1、 8883 89 = 4853903 0305973 9 = . I- INTERNATIONAL STANDARD ISO/IEC 8881 : 1989 TECHNICAL CORRIGENDUM 1 _ - - Published 1991-05-15 I INTERNATIONAL ORGANIZATION FOR STANDARDIZATION. MEXAYHAPOAHAR OPrAHM3AL(MA FIO CTAHAAPTM3AL(MM* ORGANISATION INTERNATIONALE DE NORMALISATION INTERNATIONAL ELECTROTECHNI
2、CAL COMMISSION MEXAYHAPOAHAR 3ilEKTPOTEXHM-lECWR KOMMCCMR - COMMISSION ELECTROTECHNIQUE INTERNATIONALE Information processing systems - Data communications - Use of the X.25 packet level protocol in local area networks TECHNICAL CORRIGENDUM 1 Systmes de traitement de linformation - Communication de
3、donnes - Emploi du protocole X.25 au niveau paquet dans des rseaux locaux RECTIFICA TIF TECHNIQUE 1 Technical corrigendum 1 to International Standard ISO/IEC 8881 : 1989 was prepared by ISO/IEC JTC 1, Information technology. Page 1 Subclause 3.3 Add the following: “e) DSAP f) SSAP“ Clause 4 Insert i
4、n alphabetical order the following : “DSAP Destination Service Access Point SSAP Source Service Access Point“ Page 2 Clause 5 Add a second paragraph as follows: “The use of the X.25 PLP on a LAN shall be identified by setting the value of both the DSAP and SSAP addresses to “XII 1 1110“.“ UDC 681.3
5、: 621.39 Ref. No. ISOllEC8881 : 19891Cor.l : 1991 (E) Descriptors: data processing, data transmission, network interconnection, open systems interconnection, local area networks, data terminal equipment, communication procedure, control procedures. O ISO/IEC 1991 Printed in Switzerland Information p
6、rocessing systems - Data communications - Use of the X.25 packet level protocol in local area networks Systmes de traitement de iinforrnation - Communication de donnes - Emploi du protocole X.25 au niveau paquet dans des rseaux locaux Reference number ISO/IEC 8881 : 1989 (E) 8883-89 1485903 0079625
7、8 ISO/IECI : 1989 (E) Contents Page Foreword ,. , . , . , , , , , , , , , . , , , , , . , , . , , , , , , . . , . , , , . . . . . , . . . . . . . . . . . . . . . . . . . , , , . , . , . . . . , . , , , . Introduction . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . , .
8、 . . . . . . . . . , . , . Section 1 : General 1 Scope . . . . , . . . . . . . . , . . . . . , , , . . . . , . . . . . . . , . . . . . . . . . . . . . . . . , . . . . , . , . , , . . . , , . . . . , . . . . . 1 2 Normative references . . , , . . . , . . . . , . . . , . . . . . , . , . . . . . . . .
9、. . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 Definitions,. . . , . . , . , . , , . . , , . . . . . . , . . , . , , . . , , . , . . , , , . . . . . . , . . , , , , . , , . . . , , , , . , . . . . . . . , , . . 1 4 Abbreviations . . , , . . . . . . . . . . . . . . . , ,. . . . . . , . . .
10、 . . , . , , . . . . . . . . . , . . . . . , . . . , . . 1 5 Underlying layer considerations . , . . . . , . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 Packet Level considerations . . . . , , , ,. , . , . . . . . . . . . . . . . , , . . . . . . . , . . . . . . . .
11、. . 2 Section 2 : Operation with LLC Type 2 procedures 7 System parameters . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 8 Startup operation . ., . ,. , . 3 Section 3 : Operation with LCC Type 1 procedures 9 Applicabil
12、ity of LLC Type 1 procedures . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 10 System parameters . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . 4 11 Startup operation . . . . . . 4 12 Using the broa
13、dcast capability,. . . . . , . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Section 4 : Conformance requirements 13 Conformance ,. , , , , , . . , , , . . . . , . . . . . . . . . . . . . . . . , , , . . . . . . . . . . . . . . . . . , . . . . . . . . . . , , . ,
14、, . i iv 6 O ISO/IEC 1989 All rights 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 publisher. Printed in Switzerland ISOIIEC Copyright Office o Ca
15、se postale 56 0 CH-1211 Genve 20 0 Switzerland Foreword IS0 (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) together form a system for worldwide standardization as a whole. National bodies that are members of IS0 or IEC participate in the
16、develop- ment of International 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 international organizations, governmental and non-go
17、vernmental, 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/IEC JTC 1. Draft International Standards adopted by the joint technical committee are circulated to national bodies for approval
18、before their accep- tance as International Standards. They are approved in accordance with procedures re- quiring at least 75 % approval by the national bodies voting. International Standard ISO/IEC 8881 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology. iii 8881-89 Bq8
19、51903 0077b27 1 ISO/IEC 8881 : 1989 (E) Introduction IS0 8802 specifies the Medium Access Control (MAC) and Logical Link Control (LLC) procedures for accessing a Local Area Network (LAN). This International Standard specifies the use of the X.25 Packet Level Protocol (PLP) (both X.25/PLP:1980 and X.
20、25/PLP:1984), as specified in IS0 8208, to provide additional capabilities beyond those available using the MAC and LLC procedures. These additional capabilities include the ability to support the OS1 Connection- mode Network Service in a LAN station, as specified in IS0 8878, and the ability to att
21、ach terminals to a LAN station acting as a Packet Assembly/Disassembly Facility (see, for example, CCIT Recommendations X.3, X.28, and X.29). The X.25 PLP provides several functional capabilities that include, but are not limited to a) multiplexing -the ability to support multiple data streams; b) t
22、ransfer of addressing information - the ability to transfer addressing information, including OS1 Network Service Access Point addresses: c) segmenting and reassembly - the ability to divide a data unit into smaller packets for transfer over a LAN and to reassemble packets into the original data uni
23、t; d) flow control - the ability to control, for each data stream, the flow of data between transmitting and receiving Data Terminal Equipment (DTE); e) transfer of expedited data - the ability to transfer a small amount of data outside the normal flow-control procedures; f) error control -the abili
24、iy to detect errors at the Packet Level: and g) reset and restart - the ability to reinitialize communication paths at the Packet Level in the event that non-recoverable error conditions are encountered. When using the X.25 PLP within a LAN, the X.25 PLP operates in the point-to- point (DTE-to-DTE)
25、mode without an intervening packet-switched network. The LAN station operates one Packet Level Entity for each DTUDTE interface (.e, for each station with which it communicates). ISO/IECTTR 10029 describes the operation of an interworking unit to connect an X.25 Packet Level Entity in a LAN station
26、to another X.25 Packet Level Entity. iv INTERNATIONAL STANDARD ISO/IEC 8881 : 1989 (E) Information processing systems - Data communications - Use of the X.25 packet level protocol in local area networks Section 1: General 1 Scope This International Standard deals with the use of the X.25 Packet Leve
27、l Protocol (PLP) as specified in IS0 8208 operating over IS0 8802 Local Area Networks (LANs). Section 2 of this International Standard specifies the operation of the X.25/PLP using the Logical Link Control (LLC) Type 2 procedures defined in IS0 8802-2. Section 3 of this International Standard specif
28、ies the operation of the X.25/PLP using the LLC Type 1 procedures defined in IS0 8802-2. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated w
29、ere valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards listed below. Members of IEC and IS0 maintain registers of currently valid Internationa
30、l Standards. IS0 74983 984, Information processing systems - Open Systems Interconnection - Basic Reference Model. IS0 8208:1987, Information processing systems - Data communications - X.25 Packet Level Protocol for Data Terminal Equipment. IS0 8208/Add. 1: .,) Information processing systems - Data
31、communications - X.25 Packet Level Protocol for Data Terminal Equipment - Addendum 1: Alternative logical channel number allocation. IS0 8348/Add. 2:1988, Information processing systems - Data communications - Network service definition - Addendum 2: Network layer addressing. IS0 8802-2: .,l) Inform
32、ation processing systems - Local area networks - Part 2: bogical link control. IS0 8878:l 987, Information Processing systems - Data communications - Use of X.25 to provide the OS1 connection-mode network service. 1) To be published ISO/IECTTR 10029:1989, Information processing systems - Data cornmu
33、nications - Operation of an X.25 interworking unit. 3 Definitions 3.1 Reference Model definitions This International Standard makes use of the following terms defined in IS0 7498: a) OS1 Network Service b) OS1 Network Service Access Point address 3.2 Addressing definitions This International Standar
34、d makes use of the following term defined in IS0 8348/Add. 2: 3.3 Local Area Network definitions This International Standard makes use of the following terms defined in IS0 8802: a) Local Area Network b) Logical Link Control c) Medium Access Control d) Data Link Layer Service Access Point address 3.
35、4 X.25 Packet Level Protocol definitions This International Standard makes use of the following terms defined in IS0 8208: a) Packet Level Entity b) Virtual Call c) Logical Channel d) Lowest Incoming Channel e) Highest Incoming Channel 9 Lowest Two-way Channel g) Highest Two-way Channel h) Lowest Ou
36、tgoing Channel i) Highest Outgoing Channel a) Subnetwork Point of Attachment address 4 Abbreviations CCIlT International Telegraph and Telephone Consultative Committee DCE Data Circuit-terminating Equipment DTE Data Terminal Equipment 1 8883-89 14853903 0079629 5 I- ISO/IEC 8881 : 1989 (E) HIC HOC H
37、TC LAN LCN LIC LLC LOC LTC MAC NSAP PDU PL PLP SNPA XID Highest Incoming Channel Highest Outgoing Channel Highest Two-way Channel Local Area Network Logical Channel Number Lowest Incoming Channel Logical Link Control Lowest Outgoing Channel Lowest Two-way Channel Medium Access Control Network Servic
38、e Access Point Protocol Data Unit Packet Level Packet Level Protocol Subnetwork Point of Attachment Exchange Identification 5 Underlying layer considerations When the X.25 PLP is used in a LAN, it is used in the point-to-point (DTE-to-DTE) mode allowed by IS0 8208. In this case, each LAN station act
39、s as a DTE. The LAN station (conceptually) operates one PL Entity for each DTEiDTE interface in which it is involved (i.e., for each remote LAN station with which it communicates). Within a LAN station, the PL Entity associated with a DTE/DTE interface is identified by the Medium Access Control (MAC
40、) Address of the remote LAN station. The DTUDTE interface is thus identified by the pair of MAC Addresses of the two LAN stations associated with the interface. These concepts are illustrated in Figure 1. 6 Packet Level considerations 6.1 Logical channel number assignment In the case of DTE/DTE comm
41、unication over LANs, the task of agreeing to the ranges of logical channels available for each pair of communicating DTEs is potentially difficult. Different stations on a LAN, performing different functions I PAYSICAL AYER I I I I I I I I I I I I I I I over X.25 PLP, could have very different requi
42、rements in terms of the number of simultaneous Virtual Calls to be handled when communicating with another individual LAN station. To alleviate this problem, the following scheme is used. The LAN administration defines the logical-channel ranges (LIC, HIC, LTC, HTC, LOC, and HOC in IS0 8208) to be u
43、sed by all DTEs attached to the LAN. Note that one occurrence of the logical-channel range parameters (LIC, etc.) exists for each X.25 PL Entity in a DTE and, therefore, multiple occurrences of all logical-channel numbers (up to the number of X.25 PL Entities) can result. A DTE may then assume that
44、all logical channels within the defined ranges are available for use according to the procedures defined in IS0 8208. However, a DTE need not allocate resources for all available logical channels. A DTE receiving an INCOMING CALL packet specifying a valid LCN within the defined range but which is no
45、t capable of accepting the call due to lack of logical-channel resources shall clear the call. In this case, the cause is “DTE Originated“ and the diagnostic is “DTE Resource Constraint“ (1 63). One DTE assumes the role of a DCE for the purpose of logical-channel selection according to the procedure
46、s defined in IS0 8208. Clauses 8 and 11 below define the startup procedures to determine which DTE assumes the DCE role. The On-line Facility Registration Facility may be used by a pair of DTEs to redefine the logical-channel ranges to be used between those DTEs (i.e., to change the values of LIC, e
47、tc.). The use of this facility requires prior, bilateral agreement between the DTEs. NOTE - Following redefinition of the logical-channel ranges, the same considerations mentioned previously regarding the availability of resources to valid LCNs apply. X.25 PL ENTITY j LLC I MAC (ADDRESS=Y) PiYs icAL
48、 LAYER b) Extended Packet Sequence Numbering; c) One-way Outgoing Logical Channels; d) One-way Incoming Logical Channels; e) Nonstandard Default Packet Sizes: f) Nonstandard Default Window Sizes; g) Default Throughput Classes Assignment; h) Flow Control Parameter Negotiation; i) Throughput Class Neg
49、otiation; k) Transit Delay Selection And Indication; I) Calling Address Extension; m) Called Address Extension; n) Minimum Throughput Class Negotiation; o) End-to-end Transit Delay Negotiation; and p) Expedited Data Negotiation. For each of the facilities (e), (f), and (g), every station on the LAN should use the same value. OTE - Throughput, in the X.25 PLP sense, is a measure of the number of bits per second of user data that a higher layer entity needs to transfer over a particular virtual circuit. In turn, it implies an allocation of resources in the LAN station to
