1、CEPT T/N*31-OL*E 2326434 000b090 3 M T/N 31-01 E Page 1 Recommendation T/N 31-01 E (Nice 1985, revised Edinburgh 1988) INTERNATIONAL DIGITAL VIDEOCONFERENCE SERVICE Recommendation proposed by Working Group T/WG 14 “Network Aspects” (NA) Text of the Recommendation revised adopted by Commission “Telec
2、ommunications”: “The European Conference of Posts and Telecommunications Administrations, considering that there is an increasing demand for videoconference services, and especially for international videoconferencing; such services basic audiovisual facilities and a variety of optional facilities a
3、ccording to customers requirements, and recognising 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
4、members of the CEPT that they should implement an international videoconference service as described and defined in the attachment hereto.” Edition of October 31, 1989 CEPT T/N*3L-OL*E 2326414 000609L 3 TIN 31-01 E Page 3 Contents I . 2 . 3 . 3.1. 3.2. 3.3. 3.4. 3.5. 3.6. 3.7. 3.8. 4 . 4.1. 4.2. 5 .
5、 5.1. 5.2. 5.3. 5.4. 5.5. 6 . 6.1. 6.2. 7 . 7.1. 7.2. 7.3. 7.4. 8 . 8.1. 8.2. 8.3. 8.4. 8.5. 9 . 9.1. 9.2. 9.3. 9.4. SCOPE . 5 DEFINITIONS . 5 SERVICE AND FACILITIES . 7 Service description 7 Basic facilities 7 Optional facilities available . 8 Temporary use of facilities . 9 Terminals 9 Performance
6、s 9 Network access 9 Availability . 9 FUNCTIONAL DESCRIPTION 10 Hierarchical model applied to videoconference . 10 Terminal structure 10 TERMINAL EQUIPMENT AND ACCOMMODATION . 11 11 General disposition of equipment and facilities . Video subsystem . 12 Audio subsystem . 13 Other facilities 13 Custom
7、er information and control 13 TERMINAL ALIGNMENT PROCEDURES 13 Video alignment . 13 Audio alignment . 14 CODING EQUIPMENT . 16 Video codec . 16 Audio codec . 16 Other codecs . 16 Local network transmission . 20 MULTIPLEX STRUCTURE AND TRANSMISSION 20 General description of possible transmission and
8、networking arrangement . 20 Transmission at n x 384 kbit/s on the primary rate access 21 Transmission at other bit rates . 22 Error performance 22 Compatibility with other services 22 MULTIPOINT VIDEOCONFERENCE 22 Network structure . 22 General description of operating modes 22 Additional terminal f
9、acilities 22 Multipoint conference unit . 23 . Edition of October 31. 1989 CEPT T/N*33-O3*E 2326434 OOObO2 5 = T/N 31-01 E Page 4 10. NETWORKARCHITECTURE . . . . . 11. OPERATING PROCEDURES . . . . . 11.1. Reservation . . . . . . . . . . . . . . 11.2. Call set-up and pre-test procedure . . . . . 11 -
10、3. Fault procedure . . . . . . . . . . . . . 12. TARIFFS AND CHARGING ASPECTS . 13. REFERENCES . . . . . . . . . . . . ANNEX 1 : Call reservation arrangements ANNEX 2: Pre-call testing procedure ANNEX 3: Fault procedure ANNEX 4: Service improvements under study . . 23 23 23 23 23 23 23 Edition of Oc
11、tober 31, 19PQ CEPT T/N*3L-OL*E D 2326414 0006093 7 D I. 1.1. 1.2. 1.3. L. 2.1. 2.2. 2.3. 2.4. 2.5. 2.6. O T/N 3-01 E Page 5 SCOPE Introduction An increasing demand for videoconferencing service is now in evidence, resulting from technological progress which makes possible satisfactory performance i
12、n a commercially viable way. Information on human factor aspects is essential, 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
13、Recommendation set out here offers the basic elements for an international 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 th
14、at distinctions between these three services will tend to disappear, 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
15、 between groups of users in two or more separate locations, combining 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 servi
16、ce and facilities offered, technical specifications for equipment, and 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 infor
17、mation which can be used by bodies setting up videoconferencing services. 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 interconne
18、cting transmission media. For a multipoint service, multipoint service 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 co
19、nnection including audio, video, and optional ancillary equipment. It 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 specificatio
20、ns in Sections 5.2., 5.3., 6.1., 6.2. Terminal options Those aspects of 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.,
21、 5.5., 6.3. Video subsystem The part of the terminal which contains video 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 no
22、rmally display the incoming video signal. Edition of October 31, 1989 CEPT T/N*3L-OL*E 2326414 0006094 9 T/N 31-01 E Page 6 2.7. 2.8. 2.9. 2.10. 2.11. 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 came
23、ra That (those) camera(s) which form images of the 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 s
24、ignal according to CCITT Recommendation H.lOO; at 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,
25、 etc. Voice-switched video system The selection 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 int
26、o one or both directions of audio transmission, 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 ter
27、minal together with the primary video and audio paths. This includes for instance facsimile, telewnting 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
28、 in the codec; information injected into the digital 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. Us
29、er-to-user signalhg channel A channel to convey 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 calibratio
30、n of audio and video levels in terminals connected to the videoconference network. Edition of October 31, i989 CEPT T/N*3L-OL*E = 2326434 000b095 O 2.21. 2.22. 2.23. 2.24. 2.25. 2.26. 3. 3.1. 3.2. T/N 31-01 E Page 7 Codec or 2 Mbit/s codec or videoconference codec A unit or a set of equipement inter
31、facing between the terminal and the digital 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 muld
32、ex and the network terminating equipment. In 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 codec is made via a wideband connection. Wid
33、eband connection An analogue connection, 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
34、of the terminal and digital streams 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 terminal and digital
35、streams to and from the transmission muldex. 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 specifications (Section 8.) from digital video, audio and other signals, and splits an inco
36、ming 2,048 kbit/s stream into these same 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
37、from the point of view of customers and 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 audi
38、o facility with moving pictures of participants, 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
39、occasional basis; it is applicable to a variety of types of videoconference terminal, including multi-purpose 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 bid
40、irectional via public telecommunication 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 encryp
41、tion, to ensure confidentiality. In 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, togeth
42、er with transmission capability for additional data and messages. Edition of October 31, 1989 CEPT T/N*3L-OL*E 232b1iL4 000bOb 2 T/N 31-01 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. 3.3.8. Audio system Provided that the videoconference room has adequate acoustic dam
43、ping (e.g., by means of 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 ba
44、ndwidth transmission system, 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; a
45、s a minimum, one screen 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 objec
46、ts, flip chart, documents, 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 choic
47、e, a likely choice being 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
48、ports can be provided operating 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 pe
49、ople, can be combined into 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”) or simult
