1、CCITT RECMN*F*720 92 m 48b259L 0575728 8T7 m INTERNATIONAL TELECOMMUNICATION UN ION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEMATIC, DATA TRANSMISSION, ISDN BROADBAND, UPT AND TELECONFERENCE SERVICES: OPERATIONS AND QUALITY OF SERVICE F.720 (08/92) VIDEOTELEPHONY SER
2、VICES - GENERAL Recommendation F.720 rl CCITT RECMN*F*720 92 m 48b259L 0575729 733 m I $.I I 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, ope
3、rating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCIT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of
4、 Recommendations by the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (MeIbounie, 1988). Recommendation F.720 was prepared by Study Group I and was approved under the Resolution No. 2 procedure on the 4th of August 1992. CCITT NOTE In thi
5、s Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication Administration and a recognized private operating agency. O ITU 1993 Ail rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic o
6、r mechanical, including photocopying and microfilm, without permission in writing from the ITU. CCITT RECflN*F*720 92 = VBb259L 0575730 V55 Recommendation F.724 VIDEOTELEPHONY SERVICES - GENERAL (1992) The CCllT, considering (a) that videotelephony services bave been introduced in pilot form in vari
7、ous network environments in a number of countries; (b) that videotelephony services are liable to be demanded by users around the whole world; (c) that users will expect an acceptable minimum Quality of Service; (d) that users wiil expect an ease of use comparable to ordinary telephony; (e) that use
8、rs will expect a high level of interoperability with other audiovisual services and with telephony, adopts the subsequent Recommendation dealhg with the general description for videotelephony services. The relevant attributes and values are incorporated as part of each dedicated service description.
9、 CONTENTS 1 Introduction Definition Description Procedures Network aspects Terminal aspects Qudity of Service Interworking and intercommunication requirements Introduction The purpose of this Recommendation is to defme and describe the general features and attributes of the videotelephony service re
10、gardless of the network environment where the service might be provided. The videoteleqbony service is classified in the following two main categories: - - videotelephony service for narrow-band networks; videotelephony service for broadband networks. Recommendation F.720 (08/92) 1 CCITT RECMN*F-720
11、 92 4862593 0575733 371 M I I Videotelephony seMces The intention is to assign a ddicated Recommendation for each type of videotelephony service in specific networks. The dedicated Recommendation is due to contain a description in detail of the service concerned with all relevant characteristics and
12、 attributes. Recommendation E721 covers the basic videotelephony service in the Integrated services digitai network (ISDN) due to this classification. Dedicated service Recommendations for higher quality videotelephony services are for further study. The higher quality videotelephony service will no
13、t necessarily employ any fixed information transfer rate as variable bit rate coding may be used. The classification of videotelephony services is depicted in Figure 1F.720. I I Videotelephony for Videotelephony for narrowband networks broadband networks I FIGURE l/F.72 Classlflcaiion of videoteleph
14、ony services I 2 Definition _- Videotelephony service is an audiovisual conversational teleservice providing bidirectional symmetric real- time transfer of voice and moving colour picaires between two locations (person-to-person) via the networks involved. The minimum requirement is that under norma
15、l conditions the picture information transmitted is sufficient for the adequate representation of fluid movements of a person displayed in head and shoulders view (see Note). - d - 4 - Note - The smoothness of the movements in the reproduced picture is essentially dependent on the amount of motion w
16、ith respect to the transfer rate of transmitted picture information. The above requirements are supposed to be met under such conditions where the amount of motion is limited or the throughput is high enough not to impair the received picture. Degradation is likely to appear as increased blurring an
17、d jerkiness in the reproduced picture. Besides this, other artifacts may occur. 1 Videotelephony teleservice for I I I ISDN (Recommendation F.721) I-. Note 2 I 3 Description Broadband videotelephony services (Recommendation F.722) 3.1 General description The plain videotelephony service includes onl
18、y the basic user requirements, namely speech and motion picture with essentiai controls and indications; the service can be enhanced with options providing auxiliary facilities such as transmission of high resolution still images of documents, photographs, drawings, charts, objects, etc. (see Note).
19、 Note - Speech supported only by still picture transmission and/or telewriting is not considered as a part of the videotelephony service. This type of communication may either be considered as a separate audiovisual service or as a form of audiographic conference service in a point-to-point configur
20、ation. 2 Recommendation F.720 (OW2) CCITT RECMN*F.720 92 rl8b259L 0575732 228 The videotelephony service is likely to be used in much the same way as the ordinary telephone service for individual communication, the enhancement being in the visibility of the communicating parties which implies a numb
21、er of possible new applications. An essential feature of the service is that it is always provided in conjunction with ordinary telephony allowing the user to intercommunicate with all kinds of audiovisual services by using merely the speech communication facility of a videotelephone terminal. in ot
22、her words, videotelephone terminais must be capable of supporting telephony. A videotelephony service may also be used in applications such as communication of speech - and hearing - impaired persons using sign language and remote surveillance where the speech communication facility is of minor impo
23、rtance. In case the service is provided in a network and terminal environment which offers a number of different quality levels depending, among others, on the transmission medium used and respective charging, it must be possible for the user to select the levevmode of operation and/or type of video
24、telephony service he/she wishes and also change it during the caii if provided by the network or supported by the terminals. The latter option may be provided as a supplementary service. Two different types of call shall be possible: - point-to-point calls: - multipoint calls (see Note). Note - For
25、multipoint cas a unit for mixing speech signals and/or combining video signals is required. This will be defined in another context later. 3.2 Description of various videotelephony services Two primary videotelephony service categories have been identified, for narrow-band networks and for broadband
26、 networks. The principle features of either type of service are described below. 3.2.1 Videotelephony service for narrow-band networks The videotelephony service for narrow-band networks provides end-to-end communication of moving colour picares with spatial resolution, temporai resolution and quali
27、ty equivalent to that obtainable by coding the video signal according to Recommendation H.261 (QCIF and CIF format). The videotelephone service may be optionally enhanced by facilities such as the transfer of still pictures, graphics, text and end-to-end control messages. A basic videotelephone tele
28、service for the narrow-band ISDN has been fully standardized according to Recommendations 1.210 and 1.240. The stage 1 description for the videotelephony teleservice for ISDN is contained in Recommendation F.721. In the future, basic videotelephony services for other narrow-band networks (e.g. radio
29、 mobile networks, private networks) could be envisaged. 3.2.2 Videotelephony service for broadband networks The videotelephony service for broadband networks provides end-to-end communication of moving colour pictures with high spatial and temporal resolution and video quality equivalent to conventi
30、onal TV standards (PAL, SECAM, NTSC) or better and enhanced voice/sound quality, possibly stereo transmission and optionally facilities for the transfer of sti pictures, graphics, text and end-to-end control messages. 3.3 Applications related to videotelephony The videotelephony service can be utili
31、zed in a broad range of applications depending on the Quality of Service for audio andor video that can be achieved in different types of services. Recommendation F.720 (OW2) 3 CCITT RECMNJF.720 92 M 486259L 0575733 Lb4 A videotelephony service employing the bearer capabilities of broadband networks
32、 is expected to meet the needs of the subsequently listed applications. Because of the high video quality, this service provides, besides the means for face-to-face dialogue, the possibility to transfer any kind of moving scenes. Also pictures of three- dimensional objects, graphic materiai, e.g., s
33、ketches, drawings, photographs and documents containing text and graphihs can be transferred without any restrictions. Commercial and domestic scenes, instruction procedures and films can be transferred to the communication partner. The constraints imposed by limited transfer capability of narrow-ba
34、nd networks on spatial and temporal image resolutions make certain types of communication less applicable to the videotelephony service for narrow-band networks. Taking into account the aspects mentioned above, the foilowing principle applications of videotelephony are possible among others: a) b) c
35、) d) remote video surveillance; e) face-to-face dialogues involving at least head-and-shoulder images; dialogue including interactive viewing of documents such as sketches, diagrams or charts and objects that can be shown on the screen; access of the user to videoconferences; communication between h
36、earing and speech impaired persons using the sign language. Based on these examples, other enhanced videotelephone applications may also emerge. The user should be given the possibility to select the essential parameters best suiting his specific application. For instance, in applications b) high sp
37、atial resolution is required and on the other hand in e), good motion tolerance is important. Moreover, the transfer rate used for audio should be selectable, in particular when it has charging or video quality implications. 3.4 Supplementary services and enhancements The same spectrum of supplement
38、ary services supporting telephony is in principle applicable for videotelephon y. Other supplementary services or enhancements, dedicated to videotelephony, e.g. videotelephony conference services, are for further study. Relevant enhancements are those supporting the transfer of high resolution stil
39、l pictures and graphics information in a variety of formats like digitized video or other standard document formats. A papedfim scanner or video frame capture may be used as an image input source. Besides this, the possibility to access electronic mail or videotex services with a videotelephone term
40、inal may be supported. 3.5 Specific terminology Fall back Procedures performed either by the network or by the calling terminal that aiiows the calling user to be connected in any case with the called user at any terminal where the call is offered (3.1 kHz telephone terminal or videotelephone termin
41、al). 4 Procedures 4.1 General The call control procedures should be from the users point of view as simple as for ordinary telephony in order to achieve good acceptance. The audible signalling tones must have the same meaning as for telephony. Visual guidance with the aid of the videotelephone termi
42、nal display may play an important role in the invocation and operation of the service. 4.2 Provisiodw thdrawal Provision of the service will be by airrangement with the relevant Administration. . 4 Recommendation F.720 (08/92) 4.3 Normu1 procedures 4.3.1 Activatioddeactivatiodregistration Not applic
43、able. 4.3.2 Invocation and operation 4.3.2.1 Call request The call Set-up must be available for the user as a single operation, preferably not different from that for telephony. As a user option, the terminal can instead be set such that video communication is established only when requested by the
44、users. If a call attempt involves more than one transmission channel, and not all transmission channels are available for the call (for whatever reasons), the call shall stiil proceed with the best level of video quality available. It must be possible for the user to select the transmission rate or
45、other relevant parameters affecting on the service quality and respective service and tariff class. Call Set-up from the users point of view can be optionally executed by initiating fust the voice communication and adding the videocommunication after the connection has been established. 4.3.2.2 Call
46、 release In general, the procedure for disconnecting a videotelephone call shall be the same as for ordinary telephony. Speech and e shall be disconnected simultaneously. 4.3.2.3 Change of service During a single call the change of service can be executed unrestricted as desired by the users with th
47、e aid of in-call modification procedures if provided by the network. A change of selected audiovisual capabilities is provided by in-band signalling and protocols. 4.3.2.4 Videotelephony conference call Conference facilities supporting the videotelephony service are necessary either in the network a
48、ndior at the The procedures and functions are for further study. user premises. 4.3.2.5 Controls and indications 4.3.3 User guidance User guidance can take place in the form of dialogue between the system and the user: information concerning the status of the call can be displayed on the screen or o
49、n another possible display of a videotelephone terminal (both the calling and called party can apply). Guidance may be based on the display of alphanumeric characters in a selectable language, or by other visual means accompanied by appropriate audible announcements taking into account the needs of hearing and speech impaired users. The audible call progress signals used in any videotelephony service shall comply with those of ordinary telephony. Visual counterparts of the audible call progress signals should be defined and standardized. It must be possible for
