1、INTERNATIONAL TELECOMMUNICATION UNION Amendment I ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU T.90 i1 I /94 TERMINALS FOR TELEMATIC SERVICES CHARACTERISTICS AND PROTOCOLS FOR TERMINALS FOR TELEMATIC SERVICES IN ISDN Amendment 1 to ITU-T Recommendation T.90 (Previously “CCITT Recommendation
2、“) STD-ITU-T RECMN T-90 AMD 1-ENGL 1994 48b2.571 063b379 887 FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on
3、 them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approv
4、al of Recommendations by the Members of the IT-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). Amendment 1 to IT-T Recommendation T.90 was prepared by the IT-T Study Group 8 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 1
5、 lth of November 1994. The previous version of ITU-T Recommendation T.90 was approved on 25th of February 1992. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1995 All r
6、ights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the IT. CONTENTS Page Summary 1 Modifications . 1 1.1 General 1 Annexe F . Terminal selection proc
7、edures for ISDN telematic terminals F . 1 Introduction . Terminal selection - General F.2 D-channel aspects . F.3 B-channel aspects XID procedures for in-band terminal selection procedure F.3.1.1 General F.3.1.4 TPI coding . Encodings for XID information field negotiation . F.3.2.1 Format identifier
8、 subfield F.3.2.2 Data link subfield F.3.2.5 Application rules for usage of XID (FI = 84) F.3.2.6 Operation of the exchange of XID frames Intenvorking between G3C or G3F terminals and G3 terminals Definition of the usage of supplementary services . F . 1.2 F.3.1 F.3.2 F.4 F.5 2 18 18 Amendment 1 (19
9、94) to Recommendation T.90 (11/94) 1 Amendment 1 (1994) to Recommendation T.90 CHARACTERISTICS AND PROTOCOLS FOR TERMINALS FOR TELEMATIC SERVICES IN ISDN Summary This Recommendation defines the functional profile for base standards ISO/IEC 7776, 8208 and 8885 to provide the lower layers of the telem
10、atic services stack when operating on the ISDN. Attention is also paid to the terminal selection procedure related to telematic services using protocols other than the above e.g. group 3 document facsimile transmission over the ISDN. Parameter values are recommended to ensure good throughput when op
11、erating via long delay connections such as satellite routes. Backward compatibility with the Blue Book version has been maintained. Three methods of negotiating the lower layer parameter values have been included to satis various connection scenarios, e.g. completely within the ISDN or between the I
12、SDN and other digital networks. This Recommendation supplies the network layer definition in Recommendation T.70 for telematic terminals but not the transport layer definition which is still retained as the telematic transport layer definition. Modifications 1) In Table of Contents, add: “Annex F -
13、Terminal selection procedures for ISDN telematic terminal” 2) Modi 1.1 as follows: “1.1 General The Integrated services digital network (ISDN) supports a wide range of voice and non-voice services and applications in the same network via a multipurpose usernetwork interface. This Recommendation desc
14、ribes the requirements for telematic terminals, developed for ISDN application, and connected to an ISDN via an I-Series interface. For example, teletex (defined in Recommendation T.60), group 4 facsimile (defined in Recommendation T.563) and videotex (defined in Recommendations T. 102 and T. 103).
15、Telematic terminals supporting both teletex and group 4 facsimile in mixed mode of operation (defined in Recommendation T.561) are also covered by this Recommendation. The terminal selection procedure is defined with particular regard to telematic terminals supporting protocol stacks other than thos
16、e used by the above-rnentioned terminals e.g. group 3 document facsimile transmission on the ISDN according to Annex CT.30. Terminal requirements to support other telematic services are for further study. Terminals developed for the provision of telematic services in circuit switched public data net
17、works (CSPDNs), packet switched public data networks (PSPDNs) and public switched telephone networks (PSTNs), using terminal adaptors to access the ISDN are not covered by this Recommendation (see Note 1). Interworking with existing telematic terminals connected to CSPDNs, PSPDNs and PSTNs, thereby
18、maintaining the telematic service integrity, should be possible, but is outside the scope of this Recommendation (see Note 2). Amendment 1 (1994) to Recommendation T.90 (11/94) 1 This Recommendation includes several negotiation mechanisms for selection of terminals and optional parameters. NOTES 1 d
19、escribed in Appendix I. 2 For implementation guideline, consideration of incoming calls and information elements for facsimile terminals are For rate adaptation function, see Appendix V.” 3) Add Annex F as follows: Annex F Terminal selection procedures for ISDN telematic terminals (This annex forms
20、an integral part of this Recommendation) F.l Introduction This annex describes the terminal selection procedures for the telematic terminals, for example, the different types of digital facsimile terminals which may be attached to the ISDN. The annex extends the procedures defined in Annexes D and E
21、. It does not replace these annexes but it is more flexible and should be used for future designs. F.l.l full E. 164 number used in a multiple subscriber number supplementary service. There are several mechanisms for terminal selection provided by the ISDN, e.g., sub-addresses or the In addition to
22、the bearer capability, higher layer or lower layer compatibility checking can also be considered as mechanisms for terminal identification. However, these information fields are not universally available particularly on international connections or on calls which do not terminate in the ISDN at both
23、 ends. Therefore an in-band terminal identification mechanism has also been defined to maximize the probability of successful communication. The in-band negotiation takes place by the exchange of XID frames. The format of these fiames is defined in ISO/IEC 8885. A special XID format identifier (FI =
24、 84H) has been allocated to telematic terminal negotiation by the ISO. F.1.2 Terminal selection - General Considering that there is more than one type of 64 kbitk facsimile terminal in the ISDN, the following terminal selection procedure is specified. Figure F. 1 shows the scope of selection for ope
25、ration mode on ISDN. This selection procedure includes backward compatibility to 64 kbit/s facsimile terminals based on the February 1992 version of Recommendation T.90 and the Blue Book 1988, and also provides function selection in multimode terminals. F.1.3 ISDN facsimile calls are established via
26、 the D-channel and the terminal selection fields BC, LLC and HLC shall be used at the calling terminal. At the receiving terminal these fields may not be available. This procedure is referred to as out-band terminal selection. Tables F.l, F.2, F.3 define the parameter values for each type of termina
27、l. F.1.4 Once the ISDN connection has been established it is possible to undertake further negotiation via the B-channel. This negotiation process is based on the exchange of XID frames and is referred to as the in-band procedure. This is an extension of the technique described in Annex C and illust
28、rated in Annex E. A different format identifier FI (FI = 84H) is used in the XID fiame because it is carrying extra information to define telematic terminal types in addition to layer 2 parameters. The previous FI = 82H is defined for general usage, whereas the FI = 84H is defined for ITU-T Recommen
29、dations in the T-series. The contents of the two types of XID frame are shown in Figure F.3 and the SDL diagrams illustrating the start-up procedure are in Figures F.5. In the unusual case that there is some conflict between the in-band and out-band procedures, then, the in-band procedure has preced
30、ence because it takes place later in time. 2 Amendment 1 (1994) to Recommendation T.90 (11/94) . . T.90 1988 and 1992 Version T.90 1994 Versian ISDN facsimile selection I . A T.90 TO81 1170.921631 - Mandatoty Optional FIGURE F.lT.90 The scope of selection procedure for mode of operation on ISDN F.1.
31、5 supported by the ISDN connection, the in-band procedure is required in the B-channel. Where the D-channel information elements defining unambiguously the requested telematic service are not Terminal selection at the called side may have been performed on the Bearer Capability Information Element (
32、BC-IE) only resulting from the only received BC-IE as the out-band compatibility information. The setting of the parameters of the BC-IE, however, is common to the various telematic services. Thus, unless at the calling side prior knowledge about the selection of the compatible terminal at the calle
33、d side is available, this knowledge solely can be gained by applying the in-band negotiation procedure as per 1.4, which takes place after call establishment. However, this may lead to recognizing the non-availability of a compatible terminal, so that the required mode of communication cannot be est
34、ablished in this case. This results in the release of the potentially chargeable call, which, however, only lasted for the short time of the interrogation process. Prior knowledge based on the called number or learned knowledge based on recent attempts to the same E.164 terminal number may be used t
35、o reduce the incidence of these occurrences. F.2 D-channel aspects F.2.1 The BC, LLC and HLC parameters for G3C and G3F facsimile terminals are given in Tables F.l, F.2 and F.3. F.2.1.1 Table F.l shows the BC (Bearer Capability) coding structure for G3C and G3F facsimile transmission. Amendment 1 (1
36、994) to Recommendation T.90 (11194) 3 - - - STD-ITU-T RECNN T.90 AND 1-ENGL 1994 D 4862591 Ub3b384 146 Contents Identifier TABLE F. VT.90 G3C facsimile G3F facsimile Condition Condition Condition Condition for calling for called for calling for called side side side side M M M M BC coding structure
37、for G3C and G3F facsimile transmission I Octet number 2 3 Information elements Length of the bearer capability contents Extension Coding standard Information transfer capability Bearer Capability information element identifier Extension Transfer mode Information transfer rate Extension Layer 1 ident
38、ification User information layer 1 protocol 6 Extension Layer 2 identification User information layer 2 protocol Extension Layer 3 identification User information layer 3 protocol Length I I rm Extension M CCITT standardized M coding Unrestricted digital M information M M M Extension Circuit mode 64
39、 kbitk M M M N N I N M M M N N N 1- N I N M N Sending is mandatory for calling side and checking of its presence and contents is mandatory for called side. Calling side does not send the information elements and called side does not care for the information element. 4 Amendment 1 (1994) to Recommend
40、ation T.90 (11/94) - M O F.2.1.2 transmission. Table F.2 shows the LLC (lower layer compatibility) coding structure for G3C and G3F facsimile TABLE F.2/T.90 LLC coding structure for G3C and G3F facsimile transmission I G3C facsimile G3F facsimile Octet number Information elements Contents Condition
41、for calling side M Condition for called side O side side 1 Low layer compatibility information element identifier Identifier 2 Length M Length of the low layer compatibility contents Extension Coding standard Information transfer capability Extension CCITT standardized coding Unrestricted digital in
42、formation (Note 1) 4 Extension Circuit mode 64 kbit/s M M M O O O Extension Transfer mode Information transfer rate Extension Layer 1 identification User information layer i protocol 5 N N N N N I N N NI Extension Layer 2 identifier operation (Note 2) IS0 7776 DTE-DTE N N N N N N + M Extension Layer
43、 2 identification User information layer 2 protocol Extension Layer 3 identification User information layer 3 protocol Extension Layer 3 identifier operation (Note 2) IS0 8208 DTE-DTE N N N N N N M O N NOTES 1 2 parameter negotiation as described in Annex JQ.93 1. Sending is mandatory for calling si
44、de and checking of its presence and contents is mandatory for called side. If present, called side checks the information elements. Calling side does not send the information elements and called side does not care for the information element. When octet 3a (bit 7) is omitted, out-band LLC negotiatio
45、n is not possible. The LLC IE may be transferred transparently by an ISDN between the called user and the calling user and may be used for Amendment 1 (1994) to Recommendation T.90 (11194) 5 STD-ITU-T RECMN T.90 AMD 1-ENGL 1994 m 48b259L Ob3b386 TL9 F.2.1.3 Table F.3 shows the HLC (high layer compat
46、ibility) coding structure for G3C and G3F facsimile transmission. Octet number Information elements 2 3 Length of the high layer compatibility contents Extension Coding standard Interpretation Presentation method of protocol profile M M M M O O O O TABLE F.3/T.90 HLC coding structure for G3C and G3F
47、 facsimile transmission G3F facsimile G3C facsimile side side (Note 2) Contents Condition for calling side (Note 2) Condition for called side M O 1 Identifier High layer compatibility information element identifier Length M O Extension CCIT standardized coding First high layer characteristics identi
48、fication High layer protocol profile M M M M 4 Extension Facsimile group (Note 1) M M O O Extension High layer characteristics identification Extension Extended high layer characteristics identification 4a N N N N M O N NOTES 2 3 preference. Sending is mandatory for calling side and checking of its
49、presence and contents is mandatory for called side. if present, called side checks the information elements. Calling side does not send the information elements and called side does not care for the information element. In case of G3C mode of operation, facsimile group indicates “Group 2/3”, and in case of G3F, it indicates “Group 4”. Two alternative sets of parameters may be specified according to the HLC selection mechanism in ascending order of 6 Amendment 1 (1994) to Recommendation T.90 (11/94) F.3 B-channel aspects F.3.1 XID procedures for in-band terminal
