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IMPORT
R:\\ART\\W INTERNATIONAL TELECOMMUNICATION UNION
MF\\ITU.WM
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t
CCITT F.710
THE INTERNATIONAL
TELEGRAPH AND TELEPHONE
CONSULTATIVE COMMITTEE
TELEMATIC, DATA TRANSMISSION
AND TELECONFERENCE SERVICES
OPERATIONS AND QUALITY OF SERVICE
GENERAL PRINCIPLES FOR AUDIOGRAPHIC
CONFERENCE SERVICE
Recommendation F.710
IMPORT Geneva, 1991
R:\\ART\\
WMF\\CCIT
TRUF.WMF
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Printed in Switzerland
FOREWORD
The CCITT (the International Telegraph and Telephone Consultative
Committee) is a permanent organ of the International Telecommunication Union
(ITU). CCITT is responsible for studying technical, operating and tariff
questions and issuing Recommendations on them with a view to standardizing
telecommunications on a worldwide basis.
The Plenary Assembly of CCITT which meets every four years, establishes
the topics for study and approves Recommendations prepared by its Study Groups.
The approval of Recommendations by the members of CCITT between Plenary
Assemblies is covered by the procedure laid down in CCITT Resolution No. 2
(Melbourne, 1988).
Recommendation F.710 was prepared by Study Group I and was approved under
the Resolution No. 2 procedure on the 11 of March 1991.
___________________
CCITT NOTE
In this Recommendation, the expression "Administration" is used for
conciseness to indicate both a telecommunication Administration and a recognized
private operating agency.
F ITU 1991
All rights reserved. No part of this publication may be reproduced or utilized in
any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the ITU.
PAGE BLANCHE
Recommendation F.710
Recommendation F.710
GENERAL PRINCIPLES FOR AUDIOGRAPHIC CONFERENCE SERVICES
1 Introduction
This Recommendation defines the rules to be followed in the international
audiographic conference (AGC) service. Specific infrastructure, terminal and
network aspects of the service are described in the AV.20 , AV.300 and AV.400-
Series of Recommendations.
2 Definition
The Audiographic Conference (AGC) service is an international service,
offered by Administrations, enabling participants to conduct a real-time
teleconference between users situated in different locations, connected by
terminals and telecommunications networks.
The AGC service is a type of Teleconference service (TCS) in which audio
signals are exchanged together with non-voice graphics information (data, text,
images, etc.) except for motion video.
The AGC service may utilize computer conference or other data storage
facilities when unique features provided by these facilities are required to
augment a real-time audiographic conference.
Unless otherwise noted, the terms and definitions relating to
teleconferencing used in this Recommendation are as defined in Annex B of
Recommendation F.701.
3 Description
3.1 General
The AGC service provides the necessary arrangement for a real-time
conference in which audio signals, together with graphics information, are
exchanged among individuals or groups of individuals at two or more locations
connected by means of a telecommunications network(s). A conference can be
established between personal terminals and other personal terminals, between
conference rooms and other conference rooms, or a combination of the two.
An essential characteristic of the AGC service is that it provides the
basic level of compatibility (see S 3.4) between all terminals participating in
the service. Optional service features may be added when required to serve
particular conferencing needs.
A Multipoint control unit (MCU), to which all locations are connected
individually, is required for the interconnection of terminal equipment used in
conferences involving three or more locations. The MCU provides proper
distribution of the various audiographic signals among the connected locations
and takes part in maintaining the proper procedures between the connected
terminals.
Two or more MCUs may be interconnected when required to extend the
conference to participants for which distance or other limitations preclude the
use of a single MCU.
Two important features for the AGC user are quality of sound and speed of
transmission of documents. When the overall bit rate is limited, these two
features may be alternately given preference by dynamic switching between audio
codecs controlled through H.221/AV.221 BAS codes in accordance with the
communications procedures defined in Recommendation H.242/AV.242.
styleref head_footRecommendation F.710PAG
E9
3.2 Service modes
There are two states for the Audiographic Conference service:
ù Main mode: An operational mode that supports full error detection and
correction in a point-to-point or multipoint graphics information
communications environment. Primary service requires, as a minimum, two
way communications between the MCU and each participant to achieve full
error detect and correct (EDC) operation;
ù Auxiliary mode: A distribution only mode of operation for networks
where two-way communication is either not available or not desirable
due to the large number of units involved. Receive only graphics
terminals may be developed to support the auxiliary mode only.
Provisions are made to permit combined operation of both states where some
units are broadcast receivers listening to other units utilizing two-way
operation.
3.3 Functional model
3.3.1 Participants
The model for AGC interaction implies an exchange of information between
four types of role players. These players are:
ù Conference convenor: One who summons participants to a meeting and
makes all necessary prior arrangements.
ù Presenter: One who controls the visual information being actively
discussed in the meeting.
ù Audience member: One who participates in an audiographic conference
other than the Presenter.
ù Conference conductor: One who leads or guides the technical management
of the audiographic conference.
Information exchanged between the players are of two types:
ù audio and graphics (imagery) information exchange;
ù conference establishment/release and control.
The roles of Presenter and Audience member may be interchanged any number
of times during the conduct of a given conference.
A single individual may act as both the Conference convenor and Conference
controller. Usually, this same individual will also act as a Presenter during the
course of the meeting.
3.3.2 Configuration
An example of the functional model is depicted in Figure 1/F.710. This
example may be expanded to include real-time access to a remote data base or
other file storage facility when required to satisfy a particular conference
requirement.
Figure 1/F.710 = 10 cm
3.4 Basic requirement
3.4.1 The general requirements of the AGC service are as follows:
a) A basic level of compatibility is provided between all terminals
participating in the AGC service, both nationally and internationally,
so that each may communicate audio, basic image and annotation ù coded
information to all other participants. This is to be achieved by
requiring that terminals comply with Recommendations AV.310 and AV.311.
b) It is for each Administration to decide on the network(s) which the AGC
service will be carried. There shall be no restriction on the type of
network to be used.
c) It should be possible to extend AGC service to any number of
Administrations.
d) To permit private use applications, for example encryption, there
should be no restrictions placed on the bit sequences used to transmit
audio and imagery information.
e) A received AGC image may be displayed, printed or recorded as decided
by the recipient and the characteristics of the receiving terminal.
f) It is essential that interworking be provided at least on an audio
basis.
g) The ability to control the conference from a single location is
required in a multipoint communications environment.
h) It is intended that the AGC service should require no fundamental
change to the Recommendations for existing services or networks.
PAGE10 styleref head_footRecommendation F.710
3.4.2 The AGC service is comprised of the following elements (audio is presumed
to be always available without interruption):
a) Establish conference: Call set up, conference establishment and
conference clearing at the network level.
b) Initiate image: Generation of an electronic image signal from a number
of common sources.
c) Coding/Compression: Reducing the amount of redundant data required to
represent the image.
d) Transmission: Conveying the information defining the image to other
terminals via a communications channel.
e) Display: Presenting the received or locally generated image signal
visually for conference purposes.
f) Protocol: Managing the network and terminal protocols in order to make
available, during the various AGC phases, the services required.
g) Image manipulation: Interactive manipulation of the image and
augmentation such as pointers, highlight and annotation (telewriting).
h) Multiplex: Combining the audio signal with the visual data when a
common channel is used for transmission.
i) Bridging: the ability to conference simultaneously among three or more
remote locations.
j) Control: actions initiated by the conference conductor to coordinate
and manage conference interaction between the various participants.
3.4.3 The following features apply to the AGC service:
a) Image input sources, such as:
ù paper/film (scanner);
ù electronic images (terminal resident, imported);
ù video capture (camera, VCR).
b) Graphics information in a variety of formats, such as:
ù digitized video (PAL, NTSC, RGB);
ù facsimile (G3, G4);
ù other document formats (raster, ODA/ODIF, structured);
ù videotex/teletex.
c) Conference configuration, such as:
ù add;
ù drop;
ù participation status.
Note ù Features are arbitrated as users are added to the conference.
3.4.4 In addition to the above basic requirements, the general features of the
Teleconferencing service (TCS) described in Recommendation F.701 also apply.
3.5 Standardized options
3.5.1 It is recognized that some conferences may need to communicate both
nationally and internationally using service features that are not included in
the basic requirements. A number of CCITT standardized options should, therefore,
be defined. However, the provision of any option in a service leads to some
degree of incompatibility and the number of standardized options should be
restricted, as shown below, to those features for which a clear international
need can be foreseen.
styleref head_footRecommendation F.710PAG
E9
3.5.2 The sending terminal shall ensure the transmission of documents using only
those options that have been indicated as being available at the receiving
terminal.
3.5.3 It shall be possible for more sophisticated terminals to provide
particular features different from the basic requirement (e.g. editing, autocall
setup, local view, etc.) in as far as these features do not affect the basic
service to other locations participating in the conference.
3.5.4 The standardized options should provide means for:
a) different pel transmission densities;
b) optional coding schemes;
c) grey scale images;
d) colour images;
e) printable areas;
f) escape into national and private options;
g) resolution conversion algorithms;
h) confidentiality/security;
i) document control and editing functions, such as:
ù document editing,
ù raster image editing (zoom, rotation, pan, scroll, etc.),
ù textual annotation (such as telewriting),
ù erase and go-back-one (undo),
ù help (local, suggested);
j) audio requirements, such as:
ù enhanced quality,
ù multiple speakers,
ù voice annotation/audio clips;
k) active participant indicators (speaker, presenter, etc.).
Note 1 ù The standardized options are negotiated during conference set-up.
Note 2 ù The standardized and nationally defined options should be used in
such a way as to minimize the need for the introduction of private use options.
Note 3 ù There is a need for further study as the service develops.
Changes may be required to this list.
4 Operational procedures
The AGC service is used for presenting the bi-level, grey scale and colour
visual materials with associated oral discussion in electronic "meetings" where
the locations linked by telecommunications can view and work on the same image
simultaneously.
PAGE10 styleref head_footRecommendation F.710
4.1 Sequence of operation
A meeting, using the AGC service, typically occurs in the following
sequence:
ù Reservation: The date and time of the proposed conference may be
coordinated by the Conference convenor.
ù Establish communications: Audio and graphics communications are
established to all locations participating in the conference at the
time and date agreed.
ù Originate an image: The initiating location transmits an image that is
simultaneously displayed at all other locations in the conference.
ù Work with the image: Once the image is displayed, any conference
location may activate an electronic pointer or annotate the image, with
all other locations immediately seeing the results of this action. All
changes and manipulations occur in real time.
ù Modify the image: The displayed image may be modified locally by
editing the processable form of the image. The resulting modifications,
when inserted into the conference, will immediately replace the current
display at all locations.
ù Record the image: Any user can record a copy of the image currently
displayed at any time without disrupting the meeting in progress. This
may be accomplished by printing on a hardcopy output device or by
storing on a magnetic disk.
ù Continue the meeting: The above conference operations are repeated as
the meeting progresses with any location having the ability to act as
the initiating location or annotate the work of others.
ù Terminate the meeting: End the audiographic conference session.
4.2 Operational phases
The sequence of operations associated with the audiographic conference can
be divided into five phases:
include 710-t01eTime «
Phase Phase Phase Phase Phase
A B C D E
Phase Call set-up
A Conference set-up
Phase Conference session
B Conference recovery and
Phase reconfiguration
C Call release
Phase
D
Phase
E
4.2.1 Call set-up and release (Phases A and E)
The establishment and release of the physical connection between terminal
equipment for point-to-point operation or between terminal and MCU for multipoint
operation, is as defined for a general teleconference call in
Recommendation F.701.
Call release can take place from the MCU (e.g. in the case of the end of
the reservation period), by action of the Convenor or by a participant (his own
connection only).
styleref head_footRecommendation F.710PAG
E9
4.2.2 Conference set-up/recovery (Phases B and D)
As soon as the physical connection between terminals or between terminals
and MCU is established the terminal enters the conference set-up phase. During
the active meeting session the conference set-up phase can be reentered when
participants change.
During the conference set-up phase the participating terminals exchange
information important to the organization of the meeting, such as:
ù terminal identity/authentication;
ù names of participants;
ù terminal characteristics and capabilities.
During conference recovery or reconfiguration, detection of loss of a
connection to a terminal is performed by the terminal assigned responsibility for
controlling the conference. If the controlling terminal is lost then the
conference returns to the non-conducted mode (see S 4.2.3) and conference set-up
procedures are re-initiated.
4.2.3 Conference session (Phase C)
4.2.3.1 The following two modes for conference control are required:
a) Non-conducted Mode: Any participant may speak or initiate graphics or
new image activity at any time.
b) Conducted: A participant makes an active request to speak or initiate
graphics activity. The conference Chairman must actively grant
permission to switch control.
4.2.3.2 Non-conducted session
In the case of the non-conducted mode each participant can speak at any
time he wishes. All microphones can be permanently enabled.
At the start of the conference session, the default mode of conversation
is "non-conducted".
4.2.3.3 Conducted session
In the case of the conducted mode the participant desiring recognition
will issue a request to speak and then wait until the request is granted. The
request to speak can be granted manually or verbally by the Conductor or
automatically by a queueing mechanism within the conference system.
The token of conductorship assigned during the conference set-up phase can
be handed over to another terminal so equipped at any time during the conference
session.
The AGC service shall offer the Conductor and other conference
participants the control functions required to actively conduct and participate
in the conference session. These functions include:
ù request for floor;
ù request granted;
ù request refused.
PAGE10 styleref head_footRecommendation F.710
4.2.3.4 All modes
The Conductor always retains the capability to interrupt the current
speaker, to disable the current speaker's microphone and to pass the "floor" to
another participant.
A means shall be provided at each terminal location for identifying the
speaker and the source of the current image being discussed.
The mode of conference control currently being invoked will be indicated
at each terminal location.
4.3 Capabilities arbitration
A number of network, terminal and MCU-related capabilities are to be
arbitrated during the call control phase. Some of the functions to be arbitrated
are:
ù Interactive functions: Drawing, pointing, editing (raster or document),
undo, and live interaction.
ù Image capabilities: resolution, image type (video, document, etc.) and
pixel depth (bi-level, grey scale or colour).
ù Image compression capabilities: Standardized techniques for specific
image types (such as documents, still frame, video, etc.) and the loss
threshold when non-restoring algorithms are used.
ù Network capabilities: Time outs, add/drop tolerances, audio/data
bandwidth allocation.
ù Conference control: Means of speaker indication and speaker/graphics
control switching.
5 Network aspects
5.1 General
The combination of functions specified for an audiographic terminal
provides a complete audiographic conferencing system which may operate over a
single communications channel, or over multiple communications channels between
two or more locations.
The AGC service must be capable of providing both point-to-point and
multipoint configurations with full interactivity among all units in the
conference. A broadcast mode is also desirable.
The AGC service in the international connections between Administrations
or networks shall use any of the following:
ù on demand connections (automatic switching);
ù reserved or semi-permanent connections (e.g. manual set-up).
It is intended that the AGC service be optimized for operation on one or
more ISDN connections with the audio and graphics data integrated. It is
desirable that the AGC service also be compatible with and available on the
public switched telephone network (PSTN), the circuit switched public data
network (CSPDN) and the packet switched public data network (PSPDN) where the
audio and graphics may be carried in separate circuits.
styleref head_footRecommendation F.710PAG
E9
5.2 Network topology
AGC service can be provided using one of the following configurations as
appropriate to a particular conference requirement:
a) Direct two-party conference
Figure = 0,5 cm
b) Multipoint conference requiring a single MCU
Figure = 2,5 cm
c) Multipoint conference requiring multiple MCUs. A typical example:
Figure = 3,5 cm
5.3 Multipoint operation
The international multipoint AGC service is provided by means of one or
more multipoint control units (MCUs). Each MCU may serve one or more AGC
terminals and be interconnected with other MCUs.
The general functions of the AGC multipoint control unit are as described
in Recommendation F.701. Detailed procedures for multipoint operation are given
in Recommendations H.230/AV.230, AV.231 and AV.440.
There is a need for an automatic service which does not require operator
assistance in setting up conference calls. The possibility of such a service is
addressed in the supplement to the Series-E Recommendations relating to the
operation of the International Telephone service.
6 Terminal aspects
6.1 General
An audiographic terminal is the device by means of which audiographic
conferences are conducted through appropriate communications channels. The term
"terminal", as associated with the AGC service, is meant to imply all equipment
or devices used to input, output and process both the audio and graphics
information signals.
The graphics portion of the audiographic terminal can also serve as a
valuable adjunct to the videoconference and videophone services by providing the
means for the transmission of graphic documentation.
Each terminal used in the AGC service shall have a unique identification.
It is the responsibility of the conference initiating terminal to verify the
identification of the other participating terminals prior to the communications
phase.
6.2 Functional elements
6.2.1 An audiographic terminal provides a number of basic functions as required
by the definition of the AGC service. The audiographic terminal may also provide
a number of auxiliary features which, while not essential to the basic
operational requirement, will greatly enhance the conduct of the audiographic
conference.
6.2.2 The terminal may be composed of the following functional elements (see
Figure 2/F.710):
Figure = 14 cm
6.2.3 The specific details of the AGC terminal are described in Recommendations
AV.310 and AV.311.
6.3 Terminal input requirements
6.3.1 The audiographics terminal is a device for permitting simultaneous
viewing, manipulation and oral discussion of the same image on multiple terminals
linked by one or more telecommunications networks.
6.3.2 The terminal, depending on the application, may have one or more modes of
image input:
ù Scanner: for digitizing images from paper or film.
ù Frame capture: for digitizing still frame video images.
ù Disk media: for importing computer generated images.
ù Interfaces: to other communications equipment for electronically
interchanged images.
ù Creation: of original images and documents within the terminal by means
of resident software (document editor), or by direct drawing
(telewriting).
6.3.3 Both hard copy and soft copy communications can be utilized in the AGC
service. However, the primary conveyor of graphic information in the audiographic
conference is the soft copy communication wherein the same document is displayed
on all terminal displays at the same time. Voice, pointer and/or telewriting may
be used in discussing the displayed document.
6.4 Terminal display
The interactive image display should permit real-time interaction with the
PAGE10 styleref head_footRecommendation F.710
displays at all locations having the same image content at all times.
The terminal display may have a "window" for local viewing (including an
image preview mode) provided that it is obvious to the user that the window is
local only. A multi-window system with the capability to present two or more
sources of graphic information at any given time may be an optional feature of
the AGC service.
It is desirable that any image operation being performed on the network
active image by other terminals shall also be performed on the local terminal in
the same manner even though the local window may be active.
7 Quality of Service
7.1 Voice quality
By the design of the room and/or the equipment, participants should be
allowed to listen and speak simultaneously with a nominal voice quality
equivalent to speech transmission with a bandwidth of 7 kHz.
In those instances when the requirement for graphic information transfer
competes for the bandwidth required to achieve 7 kHz operation, the speech
objective may be relaxed as long as there is no significant difference in speech
quality from that available in the 64 kbit/s ISDN telephony service based on a
bandwidth of 3.1 kHz.
7.2 Graphic quality
A combination of dynamic channel allocation, receive terminal storage
capacity and "transmit ahead" capabilities shall be provided to ensure that
images are available in the image space when required, and competition with the 7
kHz voice objective is reduced to a minimum.
Image manipulations and other processing activities should be accomplished
within the nominal response time associated with the related face-to-face
activity.
To ensure conference call integrity, error protection shall be provided by
the AGC control procedures for the primary mode of operation.
styleref head_footRecommendation F.710PAG
E9
7.3 Maintenance
Terminal to terminal and terminal to MCU quality shall be checked by
various measurements as appropriate for comparable component services.
8 Intercommunications with other services
Provision shall be made for attaching to the following services for audio
operation only:
ù 7 kHz telephony;
ù 3.1 kHz ISDN telephony;
ù 3.1 kHz PSTN telephony;
ù other audiovisual services.
The AGC service may also be used, in whole or in part, to support a
videoconference when required to augment the videoconference service features.
9 Reservation of service
General procedures for the reservation of an international audiographic
conference are as summarized in Recommendation F.701. Specific procedures are
detailed in Recommendation AV.410.
The national and international facilities required for the establishment
of an audiographic conference call shall be open continuously.
PAGE10 styleref head_footRecommendation F.710
