1、 International Telecommunication Union ITU-T F.724TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (09/2005) SERIES F: NON-TELEPHONE TELECOMMUNICATION SERVICES Audiovisual services Service description and requirements for videotelephony services over IP networks ITU-T Recommendation F.724 ITU-T F-SER
2、IES RECOMMENDATIONS NON-TELEPHONE TELECOMMUNICATION SERVICES TELEGRAPH SERVICE Operating methods for the international public telegram service F.1F.19 The gentex network F.20F.29 Message switching F.30F.39 The international telemessage service F.40F.58 The international telex service F.59F.89 Statis
3、tics and publications on international telegraph services F.90F.99 Scheduled and leased communication services F.100F.104 Phototelegraph service F.105F.109 MOBILE SERVICE Mobile services and multidestination satellite services F.110F.159 TELEMATIC SERVICES Public facsimile service F.160F.199 Teletex
4、 service F.200F.299 Videotex service F.300F.349 General provisions for telematic services F.350F.399 MESSAGE HANDLING SERVICES F.400F.499DIRECTORY SERVICES F.500F.549 DOCUMENT COMMUNICATION Document communication F.550F.579 Programming communication interfaces F.580F.599 DATA TRANSMISSION SERVICES F
5、.600F.699 AUDIOVISUAL SERVICES F.700F.799 ISDN SERVICES F.800F.849 UNIVERSAL PERSONAL TELECOMMUNICATION F.850F.899 HUMAN FACTORS F.900F.999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. F.724 (09/2005) i ITU-T Recommendation F.724 Service description and requirem
6、ents for videotelephony services over IP networks Summary The purpose of this Recommendation is to define the videotelephony services provided over IP networks. The services enable two users in different locations to have conversational communications over IP networks. The service description, funct
7、ion model, service profiles, application scenarios and requirements of the IP videotelephony services are provided. The IP videotelephony services are one class of the generic services identified in ITU-T Rec. F.720, and their description follows the methodology described in ITU-T Rec. F.701. The re
8、quirements for the IP videotelephony services are derived from the scenarios for different applications the said services can support. Therefore, the services requirements accommodate the demands of different kinds of users and assist in enabling intercommunications between the services provided by
9、different telecom operators and/or different IP videotelephony systems. Source ITU-T Recommendation F.724 was approved on 13 September 2005 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. F.724 (09/2005) FOREWORD The International Telecommunication Uni
10、on (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to s
11、tandardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations i
12、s covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to
13、 indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is ach
14、ieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUA
15、L PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether
16、asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautio
17、ned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. F.724 (09/2005) ii
18、i CONTENTS Page 1 Scope 1 2 References. 1 2.1 Normative References 1 2.2 Informative References 1 3 Definitions 1 4 Conventions 2 5 Prose descriptions . 2 6 Functional model and service profile . 2 6.1 Functional model 2 6.2 Service model . 3 6.3 Service profiles. 4 7 Service scenarios 5 7.1 Busines
19、s videotelephony service scenarios 5 7.2 Residential videotelephony service scenarios 7 8 IP videotelephony service requirements. 7 8.1 User requirements. 7 8.2 Application requirements . 8 8.3 Security requirements. 8 8.4 Authentication and accounting requirements . 8 8.5 Interworking and intercomm
20、unication requirements . 9 8.6 QoS requirements . 10 ITU-T Rec. F.724 (09/2005) 1 ITU-T Recommendation F.724 Service description and requirements for videotelephony services over IP networks 1 Scope This Recommendation provides the service descriptions, function model, service profiles, application
21、scenarios and requirements of the videotelephony services based on the IP network. The objective is to describe the service requirements, facilitate interoperability, and provide a guideline to the user, service provider, network carrier, and administrator as well for deploying videotelephony servic
22、es over IP networks. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references a
23、re subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a do
24、cument within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 2.1 Normative References None. 2.2 Informative References ITU-T Recommendation F.700 (2000), Framework Recommendation for multimedia services. ITU-T Recommendation F.701 (2000), Guideline R
25、ecommendation for identifying multimedia service requirements. ITU-T Recommendation F.703 (2000), Multimedia conversational services. ITU-T Recommendation F.720 (1992), Videotelephony services General. ITU-T Recommendation Y.1541 (2002), Network performance objectives for IP-based services. ITU-T H-
26、series Recommendations Supplement 1 (1999), Sign language and lip-reading real time conversation using low bit-rate video communication. 3 Definitions This Recommendation defines the following terms: 3.1 basic videotelephony service: A videotelephony service supporting basic voice, video, real-time
27、text and optional multimedia data or control facility. 3.2 enhanced videotelephony service: A videotelephony service supporting advanced voice, video, real-time text and at least one type of multimedia data and/or control facility. 2 ITU-T Rec. F.724 (09/2005) 4 Conventions In this Recommendation th
28、e following conventions are used: “shall“ indicates a mandatory requirement. “should“ indicates a suggested but optional course of action. “may“ indicates an optional course of action rather than a recommendation that something take place. 5 Prose descriptions The IP videotelephony service provides
29、real-time end-to-end bidirectional communications between two subscribers in different locations on the IP network by means of voice, video, real-time text and other forms of multimedia data and/or control facility. The way to place a call on IP videotelephony services is the same as that for conven
30、tional telephony services in the sense that the subscriber dials a number, or enters another type of identifier, to initiate a call. In addition to videotelephony calls, the subscriber can also use the videotelephony services in other applications. A subscriber of IP videotelephony services can be l
31、ocated in any place covered by IP networks, e.g., office buildings, meeting rooms, hotels, residences, telephone booths on the street or even on board a transport vehicle. There are two types of IP videotelephony calls: Point-to-point calls; Multiparty calls (utilizing devices for audio, video and t
32、ext mixing, e.g., the Multipoint Control Unit (MCU). There are two major types of IP videotelephony terminals: Videotelephony sets; Softphones running on computers. Other types of videotelephony terminals, such as PSTN videophones, ISDN videophones or even conventional phones and mobile phones, can
33、communicate with the IP videophones. These terminals may have limited capabilities regarding sending or receiving various types of information in videotelephony calls, but they can at least intercommunicate with IP videophones in a voice-only mode. 6 Functional model and service profile 6.1 Function
34、al model The functional model of IP videotelephony services is shown in Figure 1. IP videotelephony terminals exchange voice, video, real-time text and multimedia data in a point-to-point or multipoint way over IP networks. They can also intercommunicate with other videotelephony or conventional tel
35、ephony terminals via interworking units. The call control unit processes call signalling and controls sessions, and the Authentication, Authorization and Accounting (AAA) unit performs the function of user, authentication, authorization and accounting. ITU-T Rec. F.724 (09/2005) 3 Figure 1/F.724 Fun
36、ctional model of IP videotelephony services 6.2 Service model 6.2.1 Service model: the functional view There are two models for IP videotelephony services from the functional view. Other models may exist or can be developed. However, they are a subject beyond the scope of this Recommendation and are
37、 thus for further study. 1) Basic videotelephony services They refer to those IP videotelephony services that support the mandatory basic features. Only the voice, video and real-time text of conversational parties are transmitted between them. 2) Enhanced videotelephony services They refer to those
38、 IP videotelephony services that support the enhanced optional features (i.e., other forms of multimedia data and/or remote control function). In addition to voice, video and real-time text, multimedia data like still pictures, pre-recorded audio/video clips, text messages, and collaboration-related
39、 data such as white-boarding information can be transmitted between videophones. Other optional features should include convening of a conference and control of a conference, support for far-end camera control and other remote control. 6.2.2 Service model: the usage view From the view of use environ
40、ment, there are two types of IP videotelephony services. 1) Residential videotelephony services For residential videotelephony service users, the following applications should be supported: Face-to-face conversation with audio, video, and real-time text; Face-to-face conversation with simultaneous t
41、ransfer of pictographical data such as picture, pre-recorded video clips and files of other kinds; Remote video surveillance for home security inspection and unmanned baby-sitting for kids, etc; Emergency calls in audio, video and text. 2) Business videotelephony services For business service users,
42、 the following applications should be supported: Face-to-face conversation with audio, video, and real-time text; Face-to-face conversation with simultaneous transfer of pictographical data such as images, documents and files of other kinds; 4 ITU-T Rec. F.724 (09/2005) Remote video surveillance; Re
43、mote consultation; Remote diagnosis in telemedicine; Participation in videoconferencing; Emergency calls in audio, video and text. 6.3 Service profiles While all videotelephony services have the common capability for transmission of audio, video and real-time text, they can be divided into different
44、 types of profiles according to the quality level of audio and video, and other multimedia data exchanged. An IP videotelephony service may be offered with two levels of audio quality, three levels of video quality, one level of real-time text, five types of exchanged data and two types of control f
45、acility. The basic audio quality is level A0, equivalent to 3.4 kHz PCM telephony; the enhanced audio quality is level A1, equivalent to 7 kHz or 14 kHz wideband audio. The three levels of video are level V1 for QCIF video, level V2 for CIF video and level V3 for SDTV video. The level of real-time t
46、ext is T2, good conversational text. The five types of exchanged multimedia data are still pictures, video clips, text messages, file transfer and joint editing. The two types of control facility are remote control and conference conductor. Taking into account the factors mentioned above, the follow
47、ing profiles of videotelephony service are defined. The service profile descriptions are not intended to impose a particular and detailed way of offering the services, but to illustrate the approach to the profile definition. Profile a: Basic videotelephony service: basic audio, QCIF or CIF video, r
48、eal-time text, optional multimedia data or control facility; Profile b: Enhanced Basic videotelephony service: wideband audio, CIF video, real-time text, optional multimedia data or control facility; Profile c: Enhanced videotelephony service: wideband audio, CIF or SDTV video, real-time text, multi
49、media data and/or control facility. The above defined service profiles are summarized in Table 1. Table 1/F.724 Service profiles Profile Audio Video Text Still pictures, pre-recorded video clips, text messages, file transfer and/or joint editing Control functions Pa Pb Pc A0 A1 A1 V1 or V2 V2 V2 or V3 T2 T2 T2 O O 1M O O 1M A0, A1 Minimum mandatory audio quality level V1, V2, V3 Minimum mandatory video quality level T2 Mandatory text level 1M At least one of the media components mandatory O Optional
