CEPT T TR 01-02 E-1985 International Digital Videoconference《国际数字视频会议》.pdf

1、CEPT T/TR*OL-OZ*E 85 = 232bllL4 0010307 9 W: - O Page -O2 E I Recommendation T/TR O1 -02 E (Nice 1985) concerning the international digital videoconference service Recommendation proposed by Working Group T/WG 12 “Transmission” (TR) Text of the Recommendation revised adopted by Commission “Telecommu

2、nications”. “The European Conference of Posts and Telecommunications Administrations, Considering that there is an increasing demand for videoconference services, and especially for international videocon ferencing ; such services basic audiovisual facilities and a vanety of optional facilities acco

3、rding to customers requirements, and Recogn king the need for interconnectability between videoconference rooms in different countries and in different customers premises, preserving not only the correct electrical operation but also satisfactory acoustic and vision conditions. Recommends to the mem

4、bers of the CEPT that they should implement an international videoconference service as described and dened in the attachment hereto.” e - 9 I Edition of November 30, 1985 ! -5 -_ - I - J=r CEPT T/TR*O1-02* 85 U 2326414 0010308 O U T/TR O1 -02 E Page 3 Contents 1. SCOPE 5 2. DEFINITIONS. . 5 3. 3.1.

5、 3.2. 3.3. 3.4. 3.5. 3.6. 3.7. 3.8. SERVICE AND FACILJTIES 7 Service description. . 7 Basic facilities . 7 Optional facilities available 8 Temporary use of facilities 8 Terminals . 9 Performances . 9 Network access . 9 Availability. 9 4. FUNCTIONAL DESCRIPTION . 10 4.1. Hierarchical model applied to

6、 videoconference 10 4.2. Terminal structure. . 10 5. TERMINAL EQUIPMENT AND ACCOMMODATION 11 5.1. General disposition of equipment and facilities 11 5.2. Video subsystem. 12 5.3. Audio subsystem. 13 5.4. Other facilities . 13 5.5. Customer information and control . 13 6. TERMINAL ALIGNMENT PROCEDURE

7、S . 13 6.1. Video alignment. 13 6.2. Audio alignment. 14 7. CODINGEQUIPMENT 16 7.1. Video codec 16 7.2. Audiocodec 16 7.3. Other codecs 16 7.4. Local network transmission 16 8. MULTIPLEX STRUCTURE AND TRANSMISSION . 16 8.1. 16 8.2. Transmission at n x 384 kbit/s on the primary rate access 17 8.3. Tr

8、ansmission at other bit rates 17 8.4. Error performance. . 17 8.5. Compatibility with other services. . 18 General description of possible transmission and networking arrangement 9. =TIPOINT VIDEOCONFERENCE. . 18 9.1. Network structure 18 9.2. General description of operating modes . 18 9.3. Additio

9、nal termina1 facilities . 18 9.4. Multipoint conference unit 18 - _I Edition of November 30, 1985 -=? CEPT T/TR*OL-OZ*E 5 232b414 0010309 2 T/TR O1 -02 E Page 4 10. NETWORK ARCHITECTURE . 19 11. OPERATING PROCEDURES. . 19 11.1. Reservation. 19 11.2. Call set-up and pre-test procedure . 19 11.3. Faul

10、t procedure . 19 12. TARIFFS AND CHARGING ASPECTS . 19 13, REFERENCES. 19 14. DOCUMENT STATUS. 20 ANNEX 1 : Call reservation arrangements ANNEX 2: Pre-call testing procedure ANNEX 3: Fault procedure ANNEX 4: Service improvements under study CEQT T/TR*O1-02*E 5 m 232641LI O010310 9 I 1. 1.1. 1.2. 1.3

11、. 2. 2.1. 2.2. 2.3. 2.4. 2.5. 2.6. T/TR QI -02 E Page 5 SCOPE Introduction An increasing demand for videoconferencing service is now in evidence, resulting from technological progress which makes possible satisfactory performance in a commercially viable way. Information on human factor aspects is e

12、ssential, but can only be obtained in the relevant context during a considerable period of experience. In order to open the new service on the basis of a European standard and to avoid any restraints on the service development the Recommendation set out here offers the basic elements for an internat

13、ional digital videoconference service. Reference is made in this Recommendation to compatibility with other related services, for example audioconferencing and visual telephony: at some time in the future it could be anticipated that distinctions between these three services will tend to disappear,

14、and should then be covered by a single recommendation covering a range of bit rate options. Definition of videoconferencing “The videoconference service is a service for full-duplex bidirectional real-time audiovisual communication between groups of users in two or more separate locations, combining

15、 a good audio facility with moving pictures of those participants, and with optional auxiliary telematic facilities.” Scope of this document This document presents the Recommendation, including definitions, description of the service and facilities offered, technical specifcations for equipment, and

16、 alignment and operating procedures. A number of sections are included as headings only for completeness of the structure of the Recommendation, but in fact require further study. Annex 4 to this document provides supporting information which can be used by bodies setting up videoconferencing servic

17、es. DEFINITIONS Digital videoconference system A complete set of equipment by means of which a videoconference service can be provided, comprising terminal equipment, coding equipment, and digital network equipment with interconnecting transmission media. For a multipoint service, multipoint service

18、 centres are located at network nodes and connected to terminals via several point-to-point connections. Videoconference terminal or terminal The users equipment and accommodation for a videoconference system at each end of the connection including audio, video, and optional ancillary equipment. It

19、must deliver signals to the coding equipment according to the interface specifications in Sections 5. and 6. Minimum terminal That part of the terminal which contains only audio and video equipment and conforms to the specifications in Sections 5.2., 5.3., 6.1., 6.2. Terminal options Those aspects o

20、f a terminal, not falling within the minimum agreed terminal, which a user wishes to have incorporated in the terminal in order to improve the service. The options when present, must conform to the specifications in Sections 5.4., 5.5., 6.3. Video subsystem The part of the terminal which contains vi

21、deo equipment including cameras, monitors, control and switching of video, video mixers, etc. In the following, the term monitor applies to both CRT monitors and video projectors. Principal monitor That (those) monitor(s) which normally display the incoming video signal. I I_ Edition of November 30,

22、 1985 -7 I CEPT T/TR*OL-OZ*E 85 H 2326414 0010311 O T/TR O1 -02 E Page 6 2.7. 2.8. 2.9. 2.10. 2,Il. 2.12, 2.13, 2.14. 2.15. 2.16. 2.17. _- 2.18. 2.19. 2.20. Local view monitor A monitor which normally displays the outgoing video signal. Conference camera That (those) camera(s) which form images of t

23、he participants at a videoconference. Document camera A fixed camera disposed to view documents or objects placed on a horizontal surface. Auxiliary camera Any other camera. Split-screen transmission Two video sources are combined into a single video signal according to CCITT Recommendation H.lOO; a

24、t the receiving terminal the images may be split and displayed on adjacent monitors. Audio subsystem The part of the terminal which contains the audio equipment including microphones, loudspeakers, amplifiers, audio mixers, echo suppressors/cancellers, etc. Voice-switched video system The selection

25、between video signals from two or more conference cameras is determined by the level from corresponding microphones. Voice controlled audio system To prevent echo between remote locations either a voice switch (echo suppressor) switches attenuation into one or both directions of audio transmission,

26、or an echo canceller is employed to cancel the coupling between loudspeaker and microphone. Ancillary subsystem Any equipment or facility for communication between participants in a videoconference, the signals for which are conveyed to or from the terminal together with the primary video and audio

27、paths. This includes for instance facsimile, telewriting or electronic blackboard, still picture television (SPTV), etc. Codec information and control Digital information issued from the terminal to effect control of the video and/or transmission coding in the codec; information injected into the di

28、gital stream to ensure complementary operation of coders and decoders. User-to-network signalling channel A channel separate from the user information to convey the necessary signalling for dialogue with the network, as for call Set-up or clear down. User-to-user signalling channel A channel to conv

29、ey user-to-user information for service management. Maintenance and monitoring signals Necessary signals on a local or remote basis which provide monitoring of the terminal equipment. Alignment procedures A set of measurements which specify the calibration of audio and video levels in terminals conn

30、ected to the videoconference network. - Edition of November 30, 1985 CEPT T/TR*OL-OZ*E 5 W 2326434 00303L2 2 2.21. 2.22. 2.23. 2.24. 2.25. 2.26. 3. 3.1. 3.2. T/TR O1 -02 E Page 7 Codec or 2 Mbit/s codec or videoconference codec A unit OS a set of equipement interfacing between the terminal and the d

31、igital network. In particular it provides analogue to digital conversion, compression and coding of information and the reverse operation. It may comprise the video codec, the audio codec, the interfaces to digital equipment in the terminal, the transmission muldex and the network terminating equipm

32、ent. rn some network configurations, the video- conference codec may be located in a network node or in the international gateway and shared by several terminals: in such cases the connection between a terminal and the codecis made via a wideband connection. 5 Wideband connection An analogue connect

33、ion, or a digital connection using a high bit rate codec, which carries the signals between a terminal and the videoconference codec through a wideband network. Video codec A part of the videoconference codec having interfaces with both the analogue video signals of the terminal and digital streams

34、to and from the transmission muldex. It carries out redundancy reduction, compression and coding of video information. Audio codec A part of the videoconference codec or a separate unit having interfaces with the analogue audio signals of the tesminal and digital streams to and from the transmission

35、 miildex. Transmission muldex A part of the videoconference codec or a separate unit which composes an outgoing 2,048 kbit/s digital stream; according to the interconnection specications (Section 8 .) from digital video, audio and other signals, and splits an incoming 2,048 kbt/s stream into these s

36、ame components. Network interface unit A part of the videoconference codec, or a separate unit, which ensures the electrical interface between the transmission muldex and the network access. SERVICE AND FACILITIES This section defines the videoconference service from the point of view of customers a

37、nd marketing organisation. Further details, including technical specifications, are considered in later sections of the Recommendation. Service description A service for real time communication between groups of users in different locations, combining a good audio facility with moving pictures of pa

38、rticipants, and optional auxiliary facilities such as still pictures, facsimile, telewriting, character or graphic format, etc. The service is applicable to companies private videoconference rooms, as well as to public-access videoconference rooms for hire on an occasional basis; it is applicable to

39、 a vaiiety of types of videoconference terminal, including multi-puspose committee rooms used only part-time for videoconferencing as well as dedicated studios; it is applicable also to “mobile” or “site-transferable” videoconference facilities. The service is bidirectional via public telecommunicat

40、ion networks, and provides for interconnection of 2 or more terminals on an equal basis (the possibility of adding more terminals to a call, perhaps on an audio-only basis, is under study). Users may require the implementation of certain measures, including encryption, to ensure confidentiality. In

41、the case of switched calls, the user must be assured of availability, for example by advance reservation, and may also require an assurance of confidentiality. Basic facilities The basic facilities consist in the primary means for audiovisual communication, together with transmission capability for

42、additional data and messages. .- - Edition of November 30, 1985 CEPT T/TR*O1-02*E 5 E 2326414 0010313 4 I T/TR 01-02 E Page 8 3.2.1. 3,2.2. 3.3. 3.3.1. 3.3.2. 3.3.3. 3.3.4. .3.3.5. 3.3.6. 3.3.7. 3.4. Audio system Provided that the videoconference room has adequate acoustic damping (e.g., by means of

43、 drapes and carpet) participants may listen and speak simultaneously; speech transmission is of 0.3-3.4 kHz bandwidth, though the perceived audio quality is considerably better than telephony because better transducers are used. In anticipation of standardisation of a wider bandwidth transmission sy

44、stem, the terminal audio equipment is specified to have a minimum bandwidth of 8 kHz (section 5.3.). Microphones are fixed in position; loudspeakers are associated with the picture screens. Vision system There are a variety of “basic” configurations, according to user needs; as a minimum, one screen

45、 is provided for the display of incoming video signals (in colour), and one colour camera mounted closely above this screen televises a view of all or some of the participants; further cameras may be provided for a variety of purposes (e.g., more participants, display of objects, flip chart, documen

46、ts, etc.+in this case local control is provided for the selection of a single outgoing video signal. In general, participants will sit at a preferred distance of six times the picture height from the picture screen; the choice of picture size will be a matter of customer choice, a likely choice bein

47、g approximately 600 mm diagonal (360 mm picture height, 2 metre viewing distance). Optional facilities available Here follows a list of the auxiliary facility options which are available in the videoconference system of this Recommendation. Data transmission Standardised data ports can be provided o

48、perating at 64 kbit/s. These enable data transmission to be carried out during the call. Data transmission service at 32 kbit/s is possible via the codec interface (see Section 8.2.) by bilateral agreement. Split-screen The outputs from two cameras, each viewing up to three people, can be combined i

49、nto a single video signal; similarly, at the remote end, the two half-height pictures can be separated for display on two adjacent screens. Still picture TV system Whereas for pictures of participants it is necessary to preserve the motions accurately, for other objects (charts/diagrams, documents, solid objects) it is often more important to preserve the clarity of the image: the system provides for the transmission of such images, either very rapidly by temporary displacement of the participant-picture transmission (this is known as “graphics mode