ITU-T F 761-1993 SERVICE-ORIENTED REQUIREMENTS FOR TELEWRITING APPLICATIONS《电写应用面向业务的要求》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 (b) that telewriting could serve as an optional facility to the general public telephone service, which could be ofinterest to several categories of users (e.g. deaf people, architects, advertising agencies, etc.);(c) that telewriting could support applic

2、ations like educational communication services (“electronicblackboard”);(d) that telewriting could be a facility within a teleconference service;(e) that telewriting could add a graphic-oriented facility to telematic services,concludesthat telewriting can be applied as either a communication service

3、 or a communication technique within otherservices,recommendsthat the service-oriented aspects of telewriting applications be in accordance with this Recommendation.1 General1.1 ScopeThis Recommendation specifies the service-oriented requirements for the application of telewriting incombination with

4、 telephony.Use of telewriting as an independent telecommunication service or in combination with other services thantelephony is for further study.The technical characteristics of telewriting are specified in Recommendation T.150.1.2 DefinitionTelewriting enables the transmission of graphic informat

5、ion to be displayed at the receiving side in accordancewith the writing movements at the sending side. This display is normally effected on a real time basis; a delay in thetransmission may be included.1.3 Applications1.3.1 Telewriting can support:a) explanatory information exchange;b) teleconferenc

6、ing;c) distant teaching or lecturing;d) telecommunication between speech- and/or ear-handicapped people.1.3.2 Applications in combination with services other than the telephone service and/or non-real time applications arefor further study.2 Fascicle II.5 - Rec. F.7612 General characteristics of tel

7、ewriting2.1 The main characteristics of telewriting in this context are real time display and interactive communication duringone session, which requires availability of a terminal at each side. Consequently, both sides of the connection will beable to contribute to the same image.2.2 The presentati

8、on functionalities along with their attributes are described in Recommendation T.150. They allowmainly for: the generation, transfer and representation of curves of arbitrary shapes; the effect of the movement of thewriting instrument at the sending side is retained during reproduction; marking sing

9、le positions in a telewriting image by means of a cursor; erasure of all or part of a telewriting image.2.3 The image input is provided by appropriate writing tools, such as a writing tablet and a writing pencil.2.4 At the originators terminal, the input information is made visible either by a displ

10、ay unit or on the writing tabletitself.2.5 The reproduction at the recipients terminal will take place on a screen, on paper or on any other means, normallyresulting in a real time copy. The writing speed at the transmitting and receiving end should generally be the same.2.6 In principle, any type o

11、f network can be used as a carrier for telewriting signals.3 Telewriting in combination with telephony3.1 The general characteristics are as mentioned in 2.1.3.2 The subset of presentation functionalities available are the default capabilities of the basic terminal as defined inRecommendation T.150.

12、3.3 The following terminal operating modes are defined:a) speech plus telewriting: speech signals and telewriting signals can be sent simultaneously;b) telewriting only: in this mode sending of speech signals is blocked, reception of speech signals is stillpossible.3.4 The public switched telephone

13、network is used for carrying the telewriting information. In practice, a 300 bpssub-channel derived from the available speech channel bandwidth is used.Note Use of the ISDN for carrying telewriting information is for further study.3.5 The quality of service depends on the characteristics of the tele

14、phone network and of the telewriting equipment.In case of simultaneous transmission of speech and telewriting signals, mutual interference should be relativelysmall. Faults caused by speech interference on the telewriting band are not tolerable. The influence of the telewritingsignals on the quality of the speech conversation must be limited.