CEPT T SF 65 E-1989 Basic Narrow Band Videophone Service in the ISDN《在综合业务数字网(ISDN)中基本窄带可视电话业务》.pdf

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1、CEPT T/SF*b5*E 89 232b434 0009538 L - - T/SF 65 E Page 1 Recommendation T/SF 65 (Vienna 1989 (CAC) BASIC NARROW BAND VIDEOPHONE SERVICE nU THE ISDN” Recommendation proposed by the Working Group T/WG 7 “Services and Facilities” (SF) Text of the Recommendation adopted by the “TelecomrnitnicatioIls” Co

2、mmission : “The European Conference of Postal and Telecommunications Administrations, considering a) that considerable efforts have been undertaken worldwide in order to develop videophone equipment based on rapid improvements in the quality of video codec algorithms, b) that videophones of some com

3、panies are already available on the market, c) that first trials of videophone have been performed nationally as well as internationally, d) that a number of countries intend to introduce the videophone service as soon as possible, e) that the ISDN will be an appropriate network for providing the na

4、rrow band videophone service, f) that ISDN trials are going on in a number of countries, O recogtiizes the need for a standardized international videophone service, which will guarantee the compatibility of videophones on a worldwide basis and it therefore, recommends that the narrow band videophone

5、 service, where implemented, respect the requirements stated in this Recommenda- tion.” 1. DEFINJTION The videophone service is a symmetrical, bi-directional real-time, audiovisual teleservice in which speech and moving pictures are interchanged via the network; the picture information transmitted i

6、s sufficient for adequate representation of fluid movements. Essential feature of the service is that it provides the user, besides videophony, also the possibility to communicate with other telephone or videophone subscribers by using only the speech communication facility. 2. DESCRIPTION O 2.1. Ge

7、neral Description The narrow band videophone service is defined for ISDN networks. Accordingly, videophony is a tele- services Le. a fully standardized service as defined in Recommendations 1.210 and 1.240. The Videophone service employs either one or two basic 64 kbitis channels for audiovisual com

8、munication. The service may support three different modes of operation: 1. Mode I: 1 x 64 kbit/s based on one B-channel where encoded speech and video are allocated in the same channel. 2. Mode II: 2 x 64 kbit/s based on two B-channels where video employs one of the B-channels and audio the other on

9、e. 3. Mode III: 1 x 96 kbit/s or 1 x 112 kbit/s for video and 32 or 16 kbit/s for audio based on two B-channels where video is split between the two B-channels and audio is allocated in one of the channels with video. In case two or eventually three of the modes mentioned above are standardized, int

10、ercommunication must be provided at the audiovisual quality of the lower ranking mode. * This Recommendation is based on CCIT Recommendation F.721. Edition of September 15, 1989 7- -. CEPT T/SF*bS*E 89 = 2326434 0009539 3 T/SF 65 E Page 2 2.2. 2.2.1. 2.2.2. 2.2.3. 2.2.4. 2.2.5. 3. 3.1. The videophon

11、e service is likely to be used in much the same way as the telephone service for personal communication, the enhancement being in the visibility of the communication partners which implies a number of possible new applications. A redundancy and irrelevance reduction technique (codec) in the terminal

12、 allows moving pictures to be displayed continuously in colour, even if transmission takes place at the comparatively low bit rate of the narrow band ISDN. The speech quality of this new service must be at least as good as that applicable to the telephone service in the 64 kbit/s ISDN using a bandwi

13、dth of 3.1 kHz up to 7 kHz (at least no significant difference). The basic videophone service is characterized by the continuous transmission of moving pictures simul- taneoulsy with the speech of the persons involved in the call (generally two in the case of a point-to-point connection) via one or

14、two 64 kbit/s channels. Two different types of calls should be possible: - point-to-point calls (basic requirement), and - multipoint calls (see Note I). Videophone terminals must also be capable of supporting the telephone service. In some installations a videophone will be attached to a passive bu

15、s configuration (S interface) along with terminals for other services (see Note 2). An optional enhancement available in some terminals provides for transmission of images of documents or other objects alternate to face-to-face communication. Transfer of documents at higher resolution may be an opti

16、onal feature. This item requires further study. Necessary Quality Characteristics Synchronism of Speech and Lip Movement (Lip Synchronism) No subjectively discernible difference in the delay of the speech and video signal. Sound Quality No significant difference compared to the speech quality used i

17、n the 64 kbit/s ISDN telephone services based on bandwiths of 3.1 kHz or 7 kHz. Picture Quality Optimization of picture quality is for further study, including the need for adequate representation of fluid movements (see Note 3). The Overall Delay The overall effect on quality by the delays introduc

18、ed by video codecs and transmission facilities needs to be taken into account in the service. If satellite connections are used, then two or more hops are to be avoided, because increased delays may impair user acceptability. The overall delay should in no circumstances under normal conditions excee

19、d x ms (available research indicates that x should not exceed 400 ms). However, further study is required (see Note 4). User Guidance For the convenience of the user, visual user guidance between the videophone system and the user should be preferably provided with the aid of alphanumeric display. P

20、ROCEDURES AND OPERATIONAL REQUIREMENTS Originating the Service (Call Set-up) Two possibilities are required: - Call set-up starting directly as videophone service. - Call set-up by means of a service change, starting from the telephone service. Note 1. For multipoint calls a central facility is requ

21、ired for mixing speech signals and switching and/or combining video signals. This facility is to be defined in an other Recommendation. Note 2. Speech supported only by still picture transmission and/or telewriting is not considered as par of the videophone service. Note 3. The urgent need to develo

22、p both objective and subjective quality parameters for the received motion picture is widely identified. Note 4. Under normal conditions the overall delay is defined to consist of transmission delay and the characteristic delay of a videophone terminal. Characteristic delay of videophone terminal is

23、 the delay introduced by the terminal when only lips and eyes of the talking user are moving. IC- i Edition of September 15, 1989- - - - CEPT T/SF*b5*E 89 D 2326434 0009540 T 3.1.1. 3.1.2. 3.2. 3.3. 3.4. 3.5. 3.5.1. TISF 65 E Page 3 Several service changes between telephony and videophony must be po

24、ssible during a single call (see Note 5). Point-to-point Videophone Call The call set-up procedure form the user?s point of view must be as simple as possible in order to achieve a good acceptability. Call set-up procedure from the user?s point of view: Case 1 : Videophone service from the very begi

25、nning e.g.: - going off-hook - dialling tone - initialization of videocommunication - keying in the number of the.called subscriber-videophone call Case 2: Telephone service first e.g. : - going off-hook - dialling tone - keying in the number of the called subscriber-telephone call - initialization

26、of videocommunication-videophone call Videophone Co flference Call Multipoint videophone call is in other terms the supplementary service ?Videophone conference car?. Conference facilities (three-party service, conference call) within the videophone service should be option- ally provided. Appropria

27、te support (nehvork or user premises equipment) is necessary. The procedures for operation of those conference calls is for further study. As a whole the call set-up procedures require further study due to versatility of the service, multiservice and function terminal environments and wide variety o

28、f alternatives. CaU Release In general, the release of a videophone call should be similar to the release of a telephone call; picture and sound are released simultaneously. Change of Service (see Note 6) - a service change will be controlled via the D-channel; thus several service changes are possi

29、ble during - service change to and from videophony must be possible to other services which need a single B-channel a call, provided an end-to-end 64 kbit/s transparent channel is available, or two B-channels. Addressing of Terminals Additional call set-up functions such as terminal selection on a p

30、assive bus, using multiple subscriber number, may be offered. This is under study. Controls and Indications User Guidance User guidance plays a major role in the acceptance of the videophone service by the subscriber. User guidance may take place in the form of a dialogue between the system and the

31、user. Information concerning the status of the call will be displayed on the screens or on other displays of the calling and the called users. Some standardization of icons is required. The audible call progress signals used in the videophone service should comply to those of the telephone service.

32、User guidance may be based on the display of alphanumeric characters, e.g. on the screen, or by other visual means, and/or on audible announcements. It must be possible for the sending user (cailing as well as called user) to switch on and off the facility ?suppressing the outgoing picture?. In the

33、case that one communication partner does not want to send his own picture to the other, a substitutional image or suitable pictogram should be transmitted and displayed at the remote terminal. Call set-up and user control procedures may need harmonization with those used for voice services. This poi

34、nt is for further study. Note 5. Interrruption of the audio connection recognizable for the users should be avoided when changing between the telephone call and the videophone call. Note 6. Details related to this item are for further study. a-eptember 15, 1989 .,- y CEPT T/SF*bS*E 89 2326434 000954

35、3 L W TJSF 65 E Page 4 3.5.2. 3.5.3. 3.5.4. 4. 5. 5.1. 5.2. 5.3. 6. 7. Additional Items - The display of the called and calling subscribers pictures on the screen should be possible, not necessarily - The subscribers own picture should be switchable on and off, as required. - Hands-free communicatio

36、n and loudspeaking should be optionally possible, simultaneously. Adjustment Using a specific control, e.g. buttonlkey, user may prior call set-up or during the call display the outgoing picture on the screen. The picture may be controlled by such control functions as “zooming”, “focusing”, “brightn

37、ess”, “contrast” and “colour temperature”. Testing of the Outgoing Picture The user can when desired activate a self-test procedure through the codec to test and control the outgoing picture. CHARGING ASPECT It shall be possible to charge for the service on a per-call basis, based on the duration of

38、 the call, the numbers of the called and calling parties, the time of day and mode of operation used (requiring one or two B-channels). Other parameters for use in charging determination may also be available. INTERCOMMUNICATION AND INTERWORKING - Intercommunication with the telephone service and in

39、terworking with PSTN is essential. - Intercommunication with the videoconference service and other audio and visual services is necessary - Intercommunication between videophone services based on different bit rates operation modes is Intercommunication and Interworking with Telephony Considering th

40、e fact that at the beginning of the introduction of the videophone service the number of videophone subscribers compared to the number of telephone subscribers will be negligible, a fundamental requirement must be fulfilled in order to avoid that videophone subscribers could only communicate in a ki

41、nd of a closed user group. It is essential that every videophone subscriber is able to reach from his videophone terminal every telephone subscriber. This condition must be met regardless of the technology (analogue, digital, ISDN) applied in the local exchange to which the other telephone subscribe

42、r is connected. If in case of intercommunication a videophone connection cannot be provided, a telephone call should be immediately initiated. If then no connection results, an appropriate cause indication shall be given. On the other hand, every telephone terminal must be able to reach every videop

43、hone terminal. (The videophone terminal will be a multiservice terminal, e.g. appropriate for videophone calls as well as for telephone calls.) Intercommunication between Different Videophone Services Basic intercommunication between videophone services based on different bit rates will be provided

44、at the audiovisual qualities of the lower bit rate. Intercommunication with Other Audio-visual and Audio-Graphic Services For further study. (but for further study). required. INTERACTION WITH SUPPLEMENTARY SERVICES - Same as for telephony (including conference call). Further study required. - Other supplementary services, e.g. “change of service including change of connection” have to be studied. ATTRIBUTES/VALUES a) Low Layer Attributes b) Access Attributes c) High Layer Attributes d) General Attributes For further study. Edition of September 15, 1989-