determines whether the terminal can still complete a call when the far end or the network cannot support the full audiographic conference service.

Clause 8 links the service to supplementary services. If inband communication is interrupted, the network has to provide an appropriate signal in the B-channel, and inband communication has to return to mode 0 before services such as call hold are invoked.

Clause 9 gives the static attribute view. Tables 2 and 3 cover low-layer information transfer attributes for Call 1 and later calls, and tables 4 and 5 cover access attributes for the same cases. For systems engineering, this is the part that maps the service to ISDN attribute terminology.

What terms does SIST ETS 300 675 E1:2003 define?

SIST ETS 300 675 E1:2003 defines the service vocabulary used to describe the teleservice.

• Integrated Services Digital Network (ISDN) - a digital network that provides connections between user-network interfaces.
• teleservice - a telecommunication service that includes the terminal functions needed for communication between users.
• fall-back - the mechanism that turns an audiographic conference call into an accepted alternative teleservice, such as telephony 7 kHz or telephony 3,1 kHz.
• Multipoint Control Unit (MCU) - equipment in the network or terminal that connects several terminals and processes audiovisual signals for them.
• restricted network - a network with multiples of 64 kbit/s links where only multiples of 56 kbit/s are usable by terminals.
• retention timer - the network timer that keeps call information after busy or termination conditions.
• Multipoint Communication Service (MCS) - the multipoint service framework used for conferencing applications.
• Multi Layer Protocols (MLP) - the protocol family defined in the ITU-T T.120 series.

Who uses SIST ETS 300 675 E1:2003?

SIST ETS 300 675 E1:2003 is used by ISDN service providers, terminal manufacturers, MCU designers, and interoperability engineers. It is also relevant to network operators and procurement teams that need to define conferencing capabilities, subscription limits, fallback behaviour, and compatibility with PSTN and private ISDNs.

In practice, it helps with service planning, terminal implementation, conference bridge design, and checking how the service interacts with supplementary services.

What changed in SIST ETS 300 675 E1:2003 from the previous edition?

SIST ETS 300 675 E1:2003 is stated to be identical with ETS 300 675 Edition 1.

Which standards are used with SIST ETS 300 675 E1:2003?

SIST ETS 300 675 E1:2003 builds on a set of referenced ISDN and conferencing standards and recommendations.

Reference	What it contributes
CCITT Recommendation I.112	ISDN vocabulary and the basic meaning of teleservice terms
CCITT Recommendation I.221	Definitions for busy conditions and related call states
ETS 300 144	64 kbit/s frame structure, inband signalling, and sub-channel structure
ETS 300 111	Telephony 3,1 kHz service description used for fallback and audio behaviour
ETS 300 263	Telephony 7 kHz service description used for fallback and terminal support
CCITT Recommendation G.711	3,1 kHz speech coding
CCITT Recommendation G.722	7 kHz speech coding
CCITT Recommendation G.728	Optional low-delay speech coding
ETS 300 143	Inband signalling procedures for audiovisual terminals
ITU-T Recommendations T.122, T.124, T.123, T.125	Multipoint communication, generic conference control, protocol stacks, and multipoint transport
ETS 300 483	Main functionalities and basic requirements for MCUs
ETS 300 345	Interworking between public ISDNs and private ISDNs
ITU-T Recommendations H.242 and H.243	Establishing audiovisual communication and chair control in multipoint conferences
CCITT Recommendation I.140	Attribute technique used to describe ISDN services
ETS 300 011, ETS 300 012, ETS 300 403-1, ETS 300 402-1, ETS 300 267-1	Basic and primary rate layer 1, and DSS1 signalling layer specifications

What does the SIST ETS 300 675 E1:2003 document contain?

SIST ETS 300 675 E1:2003 contains the service description, operating procedures, interworking rules, and attribute mappings for the audiographic conference teleservice. It also includes the tables that describe subscription limits, low-layer and access attributes, and high-layer protocol functions for Call 1 and later calls.

Annex A gives a system view of how the supporting standards fit together, which helps when designing protocol stacks or checking compatibility. Annex B summarizes which supplementary services can apply in the audiographic conference context, and Annex C lists related documents for background reading and implementation work.

SLOVENSKI STANDARD
01-december-2003
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Integrated Services Digital Network (ISDN); Audiographic conference teleservice;
Service description
Ta slovenski standard je istoveten z: ETS 300 675 Edition 1
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
33.160.60 9HþSUHGVWDYQLPXOWLPHGLMVNL Multimedia systems and
VLVWHPLLQRSUHPD]D teleconferencing equipment
WHOHNRQIHUHQFH
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 675
TELECOMMUNICATION November 1996
STANDARD
Source: ETSI TC-TE Reference: DE/TE-04031
ICS: 33.080
Key words: Audiographic, conference, inband, ISDN, stage 1
Integrated Services Digital Network (ISDN);
Audiographic conference teleservice;
Service description
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: [e-mail]
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1996. All rights reserved.

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ETS 300 675: November 1996
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 675: November 1996
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions.9
4 Abbreviations.10
5 Description .10
5.1 General description.10
5.2 Basic facilities .10
5.2.1 Audio facilities .10
5.2.2 Conference control facility .11
5.2.3 Data transmission facility.11
5.2.4 Graphics facility .11
5.3 Other facilities .11
6 Procedures.11
6.1 Provision and withdrawal .11
6.2 Normal procedures .12
6.2.1 Originating the call (call establishment).12
6.2.2 Indications during call establishment.13
6.2.3 Terminating the conference .13
6.2.3.1 Point-to-point conference .13
6.2.3.2 Multipoint conference.13
6.2.4 Change of communication mode .13
6.2.5 Multipoint control .14
6.2.6 Data communication .14
6.3 Exceptional procedures .14
6.3.1 Situations at the calling user side.14
6.3.2 Situations at the called user side.14
6.3.3 Situations due to network conditions.15
6.3.4 Retention of call information.15
7 Intercommunication and interworking considerations .15
7.1 Fall-back procedures .15
7.1.1 Fall-back to the telephony 3,1 kHz teleservice.15
7.1.1.1 Procedures .15
7.1.1.2 Interworking with non-ISDNs .16
7.1.2 Fall-back to the telephony 7 kHz teleservice.16
7.2 Interworking with private ISDNs.16
7.3 Restricted network operation .16
8 Interaction with other supplementary services .16
9 Static description of the service using attributes .17
9.1 Low layer attributes.17
9.2 Access attributes .17
9.3 High layer attributes .18
9.4 General attributes .18
Annex A (informative): Relation between standards and recommendations relevant for the
audiographic conference service.19

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ETS 300 675: November 1996
Annex B (informative): Applicability of supplementary services to the audiographic conference
teleservice. 20
B.1 General. 20
B.2 Audiographic conference based on one circuit-mode 64 kbit/s connection . 20
B.3 Audiographic conference based on two or more circuit-mode 64 kbit/s connections. 21
Annex C (informative): Bibliography . 22
History. 23

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ETS 300 675: November 1996
Foreword
This European Telecommunication Standard (ETS) has been produced by the Terminal Equipment (TE)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
Transposition dates
Date of adoption of this ETS: 25 October 1996
Date of latest announcement of this ETS (doa): 28 February 1997
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 August 1997
Date of withdrawal of any conflicting National Standard (dow): 31 August 1997

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ETS 300 675: November 1996
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ETS 300 675: November 1996
1 Scope
This European Telecommunication Standard (ETS) defines the stage one of the audiographic conference
teleservice for the pan-European Integrated Services Digital Network (ISDN) as provided by European
public telecommunications operators. Stage one is an overall service description from the user's point of
view (see CCITT Recommendation I.130 in annex C), but does not deal with the details of the human
interface itself.
This ETS defines the interworking requirements of private ISDNs with the public ISDN.
In addition, this ETS specifies the base functionality where the service is provided to the user via a private
ISDN.
This ETS does not specify the additional requirements where the service is provided to the user via a
telecommunications network that is not an ISDN but does include interworking requirements of other
networks with the public ISDN.
Charging principles are outside the scope of this ETS.
The values of the general attributes are outside the scope of this ETS.
The audiographic conference teleservice is a real-time teleservice in which high quality speech, control
signals and data are interchanged using one or more circuit-mode 64 kbit/s connection(s).
This ETS is applicable to the stage two and stage three standards for the ISDN audiographic conference
teleservice. The terms "stage two" and "stage three" are also defined in CCITT Recommendation I.130.
Where the text indicates the status of a requirement (i.e. as strict command or prohibition, as authorization
leaving freedom, or as a capability or possibility), this will be reflected in the text of the relevant stage two
and stage three standards.
Furthermore, conformance to this ETS is met by conforming to the stage three standard with the field of
application appropriate to the equipment being implemented concerning characteristics at the
user-network interface, and by conforming to the ETS on the end-to-end characteristics appropriate to the
equipment being implemented. Therefore, no method of testing is provided for this ETS.
NOTE: In the current version of this ETS the use of protocols in the ITU-T T.120 series of
recommendations (see annex C) is an option. This position may be reviewed later.
2 Normative references
This ETS incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to, or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies.
[1] CCITT Recommendation I.112 (1985)88): "Vocabulary of terms for ISDNs".
[2] CCITT Recommendation I.221 (1985)88): "Common specific characteristics of
services".
[3] ETS 300 144 (1996): "Integrated Services Digital Network (ISDN); Audiovisual
services; Frame structure for a 64 kbit/s to 1 920 kbit/s channel and associated
syntax for inband signalling".
[4] ETS 300 111 (1992): "Integrated Services Digital Network (ISDN); Telephony
3,1 kHz teleservice, Service description".
[5] ETS 300 263 (1994): "Integrated Services Digital Network (ISDN); Telephony
7 kHz teleservice, Service description".

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ETS 300 675: November 1996
[6] CCITT Recommendation G.728 (1992): "Coding of speech at 16 kbit/s using
low-delay code-excited linear prediction".
[7] ETS 300 143 (1994): "Integrated Services Digital Network (ISDN): Audiovisual
services; Inband signalling procedures for audiovisual terminals using digital
channels up to 2 048 kbit/s".
[8] ITU-T Recommendation T.122 (1985)93): "Multipoint communication service for
audiographics and audiovisual conferencing service definition".
[9] ITU-T Recommendation T.124 (1995): "Generic conference control".
[10] ITU-T Recommendation T.123 (1985)94): "Protocol stacks for audiographic and
audiovisual teleconference applications".
[11] CCITT Recommendation G.711 (1985)88): "Pulse code modulation (PCM) of
voice frequencies".
[12] CCITT Recommendation G.722 (1985)88): "7 kHz audio-coding within
64 kbit/s".
[13] ETS 300 483 (1996): "Terminal Equipment (TE); Integrated Services Digital
Network (ISDN); Multipoint communication for audiovisual services; Main
functionalities and basic requirements for Multipoint Control Units (MCUs)".
[14] ETS 300 345 (1995): "Integrated Services Digital Network (ISDN): Interworking
between public ISDNs and private ISDNs for the provision of telecommunication
services. General aspects".
[15] ITU-T Recommendation H.242 (1985)96): "System for establishing
communication between audiovisual terminals using digital channels up to
1 920 kbit/s".
[16] CCITT Recommendation I.140 (1985)88): "Attribute technique for the
characterization of telecommunication services supported by an ISDN and
network capabilities of an ISDN".
[17] ETS 300 011 (1992): "Integrated Services Digital Network (ISDN); Primary rate
user-network interface, Layer 1 specification and test principles".
[18] ETS 300 012 (1992): "Integrated Services Digital Network (ISDN); Basic
user-network interface, Layer 1 specification and test principles".
[19] ETS 300 403-1 (1995): "Integrated Services Digital Network (ISDN); Digital
Subscriber Signalling System No. one (DSS1) protocol; Signalling network layer
for circuit-mode basic call control; Part 1: Protocol specification
(ITU-T Recommendation Q.931 (1993), modified)".
[20] ETS 300 402-1 (1995): "Integrated Services Digital Network (ISDN); Digital
Subscriber Signalling System No. one (DSS1) protocol; Data link layer;
Part 1: General aspects (ITU-T Recommendation Q.920 (1993), modified)".
[21] ETS 300 267-1 (1994): "Integrated Services Digital Network (ISDN); Telephony
7 kHz and videotelephony teleservices Digital Subscriber Signalling System No.
one (DSS1) protocol; Part 1: Protocol specification".
[22] ITU-T Recommendation H.243 (1985)93): "Procedures for establishing
communication between three or more audiovisual terminals using digital
channels up to 1920 kbit/s".
[23] ITU-T Recommendation T.125 (1994): "Multipoint communication service
protocol specification".
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ETS 300 675: November 1996
3 Definitions
For the purposes of this ETS, the following definitions apply:
Integrated Services Digital Network (ISDN): An integrated services network that provides digital
connections between user-network interfaces (CCITT Recommendation I.112 [1], subclause 2.3,
definition 308).
restricted network: A network consisting of multiples of 64 kbit/s links, but where only multiples of
56 kbit/s are usable for the terminals.
service; telecommunications service: That which is offered by a service provider to its customers in
order to satisfy a specific telecommunication requirement (CCITT Recommendation I.112 [1],
subclause 2.2, definition 201).
NOTE: Bearer service and teleservice are types of telecommunication service. Other types of
telecommunication service may be identified in the future.
supplementary service: A service which modifies or supplements a basic telecommunication service.
Consequently, it cannot be offered to a customer as a standalone service. It needs to be offered together
with or in association with a basic telecommunication service. The same supplementary service may be
common to a number of telecommunication services (based on CCITT Recommendation I.210,
subclause 2.4).
teleservice: A type of telecommunication service that provides the complete capability, including terminal
equipment functions, for communication between users according to protocols established by agreement
between service providers (CCITT Recommendation I.112 [1], subclause 2.2, definition 203).
audiographic conference terminal: A terminal that supports the audiographic conference teleservice.
7 khz terminal: A terminal that supports the telephony 7 kHz teleservice.
3,1 khz terminal: A terminal that supports only the telephony 3,1 kHz teleservice.
videotelephone terminal: A terminal that supports the videotelephony teleservice.
fall-back: The mechanism whereby the request for the audiographic conference service, which includes
an indication that an alternative teleservice is acceptable, results in a call using the alternative teleservice.
In the case of the audiographic conference teleservice, the alternative teleservices are the telephony
7 kHz or the telephony 3,1 kHz teleservices.
served user: A user to whom the audiographic conference teleservice is provided.
network determined user busy: As described in CCITT Recommendation I.221 [2], subclause 2.1.4.
user determined user busy: As described in CCITT Recommendation I.221 [2], subclause 2.1.4.
retention timer: This timer specifies the amount of time that the network retains all the call information
supplied by the calling user when the call encounters busy or is terminated. Implementation of this timer is
a network option. The value for this timer shall be greater than 15 seconds.
Multipoint Control Unit (MCU): A piece of equipment located in a node of the network or in a terminal
that connects several terminals and, according to certain criteria, processes audiovisual signals and
distributes them to the connected terminals.
sub-channel: Each bit position of the byte of a 64 kbit/s channel as defined in ETS 300 144 [3].
service channel: The eight sub-channels of a 64 kbit/s channel as defined in ETS 300 144 [3].
Multi Layer Protocols (MLP): As defined in the ITU-T T.120 series of recommendations.

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ETS 300 675: November 1996
ISDN number: A number conforming to the numbering plan and structure specified in
CCITT Recommendation E 164.
4 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
ISDN Integrated Services Digital Network
MCS Multipoint Communication Service
MCU Multipoint Control Unit
MLP Multi Layer Protocols
PSTN Public Switched Telephone Network
5 Description
5.1 General description
The audiographic conference teleservice is a real-time teleservice in which speech is transmitted together
with signals for conference control and data communication between a terminal and a Multipoint Control
Unit (MCU) or between two terminals by means of one or more 64 kbit/s circuit-mode connections in the
ISDN.
The audiographic conference teleservice comprises two cases:
- case a): audiographic conference based on using one circuit-mode 64 kbit/s connection; and
- case b): audiographic conference based on using two or more circuit-mode 64 kbit/s connections.
An audiographic conference terminal shall be capable of supporting the telephony 3,1 kHz teleservice as
described in ETS 300 111 [4] and the telephony 7 kHz teleservice as described in ETS 300 263 [5]. To
improve the data communication capacity, the encoding specified in CCITT Recommendation G.728 [6]
may be implemented as an option.
The audiographic conference teleservice shall allow communication between:
- two users (e.g. terminals) in a point-to-point configuration via the ISDN over a B-channel;
- three or more users in a multipoint configuration.
User information and user-to-user signalling shall be transferred over the B-channel. User-network
signalling shall be provided over the D-channel.
A Multipoint Control Unit (MCU), to which all locations are connected individually over the ISDN, is
required for the interconnection of three or more users in a multipoint configuration. Two or more MCUs
may be interconnected to increase the number of participants of a multipoint conference.
The network provides tones and/or announcements to support this teleservice. Tones and/or
announcements can be used to indicate the progress (or lack of progress) of a call. The application and
meaning of the tones and announcements are a national matter and outside the scope of this ETS.
A description of the relation between the different elements described in this ETS can be found in
annex A.
5.2 Basic facilities
5.2.1 Audio facilities
The audio system shall be designed to offer handsfree communication to two or more participants at each
site. The participants should be allowed to listen and speak simultaneously. The speech transmission
bandwidth shall nominally be 7 kHz, although this may be reduced when the conference has been opened
to participants served by a non-ISDN network.

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ETS 300 675: November 1996
5.2.2 Conference control facility
A conference control system for governing call establishment and call termination, controlling conference
modes and audio/image signals; and for transmission of conference control signals (e.g. floor requests,
tokens), shall be provided.
The conference control system shall, as a minimum, be based on the signals and procedures specified in
ETS 300 144 [3] and ETS 300 143 [7]. For improved performance the Multipoint Communication Service
(MCS) as described in ITU-T Recommendation T.122 [8] using the Generic Conference Control protocols
described in ITU-T Recommendation T.124 [9] can be used.
5.2.3 Data transmission facility
A data transmission facility shall be provided. The facility shall be based on data channels as defined in
ETS 300 144 [3]. For improved performance the protocol stack defined in ITU-T Recommendation
T.123 [10] should be implemented.
5.2.4 Graphics facility
The graphics system shall be designed to transmit documents, charts, diagrams, etc., during the
conference.
NOTE: As a minimum, a facsimile group 3 transmission in a separate B-channel should be
available.
5.3 Other facilities
As options, other facilities can be provided as applications using the MCS specified in
ITU-T Recommendation T.122 [8]. Examples are:
- still picture;
NOTE 1: ITU-T Recommendation T.126 specifies a Multipoint still image and annotation
protocol.
- file transfer.
NOTE 2: ITU-T Recommendation T.127 specifies a Multipoint binary file transfer protocol.
6 Procedures
6.1 Provision and withdrawal
The audiographic conference shall either be provided after prior arrangement with the service provider, or
shall be generally available.
NOTE: As a service provider option, the audiographic conference teleservice can be offered
with several subscription options which apply separately to each ISDN number, or
groups of ISDN numbers on the interface. For each subscription option, only one value
can be selected.
It should be noted that in this context an interface may consist of a group of physical
interfaces.
Subscription options for the interface are summarized in table 1.

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ETS 300 675: November 1996
Table 1
Subscription option Value
Maximum number of information m: where m is not greater than the number
channels available of information channels on the interface.
Maximum number of total calls n: where n is not greater than the number of
present information channels on the interface.
The user can be identified by an ISDN number or a group o
...