SIST ETS 300 678 E1:2003

• Abstract:

  To prepare a stage one service description for a videoconference 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 300 678 ed.1 (1996-11) - Integrated Services Digital Network (ISDN); Videoconference teleservice; Service description

SIST ETS 300 678 E1:2003 is the Slovenian adoption of ETS 300 678 Edition 1 from ETSI, published by SIST. It specifies the stage one service description for the Integrated Services Digital Network (ISDN) videoconference teleservice, so it tells service providers, network operators and terminal implementers how the service works from the user point of view.

The document covers the call model, interworking, supplementary services, service attributes and optional encryption for ISDN videoconferencing. It is the service-level description that later stage standards build on.

What does SIST ETS 300 678 E1:2003 specify?

SIST ETS 300 678 E1:2003 defines the stage one description of the videoconference teleservice in the pan-European ISDN as provided by public telecommunications operators. It describes point-to-point service between two terminals or between one terminal and a Multipoint Control Unit (MCU), and it also sets the interworking rules for private ISDNs.

The standard is organized into clauses 1 to 10, followed by informative annexes A to D.

Annex	What it covers
Annex A	Overall videoconference service functions, configurations and conference set-up modes
Annex B	Applicability of supplementary services
Annex C	Relationship between standards and recommendations relevant to the videoconference service
Annex D	Bibliography

The scope also makes clear that the MCU-based “conference service” itself is outside the standard’s scope, even though the MCU is part of the described teleservice environment. Charging principles and the values of the general attributes are also left outside the scope. The document is about service description, not about human-interface detail or test methods.

What are the key requirements of SIST ETS 300 678 E1:2003?

Service model and channel use

• Clause 5 says the videoconference teleservice is a real-time service that carries audio, video, control signals and data over two or more circuit-mode 64 kbit/s connections. In practice, implementers need to support multichannel ISDN calls rather than a single bearer connection.
• Clause 5 and clause 6 state that call 1 is established first, then additional calls are added. Call 1 is used initially for speech, while later calls carry video and data. This matters because terminals must negotiate the first channel before any wider conference bandwidth becomes available.
• Clause 5 says a MCU is required for three or more users in a multipoint configuration, and MCUs may be interconnected. For deployments, that means multiparty videoconferencing depends on MCU-capable infrastructure, not only on end terminals.

Provisioning, call control and failure handling

• Clause 6.1 allows the service to be provided by prior arrangement or as a generally available service, and it allows subscription options such as the maximum number of information channels and total calls. Operators use this to cap service use per ISDN number or per interface group.
• Clause 6.2 describes call establishment, progress indications, varying the number of B-channels during a conference, and termination. Users should receive progress indications, and the network must provide tones and/or announcements to show whether the call is moving forward.
• Clause 6.3 covers exceptional cases such as invalid ISDN numbers, busy called users, network congestion and the failure of additional calls. In practice, terminals and networks must give clear failure indications and help the user decide whether to retry with fewer channels or clear the attempt.
• Clause 6.3.4 introduces retention of call information as a network option when the call meets busy or congestion conditions. That means the network may keep the dialed information for a limited time so the user does not need to re-enter it immediately.

Interworking, mode changes and special services

• Clause 7 sets the interworking rules with videotelephony, audiographic terminals, non-ISDNs, private ISDNs and restricted networks. The standard requires fallback to the telephony 3,1 kHz teleservice when allowed, so users can still complete a call when videoconference service cannot be maintained end to end.
• Clause 7.4 requires terminals to interoperate with restricted networks that use 56 kbit/s or multiples of 64 kbit/s with a ones density restriction. Implementers need the H.242 procedures named there, or restricted-network calls will not work correctly.
• Clause 8 explains how supplementary services interact with inband signalling. If a supplementary service interrupts the inband path, the terminals must revert to mode 0, and the network must show an appropriate B-channel condition. This matters for hold, portability and similar services that can disturb the conference channel structure.
• Clause 10 makes encryption optional but defines how to use it when implemented, including the Encryption Control Signal channel, ETS 300 143 procedures and ITU-T Recommendation H.233. For general use in Europe, the document recommends that supported algorithms include BARAS and that key management include Diffie-Hellman or RSA.

What terms does SIST ETS 300 678 E1:2003 define?

• Integrated Services Digital Network (ISDN) - An integrated services network that provides digital connections between user-network interfaces.
• Channel Aggregation Unit (CAU) - Equipment with multiple 64 kbit/s accesses and one higher-bit-rate access, used to aggregate channels for terminals.
• Multipoint Control Unit (MCU) - Equipment that connects several terminals and processes/distributes audiovisual signals for multipoint conferencing.
• teleservice - A telecommunications service that includes terminal functions and works according to agreed protocols between service providers.
• fall-back - The mechanism that redirects a videoconference attempt to an alternative service, usually telephony 3,1 kHz, when allowed.
• Network Determined User Busy (NDUB) - A case where the network determines that the called user is busy.
• User Determined User Busy (UDUB) - A case where the user-side response indicates busy status even though the network offered the call.

Who uses SIST ETS 300 678 E1:2003?

SIST ETS 300 678 E1:2003 is used by ISDN service providers, network operators, terminal manufacturers and MCU vendors. It is also relevant to system integrators and planners who need to decide how videoconference calls are set up, how many channels are used, and how fallback works when the full service is not available.

Quality and interoperability teams use it to check that terminals and networks handle call establishment, busy conditions, restricted networks, supplementary services and optional encryption in a consistent way. It is especially useful when a product must work across public ISDN, private ISDN and mixed-network environments.

Which standards are used with SIST ETS 300 678 E1:2003?

The normative references in clause 2 provide the mechanisms that the service description depends on.

• ETS 300 144 - Defines audiovisual frame structure, inband signalling and the Encryption Control Signal channel used by the service.
• ETS 300 143 - Gives inband signalling procedures for audiovisual terminals and is used for call control and mode handling.
• ETS 300 111 and ETS 300 263 - Define the telephony 3,1 kHz and telephony 7 kHz teleservices used for fallback and compatibility.
• ETS 300 483 - Defines main functionalities and basic requirements for MCUs.
• ETS 300 345 - Covers interworking between public and private ISDNs.
• ITU-T H.242, H.243 and H.233 - Support audiovisual call establishment, multipoint procedures and confidentiality.
• ITU-T T.120 series - Provides data and conference-control protocols for multipoint communication.
• ITU-T H.261 - Supplies the video codec referenced for audiovisual operation.
• ITU-T I.140 and I.130 - Provide the attribute technique and service-characterization method used to describe the service.

What does the SIST ETS 300 678 E1:2003 document contain?

SIST ETS 300 678 E1:2003 contains the service scope, definitions, abbreviations, procedures and the static attribute description for ISDN videoconferencing. Clause 6 describes provisioning, normal call handling, exceptional situations and retention of call information, while clause 7 covers intercommunication, fallback and interworking cases. Clause 8 explains how supplementary services affect inband signalling, and clause 10 covers optional encryption.

The annexes add practical context: Annex A describes point-to-point, switched multipoint and picture-composition multipoint configurations; Annex B groups supplementary services by applicability; Annex C shows how the related protocol stack fits together; and Annex D lists background references. The document also includes tables for low-layer, access and high-layer attributes, which are the main reference point for implementers checking service behavior across the ISDN layers.

SLOVENSKI STANDARD
01-december-2003
Digitalno omrežje z integriranimi storitvami (ISDN) – Daljinske storitve:
Videokonferenca – Opis storitve
Integrated Services Digital Network (ISDN); Videoconference teleservice; Service
description
Ta slovenski standard je istoveten z: ETS 300 678 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 300 678
TELECOMMUNICATION November 1996
STANDARD
Source: ETSI TC-TE Reference: DE/TE-04030
ICS: 33.080
Key words: Conference, ISDN, stage 1, video
Integrated Services Digital Network (ISDN);
Videoconference 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 300 678: 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 300 678: November 1996
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions.8
4 Abbreviations.10
5 Description .10
6 Procedures.10
6.1 Provision and withdrawal .10
6.2 Normal procedures .11
6.2.1 Originating the call (call establishment).11
6.2.2 Indications during call establishment.12
6.2.3 Varying the B-channel number during the conference.12
6.2.4 Terminating the conference .12
6.2.4.1 Point-to-point conference .12
6.2.4.2 Multipoint conference.12
6.2.5 Change of communication mode .12
6.2.6 Multipoint control .13
6.2.7 Data communication .13
6.3 Exceptional procedures .13
6.3.1 Situations at the calling user side.13
6.3.2 Situations at the called user side.13
6.3.3 Situations due to network conditions.13
6.3.4 Retention of call information.13
6.3.5 Failure of additional calls.14
7 Intercommunication and interworking .14
7.1 Normal operation .14
7.2 Fall-back procedures .14
7.2.1 Fall-back to the telephony 3,1 kHz teleservice.14
7.2.2 Interworking with non-ISDNs.15
7.3 Interworking with private ISDNs.15
7.4 Restricted network operation .15
8 Special use of supplementary services.15
9 Static description of the service using attributes .16
9.1 Low layer attributes.16
9.2 Access attributes .16
9.3 High layer attributes .17
9.4 General attributes .17
10 Encryption.18
Annex A (informative): Various functionalities of the complete "videoconference service" .19
A.1 Overall description.19
A.2 Videoconference configurations.19
A.2.1 Point-to-point configuration.19
A.2.2 Switched video multipoint configuration.20

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ETS 300 678: November 1996
A.2.3 Multipoint configuration with picture composition. 20
A.3 Conference set-up mode. 21
Annex B (informative): Applicability of supplementary services to the videoconference teleservice. 22
B.1 Hold, Transfer and Portability . 22
B.2 Multiparty supplementary services . 22
B.3 Supplementary services applicable without restriction . 22
B.4 Supplementary services applicable with restriction . 22
Annex C (informative): Relation between standards and recommendations relevant for the
videoconference service . 24
Annex D (informative): Bibliography . 25
History. 27

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ETS 300 678: 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 300 678: November 1996
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ETS 300 678: November 1996
1 Scope
This European Telecommunication Standard (ETS) defines the stage one of the videoconference
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 D), but does not deal with the details of the human
interface itself.
The videoconference teleservice applies to point-to-point communications established between either two
terminals or one terminal and a Multipoint Control Unit (MCU).
The "conference service" provided by a MCU is outside the scope of this ETS. Related information may be
found in informative annexes A and B of this ETS, and also in ITU-T Recommendation F.730 (see
annex D).
This ETS defines the interworking requirements of private ISDNs with the public ISDN.
In addition, this ETS specifies the base requirements 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 videoconference teleservice is a real-time teleservice in which high quality audio, video, control
signals and data are interchanged using two or more circuit-mode 64 kbit/s connections.
This ETS is applicable to the stage two and stage three standards for the ISDN videoconference
teleservice. The terms "stage two" and "stage three" are also defined in CCITT Recommendation I.130
(see annex D). 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 is 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 standard on the end-to-end characteristics appropriate to the
equipment being implemented. Therefore, no method of testing is provided for this ETS.
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] 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".
[2] ETS 300 111 (1992): "Integrated Services Digital Network (ISDN); Telephony
3,1 kHz teleservice, Service description".
[3] ETS 300 263 (1994): "Integrated Services Digital Network (ISDN); Telephony
7 kHz teleservice, Service description".
[4] CCITT Recommendation G.728 (1992): "Coding of speech at 16 kbit/s using
low-delay code excited linear prediction".

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ETS 300 678: November 1996
[5] 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".
[6] CCITT Recommendation G.711 (1985)88): "Pulse code modulation (PCM) of
voice frequencies".
[7] CCITT Recommendation G.722 (1985)88): "7 kHz audio-coding within
64 kbit/s".
[8] ITU-T Recommendation I.140 (1985)93): "Attribute technique for the
characterization of telecommunication services supported by an ISDN and
network capabilities of an ISDN".
[9] ETS 300 483 (1996): "Terminal Equipment (TE); Integrated Services Digital
Network (ISDN); Multipoint communications for Audiovisual Services; Main
functionalities and basic requirements for Multipoint Control Units (MCUs)".
[10] ITU-T Recommendation H.242 (19985)96): "System for establishing
communication between audiovisual terminals using digital channels up to
2 Mbit/s".
[11] ITU-T Recommendation H.233: "Confidentiality system for audiovisual services".
[12] ITU-T Recommendation H.243 (1985)93): "Procedures for establishing
communication between three or more for audiovisual terminals using digital
channels up to 1 920 kbit/s".
[13] ETS 300 345: "Integrated Services Digital Network (ISDN); Interworking
between public ISDNs and private ISDNs for the provision of telecommunication
services. General aspects".
[14] ITU-T Recommendation T.122 (1985)93): "Multipoint communication service for
audiographics and audiovisual conferencing service definition".
[15] ITU-T Recommendation T.123 (1985)94): "Protocol stacks for audiographic and
audiovisual teleconference applications".
[16] ITU-T Recommendation T.124 (1995): "Generic conference control".
[17] ITU-T Recommendation T.125 (1994): "Multipoint communication service
protocol specification".
[18] ITU-T Recommendation T.126: "Multipoint still image and annotation protocol".
[19] ITU-T Recommendation T.127: "Multipoint binary file transfer protocol".
[20] ITU-T Recommendation H.261: "Video codec for audiovisual services at
p x 64 kbit/s".
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 (ITU-T Recommendation I.112, subclause 2.3,
definition 308).
Channel Aggregation Unit (CAU): A device having both multiple 64 kbit/s accesses and a single access
at a higher bitrate. Reference in this ETS to "CAU" or "aggregator" means equipment conforming to
ETS 300 481 (cf. bibliography in annex D).

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ETS 300 678: November 1996
service; telecommunications service: That which is offered by a service provider to its customers in
order to satisfy a specific telecommunication requirement [ITU-T Recommendation I.112, subclause 2.2,
definition 201].
supplementary service: A supplementary service modifies or supplements a basic telecommunication
service. Consequently, it cannot be offered to a customer as a standalone service. It should 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 [ITU-T 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 [ITU-T Recommendation I.112, subclause 2.2, definition 203].
videoconference terminal: A terminal that supports the videoconference 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 videoconference teleservice, which includes an
indication that an alternative teleservice is acceptable, results in a call using the alternative teleservice. In
the case of the videoconference teleservice, the alternative teleservice is the telephony 3,1 kHz
teleservice. However, at the called side fall-back might result to the telephony 7 kHz teleservice.
served user: A user to whom the videoconference teleservice is provided.
Network Determined User Busy (NDUB): See description given in subclause 2.1.4 of
ITU-T Recommendation I.221.
User Determined User Busy (UDUB): Is specified for the case where the network offers the call to the
user and if no compatible terminal responds "positively" but one or more compatible terminals respond
"user busy".
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 (ETS 300 144 [1]).
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 is 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 criterion, processes audiovisual signals and
distributes them to the connected terminals. Its main functionalities and applicable requirements are
specified in ETS 300 483 [9].
Service Channel (SC): The eighth sub-channel of a 64 kbit/s channel, or the seventh sub-channel when
communicating in restricted mode (ETS 300 144 [1]).
multi layer protocols: As defined in the T.120 series of ITU-T recommendations.
ISDN number: A number conforming to the numbering plan and structure specified in
CCITT Recommendation E.164.
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4 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
BARAS Baseline Algorithm Recommended for use in Audiovisual Systems
CAU Channel Aggregation Unit
CIF Common Intermediate Format
ISDN Integrated Services Digital Network
MCS Multipoint Communication Service
MCU Multipoint Control Unit
MLP Multi Layer Protocols
MSN Multiple Subscriber Number
NDUB Network Determined User Busy
PSTN Public Switched Telephone Network
QCIF Quarter Common Interface Format
TE Terminal Equipment
UDUB User Determined User Busy
5 Description
The videoconference teleservice is a real-time teleservice in which audio and video signals are
transmitted inband together with signals for conference control and data communication, between a
terminal and a MCU, or between two terminals by means of two or more (up to 30) 64 kbit/s circuit-mode
connections in the ISDN.
NOTE 1: The quality of the moving colour pictures of the participants rises quickly with the
number of the 64 kbit/s connections.
NOTE 2: A videoconference terminal may support, as options, the telephony 3,1 kHz teleservice
as described in ETS 300 111 [2] and the telephony 7 kHz teleservice as described in
ETS 300 263 [3].
NOTE 3: To improve the video and data communication capacity, the audio encoding specified
in CCITT Recommendation G.728 [4] may be implemented as an option.
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.
User information and end-to-end signalling shall be transferred over the B-channel. Signalling for call
control shall be provided over the D-channel.
A 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.
6 Procedures
6.1 Provision and withdrawal
The videoconference teleservice shall either be provided after prior arrangement with the service provider,
or shall be generally available.
NOTE 1: As a service provider option, the videoconference 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.
Subscription options for the interface are summarized in table 1.

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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
NOTE 2: The physical interface may be one, several, or a combination of basic and primary rate
access(es). A Channel Aggregation Unit (CAU) may be used to allow connection of
single access terminals. It should be noted that in this context an interface may consist
of a group of physical interfaces.
The user can be identified by an ISDN number, a group of ISDN numbers, or globally
for all ISDN numbers on the interface.
More than one ISDN number can be associated with the interface as a part of a
supplementary service such as the Multiple Subscriber Number (MSN) supplementary
service. In the case of one ISDN number, the option given in table 1 for the number of
calls can only exceed the number of information channels in association with a
supplementary service (e.g. the call waiting supplementary service). As a network
provider option, separate values may be specified for incoming and for outgoing calls
for either or both of the limits.
The videoconference teleservice shall be withdrawn by the service provider upon the
request of the subscriber, or for service reasons.
6.2 Normal procedures
For the videoconference teleservice, communication is by means of two or more 64 kbit/s connections,
and so two or more calls shall be established. For the establishment of the first call, the procedures of
subclause 6.2.1 shall apply. The subsequent calls shall be established using the procedures given in
subclause 6.2.1, provided that the first call has already been established.
The network shall provide out of band indications to indicate call progress. Network generated tones
and/or announcements shall be provided for the videoconference teleservice.
6.2.1 Originating the call (call establishment)
The videoconference teleservice shall be originated by the originating user:
- activating the terminal;
- performing the service selection, if applicable for the originating terminal; and
- terminating selection.
During this process, the originating user shall be given the appropriate indications as to the state of the
call.
The end-to-end path is framed according to ETS 300 144 [1]. The inband protocol shall be established
according to ETS 300 143 [5].
Call 1 shall be established before initiating any additional call.
NOTE 1: Call 1 is initially devoted to transfer of speech. The transmission audio mode on the
end-to-end digital path is defined according to ETS 300 144 [1], using the procedures
defined in ETS 300 143 [5].
Audio tones provided to the user during Call 1 shall be as for the telephony 3,1 kHz teleservice, given in
ETS 300 111 [2].
The subsequent calls can only be originated by the calling user's terminal after the connection has been
established on Call 1 and after the end-to-end capability exchange and mode initialization procedure are
completed.
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ETS 300 678: November 1996
NOTE 2: The subsequent calls are devoted to video and data communication.
6.2.2 Indications during call establishment
At the called side, the calls shall be accepted after successful checking of compatibility information by the
terminal(s) addressed.
After initiating Call 1 the calling user shall receive an acknowledgement that the network is able to process
the call. The called user shall receive an indication of the arrival of an incoming videoconference call. The
calling user shall also be given an indication that the call is being offered to the called user. Acceptance of
Call 1 by the called user (answer), shall cause the indications to be removed and the bi-directional
communication path to be provided.
After initiating each subsequent call, the calling user shall receive an acknowledgement that the network is
able to process the call. The called user shall receive an indication of the arrival of every additional
incoming videoconference call. Originating address (when available) and additional channel identification
number shall be used to check compatibility between successive incoming calls.
The acceptance of the subsequent calls by the called user (answer), shall cause the bi-directional
communication path to be provided.
6.2.3 Varying the B-channel number during the conference
The user (or MCU) can vary the number of connections during the conference. Set-up and release of
additional channels use the standard D-channel procedures. However the change of multiplex structure
shall be prepared by preliminary appropriate inband signalling procedures.
6.2.4 Terminating the conference
6.2.4.1 Point-to-point conference
A request to terminate the videoconference teleservice can be generated by either of the users. If one
user terminates the service, the other user(s) shall be given an appropriate indication.
6.2.4.2 Multipoint conference
A request to terminate the call(s) can be generated by either the user or the MCU controlled by the MCU
director or the user given the Chair control described in ITU-T Recommendation H.243 [12]. If one user
terminates his call to the MCU, the other user(s) shall be given an appropriate indication.
The termination of the whole conference shall be controlled by the MCU or by the user given the Chair
control.
NOTE: An MCU could be designed to establish the call to a given user if this connection is
unintentionally released.
6.2.5 Change of communication mode
Because of end-to-end integrity on the videoconference teleservice, different communication modes can
be used according to ETS 300 143 [5].
The audio mode used at call set-up is:
- 3,1 kHz speech (CCITT Recommendation G.711 [6]).
The normal operating mode is:
- 7 kHz speech (CCITT Recommendation G.722 [7]).
However, a video conference terminal should be able to support as an option:
- 3,1 kHz speech (CCITT Recommendation G.728 [4]).

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ETS 300 678: November 1996
The user (or MCU) can vary the audio mode during the communication.
The available bit rate is used by data and/or video signal for various picture definition (Common
Interchange Format (CIF), Quarter Common Interface
...