CAN CSA-ISO IEC 7776A-2006 Information Technology - Telecommunications and Information Exchange between Systems - High-Level Data Link Control Procedures - Description of the X 25 N.pdf

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1、Amendment 1:2006 toNational Standard of CanadaCAN/CSA-ISO/IEC 7776-96Amendment 1:1996 to International Standard ISO/IEC 7776:1995 has been adopted without modification(IDT) as Amendment 1:2006 to CAN/CSA-ISO/IEC 7776-96. This Amendment was reviewed by the CSATechnical Committee on Information Techno

2、logy (TCIT) under the jurisdiction of the Strategic SteeringCommittee on Information Technology and deemed acceptable for use in Canada.December 2006ISO/IEC 7776: 1995/Amd. 1: 1996( E) Foreword ISO (the international Organization for Standardization) and IEC (the International Electrotechnical Commi

3、ssion) form the specialized System for worldwide standardization. National bodies that are members of ISO or IEC participate in the development of International Standards through technical committees established by the respective organization to deal with particular fields of technical activity. ISO

4、 and IEC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information technology, ISO and IEC have established a joint technical committee, lSO

5、/IEC JTC 1. Draft International Standards adopted by the joint technical committee 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

6、was prepared by Joint Technical Committee lSO/IEC JTC 1, Information technology, Subcommittee SC 6, Telecommunications and information exchange between Systems. 0 ISO/IEC 1996 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by

7、 any means, electronie or mechanical, including photocopying and microfilm, without Permission in writing from the publisher. lSO/IEC Copyright Office l Case postale 56 l CH-l 211 Geneve 20 l Switzerland Printed in Switzerland ii 0 ISOAEC Introduction ISOAEC 7776:lggUAmd.l: 1996(E) This amendment to

8、 ISOAEC 7776:1995 adds the multi-selective reject Option (Option 3.3) and modulo 32 768 (Option 10.2) from ISOAEC 7809:1993. This amendment enhances ISOAEC 7776:1995 in the following areas: l it allows more efficient recovery of errored or lost I frames by selectively requesting retransmissions of o

9、ne or more I frames with a Single request; this improved efficiency is especially beneficial over links that have high data rates or large propagation delays. l link efficiency is improved by retransmitting only errored or received I frames are saved by the DTE for deferred delivery; l al lows for a

10、 much larger Ia rge propagation delays; l the maximum minus 1; modulo for Operation over links that have high data rates or r of outsta .nding lost I f rames; k tan be as large as the modulus number correctly l the additional procedures are fairly simple to implement. This page intentionally left bl

11、ank lSO/IEC lSO/lEC 7776:1995/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: Modul0 32 768 and multi-selective reject Option

12、Page 1 Clause 1 eplace Paragraph 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 ISO/lEC balanced asynchronous class of procedure with opti

13、onal functions 2 and 8 (BAC, 2, 8). Extended (modulo 128) Operation is the ISO/IEC balanced asynchronous class of procedure with optional functions 2, 8, and 10.1 (BAC, 2, 8, 10.1) or 3.3, 8 and IO. 1 (BAC, 3.3, 8, 10.1). Modul0 32 768 Operation is the ISO/IEC balanced asynchronous class of procedur

14、e with optional functions 3.3, 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-w

15、ith-span-list recovery mechanism 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 Operat

16、ion may optionally be supported - 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 DTE/DCE connections that support basic (modulo 8) Operation, extended (modulo 128) Operation and/or

17、modulo 32 768 Operation, the choice of modulo and, when applicable, recovery mechanism is made at subscription-time only. For those DTE/remote DTE connections that support basic (modulo 8) Operation, extended (modulo 128) Operation and/or modulo 32 768 Operation, the choice of modulo and, when appli

18、cable, recovery mechanism is made by bilateral agreement. NOTE - The procedure herein described as basic (modulo 8) Operation is the only one available in all public data networks. Page 7 Clause 1 epiace Paragraph 4 with the following: ISO/lEC 7776:1995/Amd.l: 1996(E) 0 ISO/IEC Clause 4 describes th

19、e 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. Page 2 Clause 3 eplace Paragraph 1 with the following: All transmissions on a SLP are in frames conforming to one of the for

20、mats of table 1 for basic (modulo 8) Operation, or one of the formats of table 2 for extended (modulo 128) Operation or alternatively one of the formats of table 3 for modulo 32 768 Operation. The flag preceding the address field is defined as the openina flaa. The flag following the FCS field is de

21、fined as the closing flag. Page 3 Clause 3 Add the following new Table 3, and renumber all the other tables that follow: Table 3 - Frame formats - modulo 32 768 Operation Bit Order of transmission 12345678 12345678 1 to * 16tol 12345678 c Flag Address Control FCS Flag F A C FCS F 01111110 * 8-bits -

22、bits 16-bits 01111110 FCS = Frame Check Sequence Bit Order of transmission 12345678 12345678 1 to * 16tol 12345678 Flag Address Control Information FCS Flag F A C I FCS F 01111110 * 8-bits -bits N-bits 16.bits 01111110 FCS = Frame Check Sequence * 32 for frame formats that contain sequence numbers;

23、8 for frame formats that do not contain sequence numl Page 3 Subclause 3.3 Paragraph 1, eplace 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 that c

24、ontain 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 conten

25、t of this field is described in 4.1. 2 0 ISOAEC ISO/IEC 7776:1995/Amd.l: 1996(E) Page 3 Subclause 3.4, Paragraph 1, Line 2: Change 4.3.9 to 4.3.10 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 Replace Paragraph 3 with the following: The FCS sh

26、all be transmitted to the Iine 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 “ 15” . Page 7 Subclause 3.11.2.2 Change 5.7.1.5 to 5.8.1.5. Page 7 Subclause 3.11.2.2, Note Cha

27、nge 5.7.7.3 to 5.8.7.3. Page 7 Subclause 4.1 .l Replace the second Paragraph with the following: Three types of control field formats are used to perform numbered information transfer (1 format), number supervisory functions (S format) and unnumbered control functions (U format). The control field f

28、ormats 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 ISO/lEC 7776:1995/Amd.l: 1996(E) 0 ISOAEC Page 8 Renumber Tables 3 and 4 a

29、s Tables 4 and 5 and insert the following new Table 6: Table 6 - Control field formats - modulo 32 768 Operation Control field format Control field bits First two octets Next two octets 12 8 I format 0 . NW S format 1 ossxxxxx. 16 17 18 P/F x P/F 32 N(R) * N(R) U format 111 MMP/FMMMI N(S) = transmit

30、ter 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 = pell bit when issued as a command; final bit when issued as a response (1 = PoWFinal) P = pell bit (1 = Pall) o ISO/IEC IS

31、O/lEC 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 (modulo 8) Operation, extended (modulo 128) Operation and modulo 32 768 Operation. Page 8 Subclause 4.1.2.1 R

32、eplace the last sentence with #he fol/owing: . 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 with the following: The value of k is defined in 5.8.4. Page 9 Subclause 4.1.2.2.4 Replace with the followi

33、ng: 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 frame of the above types of the DTE, the value of N(R) shall be set equal to the current value of the DTE re

34、ceive 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 commands and responses supported by the DTE are represented in table 7 for basic (modulo 8) Operation, tab

35、le 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 not identified in tables 7, 8 and 9 are identified as “ undefined or not implemented” command and response

36、 control fields. The commands and responses in tables 7, 8 and 9 are defined as follows” lSO/lEC 7776:1995/Amd.l: 1996(E) 0 ISOAEC Page 9-10 Renumber Tables 5 and 6 as Tables 7 and 8. Replace Table 8 with the following. Insert the following new Table 9: Table 8 - Commands and responses - Extended (m

37、odulo 128) Operation Format Commands Responses Encoding 1 2 3 4 5 678 9 lOtol6 Information transfer 1 I (information) I I I 0 N(S) I p I N(R) I Supervisory RR (receive ready) RNR (receive not ready) REJ (reject) . RR (receive ready) RN R (receive not ready) REJ (reject) SREJ (selective reject) 1 0 0

38、 0 0 0 0 0 P/F WR) 1 0 1 0 0 0 0 0 PIF WR) 1 0 0 1 0 0 0 0 PIF N(R) 1 0 1 1 0000 F N(R) . Unnumbered SABME (set asynchronous baianced mode extended) 11 Ill ,/Pi1 1 01 1 DISC (disconnect) I 1 110 OIPIO 1 01 UA (unnumbered acknowledgement) 1 1 OOFIIO DM (disconnected mode) 1 1 1 1 F 0 0 0 FRMR (frame

39、reject) 1 1 1 0 F 0 0 1 Table 9 - Commands and responses - modulo 32 768 Operation Format Information transfer Supenrisory Unnumbered Commands I (information) RR (receive ready) RNR (receive not ready) SM (set mode) DISC (disconnect) Responses RR (receive ready) RN R (receive not ready) SREJ (select

40、ive reject) UA (unnumbered acknowledgement) DM (disconnected mode) FRMR (frame reject) Encoding 1 2 3 4 5 .8 . 16 17 18to32 1 0 I N(S) / p 1 N(R) I 1 0000 0 00 PIF N(R) 10100 0 00 P/F N(R) 10110 000 F N(R) 1 1 0 0 P Oll 1 1 0 0 P 010 1 1 0 0 F 110 1 1 1 1 F 000 1 1 1 0 F 001 Page 11 Insert a new sub

41、clause 4.3.5 as follows and renumber all subclauses that follow: 4.3.5 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

42、 contain the sequence number of the earliest I frame to be retransmitted 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)

43、-1, where N(X) is greater than or equal to V(R) and none of the I frames 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 0 ISOAEC lSO/lEC 7776:1995/Amd.l: 1996(E) For extended (modulo 128)

44、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 of retransmission, as depicted in table 10. In the case of standalone

45、 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 I frame in need of retransmission is encoded in the first octet (of t

46、he 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 Position 1 in both octets set to 1 as depicted in table 10. Table 10 - C

47、ontrol and Information field encoding of SREJ frame - Extended (modulo 128) Operation 12345678 12345678 1 to16 16to 1 12345678 Flag Address Control Information FCS Flag F A C I FCS F 01111110 8-bits 16-bits N-bits 16.bits 01111110 iiY/ 345678 12345678 12345678 0110000 F: N(R) i l N(R) 1 : . N(R) 1 :

48、. . N(R) 0: . N(R) 1 %= . . l Sequence number of standalone I frame to be retransmitted / Sequence number of last I frame in span list to be retransmitted 1 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 O

49、peration, the information field shall be encoded such that there are two octets for each standalone I frame in need of retransmission, and a four-octet span list for each sequence of two or more contiguously numbered I frames in need of retransmission, as depicted in table 11. In the case of standalone I frames, the sequence number of each designated I frame shall occupy bit positions 2-16 of the two octet field, with bit Position 1 set to Zero, as depicted in table 11. In the case of span lists, the sequence number of the first designated I frame in need of retransmission is encoded in