1、BRITISH STANDARD BS ISO/IEC 8878:1992 Incorporating Amendment No. 1 Information technology Telecommunications and information exchange between systems Use of X.25 to provide the OSI Connection-mode Network Service ICS 35.100.30 UDC 681.3:621.39BSISO/IEC8878:1992 This British Standard, having been pr
2、epared under the directionof the Information Systems Technology Standards Policy Committee, was publishedunder the authorityofthe Standards Boardand comes into effect on 15 November 1993 BSI 06-1999 The following BSI references relate to the work on this standard: Committee reference IST/6 Draft for
3、 comment 90/65970 DC ISBN 0 580 22608 5 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Information Systems Technology Standards Policy Committee (IST/-) to Technical Committee IST/6, upon which the following bodies were represented: Bri
4、tish Computer Society British Telecommunications plc CCTA (the Government Centre for Information Systems) Digital Equipment Co Ltd. IBM United Kingdom Ltd. Information Systems Committee of the Universities Funding Council Institute of Electrical Engineers International Computers Limited Logica UK Lt
5、d. Ministry of Defence Rank Xerox Ltd. Swift Project Consortium Amendments issued since publication Amd. No. Date Comments 9675 December 1997 Indicated by a sideline in the marginBSISO/IEC8878:1992 BSI 06-1999 i Contents Page Committees responsible Inside front cover National foreword ii Foreword v
6、Text of ISO/IEC 8878 1BSISO/IEC8878:1992 ii BSI 06-1999 National foreword This British Standard reproduces verbatim ISO/IEC8878:1992 (incorporating Technical Corrigendum 1:1993, Technical Corrigendum 2:1993 and Technical Corrigendum 3:1996) and implements it as the UK national standard. This British
7、 Standard supersedes BS7224:1990 which is withdrawn. This British Standard is published under the direction of the Information Systems Technology Standards Policy Committee whose Technical Committee IST/6 has the responsibility to: aid enquirers to understand the text; present to the responsible int
8、ernational committee any enquiries on interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. NOTEInternational and European Standards, as well as overseas standards, are available from Customer S
9、ervices, Publications, BSI, Linford Wood, Milton Keynes, MK146LE. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity
10、 from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi and ii, theISO/IEC title page, pages ii to vi, pages1to80 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indica
11、ted in the amendment table on the inside front cover.ISO/IEC8878:1992(E) ii BSI 06-1999 Contents Page Foreword v Introduction 1 1 Scope 2 2 Normative references 3 2.1 Identical Recommendations|International Standards 3 2.2 Paired Recommendations|International Standards equivalent in technical conten
12、t 3 2.3 Additional references 3 3 Definitions 4 3.1 Reference Model definitions 4 3.2 Service Conventions definitions 4 3.3 Network Service definitions 4 3.4 X.25 definitions 4 3.5 X.96 definitions 4 4 Abbreviations 5 4.1 Network Service abbreviations 5 4.2 X.25 abbreviations 5 5 Overview 5 5.1 Elem
13、ents of the X.25/PLP-1984 used to support the OSI CONS 5 5.2 General operation of the X.25/PLP-1984 for supporting the OSI CONS 7 6 Network connection establishment phase 8 6.1 Primitive/Parameter and packet/field relationships 8 6.2 Procedures 8 7 Network connection release phase 16 7.1 Primitive/P
14、arameter and packet/field relationships 16 7.2 Procedures 16 8 Data transfer phase Data transfer service 18 8.1 Primitive/Parameter and packet/field relationships 18 8.2 Procedures 18 9 Data transfer phase Receipt confirmation service 19 9.1 Primitive and packet/field relationships 19 9.2 Procedures
15、 19 10 Data transfer phase Expedited data transfer service 19 10.1 Primitive/Parameter and packet/field relationships 19 10.2 Procedures 19 11 Data transfer phase Reset service 20 11.1 Primitive/Parameter and packet/field relationships 20 11.2 Procedures 20 12 Response to protocol violations 21 13 C
16、onformance 22 13.1 Conformance requirements 22 13.2 Optional features 23 Annex A (normative) X.25 (1980) Subnetwork Dependent Convergence Protocol 24 A.1 Introduction 24 A.2 Scope 24 A.3 Abbreviations 25 A.4 Overview of the protocol 25 A.5 Protocol mechanisms 27 A.6 Protocol description 37ISO/IEC887
17、8:1992(E) BSI 06-1999 iii Page A.7 Protocol encoding in X.25 packets 47 Annex B (normative) Classification 51 B.1 Classification of systems 51 B.2 Functionality of classes 52 B.3 Scenarios 52 B.4 Procedures for selecting class of operation 52 B.5 Interworking by relay system 52 Annex C (normative) S
18、ubnetwork Convergence Protocol for Use WithX.25Permanent Virtual Circuits 54 C.1 Introduction and scope 54 C.2 Overview 54 C.3 Abbreviations 55 C.4 Protocol mechanisms 55 C.5 Protocol encoding for NC establishment and release 56 Annex D (normative) Protocol Implementation Conformance StatementProfor
19、ma 58 D.1 Introduction 58 D.2 Scope 58 D.3 Normative references 58 D.4 Definitions 58 D.5 Abbreviations 58 D.6 Protocol Implementation Conformance Statement Proforma 59 D.7 Modified PICS requirements for ISO/IEC 8208 68 Annex E (informative) Additional Considerations of CONS Primitives 73 E.1 Introd
20、uction 73 E.2 Environment for X.25/PLP operation 73 Annex F (informative) Use of X.25/PLP NPAI 75 F.1 Introduction 75 F.2 Obtaining an SNPA address 75 F.3 Examples of Network Address encoding 75 Annex G (informative) Transit Delay Calculations 77 Annex H (informative) Example of Priority Negotiation
21、 78 Annex I (informative) Differences between Recommendation X.223 and ISO/IEC 8878 79 Figure 1 Relationship of the X.25 Packet Layer Protocol to the OSIConnection-Mode Network Service 2 Figure 2 Operation of OSI Connection-Mode Network Service and X.25PacketLayer Protocol (1984) 7 Figure A.1 State
22、transition diagram 38 Figure A.2 Message sequence charts 43 Figure B.1 Procedure for selecting class of operation 53 Figure B.2 Operation of a relay system mapping between the X.25/PLP-1984 and the X.25/PLP-1980 with SNDCP 54 Figure C.1 Call setup/clearing encoding 57 Table 1 Packets and fields of t
23、he X.25/PLP-1984 used to support the OSICONS 6 Table 2 CONS:X.25/PLP-1984 mapping for the NC establishment phase 8ISO/IEC8878:1992(E) iv BSI 06-1999 Page Table 3 Mapping of Throughput QOS subparameters to X.25/PLP-1984 Facilities 11 Table 4 CONS:X.25/PLP-1984 mapping for the NC release phase 16 Tabl
24、e 5 CONS:X.25/PLP-1984 mapping for the data transfer service 18 Table 6 CONS:X.25/PLP-1984 mapping for the Expedited Data TransferService 20 Table 7 CONS:X.25/PLP-1984 mapping for the Reset Service 20 Table A.1 Mapping for NC establishment phase 28 Table A.2 Mapping for NC Release phase 29 Table A.3
25、 Mapping of NS Disconnect Reason to X.25 Diagnostic Code 31 Table A.4 Mapping of X.25 Clearing/Restarting Cause to NS Reason 33 Table A.5 Mapping for Data Transfer phase 34 Table A.6 Mapping of NS Reset Reason to X.25 Diagnostic Code 34 Table A.7 Mapping of X.25 Reset Cause to NS Reason 34 Table A.8
26、 Mapping of Throughput QOS subparameters to X.25 (1980) facilityand SNDCP parameter 35 Table A.9 State/Event table for NC establishment phase 39 Table A.10 State/Event table for data transfer phase 41 Descriptors: Data processing, telecommunications, information interchange, network interconnection,
27、 open systems interconnection, data transmission, communication procedure, control procedures, network service.ISO/IEC8878:1992(E) BSI 06-1999 v Foreword ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the specialized system for w
28、orldwide 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 and IEC technical committees collaborat
29、e 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, ISO/IECJTC1. Draft International Standards
30、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. International Standard ISO/IEC8878 was prepared by Joint Technical Committee ISO/IECJTC1, Informati
31、on technology. This second edition cancels and replaces the first edition (ISO8878:1987), which has been technically revised. It consolidates Technical Corrigenda 1, 2 and3, Addenda1 and2 and Amendment1 as well as Technical Corrigendum1 toAddendum2. NOTEISO/IEC DIS8878-2 as well as defect reports 88
32、78-012, 013, 014 and015 have also been included in this second edition. Annex A, Annex B, Annex C andAnnex D form an integral part of this International Standard. Annex E, Annex F, Annex G, Annex H andAnnex I are for information only.vi blankISO/IEC8878:1992(E) BSI 06-1999 1 Introduction This Intern
33、ational Standard defines methods for providing the OSI Connection-Mode Network Service (CONS) through the use of the virtual circuit services of theX.25 Packet Layer Protocol(X.25 PLP). The method presented in the main body of this International Standard specifies a mapping between elements of the19
34、84 or later versions of theX.25/PLP (referred to asX.25/PLP-1984) usingX.25 Virtual Call (VC) services and elements of the OSI CONS. Features associated with versions ofX.25 later than1984 are identified as to which version they relate. This International Standard is similar to CCITTRecommendationX.
35、223; however, the two are currently published as separate documents. Clause13 contains the requirements for systems claiming conformance to this International Standard. Other methods using other virtual circuit services and/or other versions ofX.25 are also defined. In particular, a second method fo
36、r VCs, which is presented inAnnex A, defines a Subnetwork Dependent Convergence Protocol (SNDCP) that shall be used to provide the OSI CONS over subnetworks or with equipment using the1980 or earlier versions of theX.25/PLP (referred to asX.25/PLP-1980). This SNDCP should only be used if the element
37、s of the X.25/PLP-1984, as defined in5.1 herein, are not available to support the OSI CONS. Annex B contains a classification of systems according to whether they implement the procedures defined in the main body of this International Standard, the procedures defined in Annex A, or both. In addition
38、, it describes the possibilities and the rules for interworking between the classes of equipment identified. Annex A andAnnex B are integral parts of this International Standard. They are intended to provide a migration strategy towards the use of the1984 version ofX.25 in both subnetworks and DTEs.
39、 Because of the evolution of technology, the status ofAnnex A andAnnex B will be reviewed in the future. Annex C defines another method for providing the OSI CONS, in this case in conjunction with the PVC service of X.25. Annex D provides the Protocol Implementation Conformance Statement (PICS) Prof
40、orma for this International Standard. Annex C andAnnex D are integral parts of this International Standard. Annex E provides additional considerations on the relationship between the X.25 protocol procedures and the CONS primitives. Annex F illustrates the use ofX.25 Network Protocol Address Informa
41、tion (NPAI), i.e., the Address Field and the Address Extension Facilities. Annex G illustrates the use of theX.25 transit delay facilities. Annex H illustrates the use of theX.25 Priority Facility. Annex I lists the differences between CCITTRec.X.223 and ISO/IEC8878. Annex E throughAnnex I are not i
42、ntegral parts of this International Standard. The relationship between the X.25/PLP-1984 and the OSI CONS is shown inFigure 1. This relationship is described only in terms of the Network Layer entities that provide the CONS. No discussion is given here to describe the actions of a Network Layer enti
43、ty that only provides a relay function for a given network connection. The OSI Network Service is defined in terms of a) the primitive actions and events of the Service; b) the parameters associated with each primitive action and event, and the form which they take; c) the interrelationship between,
44、 and the valid sequences of, these actions and events. The OSI Network Service does not specify individual implementations or products nor does it constrain the implementation of entities and interfaces within a computer system. The X.25/PLP-1984 is defined in terms of a) procedures for Virtual Call
45、s and Permanent Virtual Circuits; b) formats of packets associated with these procedures; c) procedures and formats for optional user facilities and CCITT-Specified DTE facilities.ISO/IEC8878:1992(E) 2 BSI 06-1999 The use of the word “Network” to name the “Network” Layer of the OSI Reference Model s
46、hould be distinguished from the use of the word “network” to denote a communications network as conventionally understood. To facilitate this distinction, the term “subnetwork” is used for a collection of physical equipment, commonly called a “network” (reference CCITT Rec. X.200|ISO7498). Subnetwor
47、ks may be either public or private networks. In the case of public networks, their properties may be determined by separate CCITT Recommendations such as CCITT Rec.X.21 for a circuit-switched network or CCITTRec.X.25 for a packet-switched network. Throughout the set of OSI-related Recommendations|In
48、ternational Standards, the term “Service” refers to the abstract capability provided by one layer of the OSI Reference Model to the layer above it. Thus, the Network Service is a conceptual architectural Service, independent of administrative divisions. NOTEIt is important to distinguish the special
49、ized use of the term “Service” within the set of OSI-related Recommendations|International Standards from its use elsewhere to describe the provision of a service by an organization (such as the provision of a service, as defined in CCITT Recommendations, by an Administration). 1 Scope The OSI Connection-mode Network Service (CONS) is defined in terms of a set of primitive actions and events and associated parameters. For a protocol to support this service, there must be a mapping between the abstract primitives
