1、STD.IS0 7776-ENGL 3995 m 4853903 Ob96807 UT7 INTERNATIONAL STANDARD ISO/IEC 7776 Second edition AMENDMENT 1 1995-07-01 1 996-1 1-1 5 Information technology - Telecommunications and information exchange between systems - High-level data link control procedures - Description of the X.25 LAPB-compatibl
2、e DTE data link procedures AMENDMENT 1 : Modulo 32 768 and m u It -se lect ive reject opt i on Technologies de linformation - Tlcommunications et change dinformation entre systmes - Procdures de commande de liaison de donnes haut niveau - Description des procdures de liaison dquipement terminal de t
3、ransmission de donnes ETTD compatible X. 25 LAP6 AMENDEMENT I: Option de rejet modulo 3.2 768 et multislective This material is reproduced from IS0 documents under International Organization for Standardization (ISO) Copyright License number IHSIICCll996. Not for resale. No part of these IS0 documen
4、ts may be reproduced in any form, electronic retrieval system or otherwise, except as allowed in the copyright law of the country of use, or with the prior written consent of IS0 (Case postale 56,1211 Geneva 20, Switzerland, Fax +41 22 734 10 79), IHS or the IS0 Licensors members. Reference number I
5、SO/IEC 7776:1995/Amd.l:1996(E) STD-IS0 777b-ENGL 1775 = Y853703 Clh7b808 T33 ISO/IEC 77761995/Amd.l:1996(E) Foreword IS0 (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the specialized system for worldwide standardization. National bo
6、dies that are members of IS0 or IEC participate in the development of Internationat Standards through technical committees established by the respective organization to deal with particular fields of technical activity. IS0 and IEC technical committees collaborate in fields of mutual interest. Other
7、 international organizations, governmental and nongovernmental, in liaison with IS0 and IEC, also take part in the work. In the field of information technology, IS0 and IEC have established a joint technical committee, ISO/I EC JTC 1. Draft International Standards adopted by the joint technical comm
8、ittee are circulated to national bodies for voting. Publication as an International Standard requires approval by at least 75 % of the national bodies casting a vote. Amendment 1 to International Standard ISO/IEC 7776:1995 was prepared by Joint Technical Committee ISO/IEC JTC 1, information technolo
9、gy, Subcommittee SC 6, Telecommunications and information exchange between systems. O ISO/IEC 1996 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, w
10、ithout permission in writing from the publisher. Printed in Switzerland ISO/IEC Copyright Office Case postale 56 CH-121 1 Genve 20 Switzerland ii O ISOIIEC STDDISO 777b-ENGL 1775 4851903 Ob7b807 97T W ISOAEC 7776:lggUAmd.l: 199(E) Introduction This amendment to ISOIIEC 7776:1995 adds the multi-selec
11、tive reject option (option 3.3) and modulo 32 768 (option 10.2) from ISO/IEC 7809:1993. This amendment enhances ISO/IEC 7776:1995 in the following areas: it allows more efficient recovery of errored or lost I frames by selectively requesting retransmissions of one or more I frames with a single requ
12、est; this improved efficiency is especially beneficial over links that have high data rates or large propagation delays. link efficiency is improved by retransmitting only errored or lost I frames; correctly received I frames are saved by the DTE for deferred delivery; allows for a much larger modul
13、o for operation over links that have high data rates or large propagation delays; the maximum number of outstanding frames k can be as large as the modulus number minus 1 ; the additional procedures are fairly simple to implement. iii STD-IS0 777b-ENGL 1995 4851701 Ob9bBLO b91 ISO/IEC ISOAEC 7776:19
14、95/Amd.l: 1996(E) Information technology - Telecommunications and information exchange between systems - High-level data link control procedures - Description of the X.25 LAPB-compatible DTE data link procedures AMENDMENT 1: Modulo 32 768 and multi-selective reject option Page 1 Clause 1 Replace par
15、agraph 2 with the following: Clause 3 describes three frame structures: one for basic (modulo 8) operation, one for extended (modulo 128) operation, and the third for modulo 32 768. Basic (modulo 8) operation is the ISOIIEC balanced asynchronous class of procedure with optional functions 2 and 8 (BA
16、C, 2, 8). Extended (modulo 128) operation is the ISOAEC balanced asynchronous class of procedure with optional functions 2, 8, and 10.1 (BAC, 2, 8, 10.1) or 3.3, 8 and 10.1 (BAC, 3.3, 8, 10.1). Modulo 32 768 operation is the ISO/IEC balanced asynchronous class of procedure with optional functions 3.
17、3, 8 and 10.2 (BAC, 3.3, 8, 10.2). The following pertains to the selection of the above combinations: a. basic (modulo 8) operation may optionally be supported - if supported, then the REJ recovery mechanism shall be supported with this operating mode: support of SREJ-with-span-list recovery mechani
18、sm is prohibited; b. extended (modulo 128) operation may optionally be supported - if supported, then either or both of the REJ and SREJ-with-span-list recovery mechanism shall be supported but only one recovery mechanism shall be used at a time; c. modulo 32 768 operation may optionally be supporte
19、d - if supported, then SREJ-with-span-list recovery mechanism shall be supported with this operating mode; support of the REJ recovery mechanism is prohibited. For those DTEIDCE connections that support basic (modulo 8) operation, extended (modulo 128) operation and/or modulo 32 768 operation, the c
20、hoice of modulo and, when applicable, recovery mechanism is made at subscription-time only. For those DTEremote DTE connections that support basic (modulo 8) operation, extended (modulo 128) operation and/or modulo 32 768 operation, the choice of modulo and, when applicable, recovery mechanism is ma
21、de by bilateral agreement. NOTE - The procedure herein descnbed as basic (modulo 8) operation is the only one available in all public data networks Page 1 Clause 1 Replace paragraph 4 with the following: 1 STD.IS0 777b-ENGL 1995 9851903 Ob7b811 528 W F ISOAEC 7776:1995/Amd.l: 1996(E) A C I FCS I F 0
22、 ISOAEC o1 11 11 10 Clause 4 describes the elements of procedures. Some aspects are only operable for the basic (modulo 8) operation, some for the extended (modulo 128) operation and some for modulo 32 768 operation. 8-bits *-bits 16-bits O1 1 1 1 1 1 O Page 2 Flag Address Control Information FCS F
23、A C I FCS 01111110 8-bit *-bits N-bits 16-bits Clause 3 Flag F 01111110 Replace paragraph 1 with the following: All transmissions on a SLP are in frames conforming to one of the formats of table 1 for basic (modulo 8) operation, or one of the formats of table 2 for extended (modulo 128) operation or
24、 alternatively one of the formats of table 3 for modulo 32 768 operation. The flag preceding the address field is defined as the opening flag. The flag following the FCS field is defined as the closing flag. Page 3 Clause 3 Add the following new Table 3, and renumber all the other tables that follow
25、: Table 3 - Frame formats - modulo 32 768 operation Bit order of transmission Bit order of 12345678 12345678 1 to 16 to 1 12345678 Flag I Address 1 Control I FCS I Flag transmission 12345678 12345678 1 to * 16 to 1 12345678 FCS = Frame Check Sequence * 32 for frame formats that contain sequence numb
26、ers; 8 for frame formats that do not contain sequence nun Page 3 Subclause 3.3 Paragraph 1, Replace with the following: For basic (modulo 8) operation, the control field shall consist of one octet. For extended (modulo 128) operation, the control field shall consist of two octets for frame formats t
27、hat contain sequence numbers, and one octet for frame formats that do not contain sequence numbers. For modulo 32 768 operation, the control field shall consist of four octets for frame formats that contain sequence numbers, and one octet for frame formats that do not contain sequence numbers. The c
28、ontent of this field is described in 4.1. 2 0 ISOAEC STDmISO 777b-ENGL 1795 4851703 Ob7b8L2 4b4 ISOAEC 7776:1995/Amd.l: 1996(E) Page 3 Subclause 3.4, Paragraph 1, Line 2: Change 4.3.9 to 4.3.70 Page 3 Subclause 3.4, Paragraph 3: Change 4.3.9 to 4.3.10 and 5.7.3 to 5.8.3. Page 5 Subclause 3.7.1 Repla
29、ce paragraph 3 with the following: The FCS shall be transmitted to the line commencing with the coefficient of the highest term, which is found in bit position 16 of the FCS field (see tables 1, 2 and 3). Page 5 Subclause 3.7.1, NOTE Change “8“ to “75“. Page 7 Subclause 3.1 1.2.2 Change 5.7.1.5 to 5
30、.8.1.5. Page 7 Subclause 3.1 1.2.2, Note Change 5.7.1.3 to 5.8.1.3. Page 7 Subclause 4.1.1 Replace the second paragraph with the following: Three types of control field formats are used to perform numbered information transfer (I format), number supervisory functions (S format) and unnumbered contro
31、l functions (U format). The control field formats for basic (modulo 8) operation are depicted in table 4, control field formats for extended (modulo 128) operation are depicted in table 5 and control field formats for modulo 32 768 operation are depicted in table 6. 3 STD-IS0 777b-ENGL 3775 m 485370
32、3 Ob7b8L3 3TO m 12 8 16 o. 1 ossxxxxx . x N(S) ISOiEC 7776:1995/Amd.l: 1996(E) 17 18 32 P/F N(R) P/F N(R) Page 8 Renumber Tables 3 and 4 as Tables 4 and 5 and insert the following new Table 6: Table 6 - Control field formats - modulo 32 768 operation Control field format I format O ISOIIEC Control f
33、ield bits I First two octets I Next two octets I I N(S) = transmitter send sequence number (bit 2 = low-order bit) N(R) = transmitter receive sequence number (bit 18 = low-order bit) S = supervisory function bit M = modifier function bit P/F P = poll bit (1 = Poll) = poll bit when issued as a comman
34、d; final bit when issued as a response (1 = PolVFinal) 4 O ISOAEC STDBISO 777b-ENGL 3775 4853703 Ob7bALLi 237 ISOhEC 7776:1995/Amd.l: 1996(E) Page 8 Subclause 4.1.1.3 Replace the last sentence with the following: The unnumbered frames shall have the same control field length (one octet) in the basic
35、 (modulo 8) operation, extended (modulo 128) operation and modulo 32 768 operation. Page 8 Subclause 4.1.2.1 Replace the last sentence with the following: The modulus equals 8, 128 or 32 768 and the sequence numbers cycle through the entire range. Page 9 Subclause 4.1.2.2.1 Replace the last sentence
36、 with the following: The value of k is defined in 5.8.4. Page 9 Subclause 4.1.2.2.4 Replace with the following: All I frames and supervisory frames, except SREJ frames with F bit set to “O“, shall contain N(R), the expected sequence number of the next received I frames. Prior to transmission of a fr
37、ame of the above types of the DTE, the value of N(R) shall be set equal to the current value of the DTE receive state variable. N(R) indicates that the transmitter of the N(R) has correctly received all I frames numbered up to N(R) - 1 inclusive. Page 9 Subclause 4.3 Replace with the following: The
38、commands and responses supported by the DTE are represented in table 7 for basic (modulo 8) operation, table 8 for extended (modulo 128) operation and table 9 for modulo 32 768 operation. For purposes of this International Standard, those encodings of the modifier function bits in tables 4, 5 and 6
39、not identified in tables 7, 8 and 9 are identified as “undefined or not implemented“ command and response control fields. The commands and responses in tables 7, 8 and 9 are defined as follows“ 5 STD-ISO 777b-ENGL 1775 4853703 Ob9b815 173 Information transfer I (information) ISOAEC 7776:1995/Amd.l:
40、1996(E) O N(S) I p I N(R) O ISO/IEC RR (receive ready) RNR(receivenotready) REJ (reject) Page 9- 1 O RR (receive ready) 1 O O O O O O O PIF N(R) RNR(receivenotready) 1 O 1 O O O O O P/F N(R) REJ (reject) 1 O O 1 O O O O P/F N(R) SREJ (selective 10110000 F N(R) Renumber Tables 5 and 6 as Tables 7 and
41、 8. Replace Table 8 with the following. Insert the following new Table 9: DISC (disconnect) Table 8 - Commands and resDonses - Extended (modulo 128) operation 11OOPO10 UA (unnumbered acknowledgement) 1100F110 DM(disconnectedmode) 1 1 1 1 F O O O FRMR (frame reject) 111OFOO1 I I Encoding 1 2 3 4 5 6
42、7 8 9 lot016 Responses Format Commands Supervisory . I reject) Unnumbered I SABME (set asvnchronous I I balanced mode-extended) I Il 111 1IPI1 1 o1 Table 9 - Commands and responses - modulo 32 768 operation Page 11 Insert a new subclause 4.3.5 as follows and renumber all subclauses that follow: 4.3.
43、5 Selective reject (SREJ) response The selective reject, SREJ, frame shall be used by a DTE to request retransmission of one or more (not necessarily contiguous) I frames. The N(R) field of the control field of the SREJ frame shall contain the sequence number of the earliest I frame to be retransmit
44、ted and the information field shall contain the sequence numbers of additional I frame(s), if any, in need of retransmission. (The DTE shall create a list of sequence numbers N(X), N(X+l), N(X+2), N(Y), N(Z+3), N(Z+4), . , N(S)-1, where N(X) is greater than or equal to V(R) and none of the I frames
45、N(X) to N(S-1) have been received. The N(R) field of the SREJ frame shall be set to N(X) and the information field set to the list N(X)+l, ., N(S)-1.) 6 STD.IS0 777b-ENL 1995 4851903 ObbBLb OOT Flag F o1 11 11 10 O ISOAEC Address Control Information FCS Flag A C I FCS F 8-m 16-bit N-bits 16-bits 01
46、1 11 11 0 ISOIIEC 7776:1995/Amd.l: 1996(E) For extended (modulo 128) operation, the information field shall be encoded such that there is an octet for each standalone I frame in need of retransmission, and a two-octet span list for each sequence of two or more contiguously numbered I frames in need
47、of retransmission, as depicted in table 10. In the case of standalone I frames, the sequence number of each designated I frame shall occupy bit positions 2-8 of an octet, with bit position 1 set to zero, as depicted in table 10. In the case of span lists, the sequence number of the first designated
48、I frame in need of retransmission is encoded in the first octet (of the two octet field for span lists) and the second octet contains the sequence number of the last designated I frame in the sequence in need of retransmission. Sequence numbers in both octets are encoded in bits 2-8 with the bit pos
49、ition 1 in both octets set to 1 as depicted in table 10. Table 10 - Control and Information field encoding of SREJ frame - Extended (modulo 128) operation T Sequence number of last I frame in span list to be retransmitted Sequence number of standalone I frame to be retransmitted Sequence number of first I frame in span list to be retransmitted Sequence number of standalone I frame to be retransmitted For modulo 32 768 operation, the information field shall be encoded such that there are two octets for each standalone I frame in need of retransmission, and a
