1、- INTERNATIONAL TWCOMMUNICATION UNION / , CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TERMINAL EQUIPMENT AND PROTOCOLS FOR TELEMATIC SERVICES T.90 CHARACTERISTICS AND PROTOCOLS FOR TERMINALS FOR TELEMATIC SERVICES IN ISDN Recommendat ion T.90 Geneva, 1992 STD-ITU-T RECMN T
2、-SO-ENGL 1792 = 48b257L ObL8b47 872 I FOREWORD The CCITT (Lhe International Telegraph and Telephone Consultative Committee) is a permanent organ of he International Telecommunication Union (ITU). CCIT is responsible for studying technical, operating and tariff questions and issuing Recommendations o
3、n them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCIT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCITT between Plenary
4、Assemblies is covered by the procedure laid down in CCIT Resolution No. 2 (Melbourne, 1988). Recommendation T.90 was prepared by Study Group VID and was approved.under the Resolution No. 2 procedure on the 25th of Februaxy 1992. CC NOTES 1) telecommunication Administration and a recognized private o
5、perating agency. 2) In this Recommendation, the expression “Administration” is used for conciseness to indicate both a A list of abbreviations used in this Recommendation can be found in Appendix VU. O ITU 1992 All rights reserved. No part of this pvblication may be reproduced or utilized in any for
6、m or by any means, electronic or mechanical,-.inclyding photocopying and microfilm, without permission in writing from the ITU. STD-ITU-T RECMN TmSO-ENGL 1992 = i-1b2591i Obl8b50 59i-1 Recommendation T.90 CHARACTERISTICS AND PROTOCOLS FOR TERMINALS FOR TELEMATIC SERVICES IN ISDN (revised 1991) Summa
7、ry This Recommendation defines rhe functional profile for base standards ISO/IEC 7776, 8208 and 8885 to provide the lower layers of the telematic Services protocol stack when operating on the ISDN. Parameter values are recommended to ensure good throughput when operating via long delay connections s
8、uch as satellite routes. Backward compatibility with the Bhe Book version has been maintained. Three methods of negotiating the lower layer parameter values have been included to satisfy various connection scenarios, e.g. completely within the ISDN or between the ISDN and other digitai networks. Thi
9、s Recommendation supplies the network layer definition in Recommendation T.70 for telematic terminais but not the transpon layer definition which is stili retained the telematic transpon layer definition. CONTENTS Scope 1.1 General 1.2 Use of bearer capabilities 1.3 Protocol architecture 1SDN 8-chan
10、nel circuit-witched mode (DTE-DTE communication) 2.1 Protocol set 2.2 Application rules ISDN B-channel packet-switched mode (DE-DCE communication) 3.1 Protocol set 3.2 Application rules Support of the OSI-nerwork service 4.1 htionaie for considering the OSI-NS 4.2 CCITT Recommendations and IS0 stand
11、ards 4.3 Requirements for tbe 0.91-NS Addilional X.25 optional user facilities 5.1 Categories of additional functions 5.2 Functions - Recommendation T.90 6 7 8 9 10 Interactions between the D-channel and B-channel Suppi emenras, services Terminal response time Synchronizaiion Higher layer protocols
12、10.1 Group 4 facsimile 10.2 Teletex 10.3 Videotex Annex A - Procedures for connection establishment, connection release and information transfer Annex B - ISDN D-channel packet-switched mode TE-DCE communication) Annex C - Procedures for B-channel negotiation of layer 2 parameters for telematic term
13、inals Annex D - SDL diagram for link set up for SABWSABME procedures Annex E - SDL diagram for link set up to a T.90 compatible terminal for XID procedure Annex F - Terminai selection procedures for ISDN telematic terminal Appendix I - Facsimile terminals in the ISDN Appendix I! - Optional usage of
14、the T.70 NL protocol AppendixIII - Service definitions and state transition diagrams for the data link layer within the B-channel (CS mode) Appendix N - Possible model for telematic endsystems taking into account the D-channeVB-channel coordination function Appendix V - Rate adaptation function Appe
15、ndix VI - Recommended combinations of parameter vaiues to ensure optimum througbput Appendix VII - Alphabetical list of abbreviations. 2 Recommendation T.90 STD-ITU-T RECMN T.70-ENGL 1792 m 48b257L ObLb52 3b7 1 Scope 1.1 General -1 The Integrated services digital network (ISDN) supports a wide range
16、 of voice and non-voice services and applications in the same network via a multipurpose usernetwork interface. This Recommendation describes the requirements for telematic terminals, developed for ISDN application, and connected to an ISDN via an I-Series interface. For example, teletex (defined in
17、 Recommendation T.60), group 4 facsimile (defined in Recommendation T.563) and videotex (defined in Recommendations T. 102 and T.103). Telematic terminals supporting both teletex and group 4 facsimile in mixed mode of operation (defined in Recommendation T.561) are also covered by this Recommendatio
18、n. The terminal selection procedure is defined with particular regard to telematic terminais supporting protocol stacks other than those used by the above-mentioned terminals e.g. group 3 document facsimile transmission on the ISDN according to Annex C.30. Terminal requirements to support other tele
19、matic services are for further sudy. Terminais developed for the provision of telematic services in circuit switched public data networks (CSPDNs), packet switched public data networks (PSPDNs) and public switched telephone networks (PSTNs), using terminal adaptors to access the ISDN are not covered
20、 by this Recommendation (see Note i). Interworking with existing telematic terminals connected to CSPDNs, PSPDNs and PSTNs, thereby maintaining the telematic service integrity, should be possible, but is outside the scope of this Recommendation (see Note 2). This Recommendation includes several nego
21、tiation mechanisms for selection of terminals and optional parameters. NOTES i described in Appendix I. 2 For implementation guideline, consideration of incoming calls and information elements for facsimile terminais are For rate adaptation function, see Appendix V.“ 1.2 Use of bearer capabilities T
22、his Recommendation is based on the use of bearer capabilities defined for the ISDN, using B-channels for the information transfer and virtual circuit connection control and the D-channel for the connection control. The use of both circuit-switched and packet-switched information transfer modes is de
23、fined. The use of tbe frame mode information transfer as defined in Recommendation 1.122, is for further study. 1.3 Prorocoi architecture This Recommendation provides the application rules for other CCITT Recommendations and IS0 standards aiming at end-to-end (DE-DTE) communication through the netwo
24、rk as well as DE-DCE interconnection and support of OSI-network service. The use of existing protocols for ISDN telematic terminals different from those described in 2 and 3 is optional. In the case of Q 2, the use of T.70 CSPDN minmurn header is an additional option. Recommendation T.90 3 2 ISDN B-
25、channel circuit-switch4 mode TE-DTE communication) For this mode the circuit-switched 64 kbit/s unrestricted information transfer capability shail be used. For additional information regarding connection control pbase, see 4 A.l a). For additional information regarding the information transfer pbase
26、, see 6 A. 1 b). 3 2.1 Protocol ser Q.931 ISOGEI 8208 (Note 3) The protocol set applicable to the ISDN B-channel circuit-switched mode (CS mode) is shown in Figure 1R.90. Physical connection OS1 layer control Virtual connection control and infomation transfer ISOKEI i776 DTUTE operation (Note 2) I 0
27、.921 (UPD) I. Dchannel I 1 1.43W1.431 (Note 1) I m5701-91 Nolei-Scc$22.1. Note 2 - Full-duplex single link procedures arc defined as described in $ 223. For service defitiitions and state transition diagrams for the data link layer wihtin the B-channel, see Appendix III. Note 3 - DTE-DTE connection
28、is specified on the basis of ISO/EC 8208 (March 1990) as described in 8 2.2.5. In case of the completion of LLC negotiation, the T.70 NL protocol (CSPDN minimum header, Recommenda- tion T.70. 0 3.3) may optionally be supported in addition to the ISOICEI 8208 and used on a per-call-basis. In case of
29、the failure or the absence of LLC negotiation, ISO/CEI 8208 protocol sha be used. For further information see Appendix II. FIGURE 1m.W 2.2 Application rules 2.2.1 Layer I -Physical layer imerface characteristics The physical interface characteristics shall be in accordance with the I-Series Recommen
30、dations: 1.430 (Basic user-network interface, layer 1 specifications), 1.431 (Primary rate user-network interface, layer 1 specifications). This layer provides full duplex transmission capability. 2.2.2 hyer 2 - D-channel connection control phase Reconimendation Q.921 shaiiapply. _ _ 4. Recommendati
31、on T.90 -. STD*ITU-T RECMN TDSO-ENGL 1972 4Bb257L ObLBb54 L3T Address A B 2.2.3 hyer 2 - B-channel link layer procedure bit 1 2345678 1 1000000 1 0000000 The link layer procedure shall consist of a fulIy symmetrical HDLC procedure as defined in ISOAEC 7776 for DTE-DTE operation compatible with Recom
32、mendation X.75 modified by the application rules defined in Q 2.2.3.2.2. Responses (6) Commands (A) 4 4 2.2.3.1 Address procedure Called terminal 8 The following describes the application of the link addressing procedures of Recommendation X.75. Link addresses (A and B) sha be assigned dynmically on
33、 a per-call-basis according to the following rules: a) the ding terminai shall take address A; b) tbe called terminai shall take address B; C) commands and responses shall be transferred as shown in Figure 2Ir.90; d) A and B addresses are coded as follows (Note): Nute - The terminai will discard aU
34、kames received with an address other than A and B. Calling terminal Commands (6) r-l +I I Responses (A) b M710-90 FIGURE 2n.W _- Recommendation T.90 5 2.2.3.2 Implementation rules In order to achieve full compatibility between different implementations, tbe rules in this section for the implementati
35、on of Recommendation X.75 shall be followed. 2.2.3.2.1 General rules a) The 1988 version (Blue Book) of CCITT Recommendation X.75, 0 2 shall be used as the reference specification. The term “STE“ shall be read as “DTE“. b) c) At present the non-extended mode of operation (Le. modulo 8) and ?he exten
36、ded mode of operation (Le. modulo 128) are defined. For the purpose of this Recommendation, support for modulo 8 is mandatory and modulo 128 is optional. The terminal supporting the extended mode shall also support the non-extended mode. It is strongly recommended that the extended mode of operation
37、 (i.e. modulo 128) be supported. The evolution towards LAPD (modulo 128 oniy) in layer 2 of the B-channel is expected to lead to the use of modulo 128 as the common base modulo in the long term. d) To facilitate interworking between terminal equipments using modulo 8 and modulo 128, negotiation mech
38、anisms specified in this Recommendation shall be used. Layer 2 parameters such as modulo and k parameter may be negotiated out-of-band using the LLC-E. In case of failure or absence of out-of-band negotiation, XID and/or SABWSABME procedures may optionally be used. The XID and SABWSABME procedures a
39、re specfied in Annexes C and D respectively. hex E provides SDL description for negotiation mechanisms between the XID and only the single link procedure (SLP) shall be used. sABM/sABMEprocedures. e) 2.2.3.2.2 Specific application rules The following rules refer to the indicated sections and tables
40、of Recommendation X.75. For the application of the non-extended and extended mode see 8 2.23.2.1 c) and d). 6- Recoinmendation T.90 Table 1C4.75 (non-extended mode) Table 2m.75 (extended mode) 2.3.4.9 Table 7a.25 (non-extended mode) Table 8iX.75 (extended mode) f 2.3.5.3 3 2.3.5.5 8 2.4.3 f 2.4.4.1
41、5 2.4.4.4.1 li 2.4.5.9 4* paragraph 5 2.4.5.9 s* parakaph f 2.4.5.9 last paragraph 5 2.4.7.3 8 2.4.7.3 2nd paragraph li 2.4.7.3 3rd paragraph (seeNote i) 3 2.4.8.1 (see Note 2) 3 2.4.8.2 (see Note 2) 2.4.8.3 2nd paragraph 4 2.4.8.4 5 2.4.8.5 5 2.4.8.6 (see Note 2) I-frames should not be sent with an
42、 empty I field. Non-extended mode N 2 O and N I N 1-32. Extended mode N 2: O and N 5 NI-40. Received empty I-frames shall be treated as valid I-frames. Items ?I), 6) and 7) are not valid (shall not result in the sending of an FRMR). Instead the following actions shall be hplemented. - not expected s
43、upervisory frames with the F-bit set to 1 shall be ignored: - not expected UA or DM response shall be ignod, - frames with an invalid N(S) shall be responded to by sending REI (see 0 2.3.5.2.1 of Recommendation X.751. Frames with a FRMR coni01 field shall not be responded by sending a FRh4R. Bits W,
44、 X, Y and Z set to O indicate that no reason for frame rejection is given. The DTE and the ISDN are not octet aligned and the last paragraph is therefore valid. Higher layers should be notified when timer T3 expires (excessive idle state). Related to the first paragraph, read instead of “next rtspon
45、se” “corresponding response”. In the active channel state, the DTE shall transmit contiguous flans indemudent of the other DTE. The caiiing DTE shaii initiate the link by sending a SM-M (non - vimial connectiOn conml and information transfer is to be achieved using Recommendation Q.921 on SAPI 16. *
46、 mer 3 -Network kzyer procedure Recommendation X.31 (case B) shall apply, so rhat protocols to be applied and application mies are as B.2.3.1 Connection controlphase Recommendation Q.93 1 and the packet layer protocol (PLP) of Recommendation X.25 - information transfer capability -octet 3 (unrestric
47、ted digital information); - transfer mode - octet 4 (packet mode); - user information layer 2 protocol - octet 6 (CCiT Recommendation 4.921); - user information layer 3 protocol -octet 7 (CClT Recomadation X.25, packet layer). b) in aU other cases, mandatory fields shouid be encoded as foliows (the
48、value to be set is given in parentheses following each field description, see Recommendation 4.931): - coding standard - octet 3 (CCrrr standardized codmg); - information transfer capability - octet 3 (unrestricted digital information); - transfer mode - octet 4 (packet mode); - - Fields not require
49、d in the default case but may be explicitly encode user information layer 3 protocol - octet 7 (CCi“ Recommendation X.25, packet layer). c) - smcaire - octet 4a; - coafiguration - octet 4a; - establishment - octet 4% - symmetry - octet 4b. d) Fields to be omiaed: - aii other fields. The low layer compatibility (LLC) information element is not used in PS mode. The use of the LLC in future evolutions of the ISDN packet mode services is for further study. The high layer compatibility (HLC) information element is not used in PS mode. The use of the HLC in fut
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