1、BRITISH STANDARD BS ISO/IEC 8473-4:1995 Implementation of ISO/IEC 8473-4:1995 Information technology Protocolfor providingthe connectionless-mode network service: Provisionofthe underlying service by a subnetwork that provides the OSI data link serviceBSISO/IEC8473-4:1995 This British Standard, havi
2、ng been prepared under the directionof the Information Systems Technology Assembly,was published underthe authority of the Standards Board and comes intoeffect on 15 July1995 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference IST/6 Draft for comment 94/
3、642219 DC ISBN 0 580 24514 4 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Information Systems Technology Assembly (IST/-) to Technical Committee IST/6, upon which the following bodies were represented: British Computer Society British
4、 Telecommunications plc CCTA (the Government Centre for Information Systems) Digital Equipment Co Ltd. IBM United Kingdom Ltd. Institution of Electrical Engineers International Computers Limited Logica UK Ltd. Nine Tiles Computer Systems Ltd. Rank Xerox (UK) Ltd. Amendments issued since publication
5、Amd. No. Date CommentsBSISO/IEC8473-4:1995 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii Foreword iii Text of ISO/IEC 8473-4 1BSISO/IEC8473-4:1995 ii BSI 10-1999 National foreword This British Standard reproduces verbatim ISO/IEC8473-4:1995 and implements
6、 it as the UK national standard. This British Standard is published under the direction of the Information Systems Technology Assembly whose Technical Committee IST/6 has the responsibility to: aid enquirers to understand the text; present to the responsible international committee any enquiries on
7、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 Services, BSI, 389 Chiswick High Road,
8、London W4 4AL. 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 from legal obligations. Summary of pages This docu
9、ment comprises a front cover, an inside front cover, pages i and ii, theISO/IEC title page, pages ii to iv, pages 1 to 10 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front
10、cover.ISO/IEC8473-4:1995(E) ii BSI 10-1999 Contents Page Foreword iii Introduction 1 1 Scope 1 2 Normative references 1 2.1 Identical Recommendations|International Standards 1 2.2 Paired Recommendations|International Standards identical in technical content 1 2.3 Additional references 1 3 Definition
11、s 2 3.1 Reference model definitions 2 3.2 Network layer architecture definitions 2 3.3 Network layer addressing definitions 2 3.4 Data link service definitions 2 4 Abbreviations 2 5 Subnetwork dependent convergence function 3 5.1 General model 3 5.2 Subnetwork user data 3 5.3 Subnetwork dependent co
12、nvergence functions used with subnetworks that provide the OSI data link service 3 Annex A PICS proforma 6 A.1 Introduction 6 A.2 Abbreviations and special symbols 6 A.3 Instructions for completing the PICS proforma 6 A.4 Identification 8 A.5 Major capabilities 9 A.6 Subnetwork dependent convergence
13、 functions for use with subnetworks that provide the OSI connectionless Data Link service 9 A.7 Subnetwork dependent convergence functions for use with subnetworks that provide the OSI connection-mode Data Link service 9ISO/IEC8473-4:1995(E) BSI 10-1999 iii Foreword ISO (the International Organizati
14、on for Standardization) and IEC (the International Electrotechnical Commission) 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 respecti
15、ve organization to deal with particular fields of technical activity. ISO 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
16、technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC1. 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 least75% of the national bodies ca
17、sting a vote. International Standard ISO/IEC8473-4 was prepared by Joint Technical Committee ISO/IEC JTC1, Information technology, Subcommittee SC6, Telecommunications and information exchange between systems, in collaboration with ITU-T. The identical text is published as ITU-T Recommendation X.623
18、. ISO/IEC 8473 consists of the following parts, under the general title Information technology Protocol for providing the connectionless-mode network service: Part 1: Protocol specification; Part 2: Provision of the underlying service by an ISO/IEC 8802 subnetwork; Part 3: Provision of the underlyin
19、g service by an X.25 subnetwork; Part 4: Provision of the underlying service by a subnetwork that provides the OSI data link service. Annex A forms an integral part of this part of ISO/IEC8473.iv blankISO/IEC8473-4:1995(E) BSI 10-1999 1 Introduction This is one of a set of Recommendations and Intern
20、ational Standards produced to facilitate the interconnection of open systems. The set covers the services and protocols required to achieve such interconnection. This Recommendation|International Standard ispositioned with respect to other related Recommendations and International Standardsbythe lay
21、ers defined in ITU-T Rec. X.200|ISO/IEC7498-1. In particular, itdefines the way in which an X.25 subnetwork maybe used within the Network layer to providethe abstract underlying service with respectto which the protocol defined by ITU-TRec.X.233|ISO/IEC8473-1 is specified. In order to evaluate the c
22、onformance of a particular implementation of this protocol, it is necessary to have a statement of which of the protocols capabilities and options have been implemented. Such a statement is called a Protocol Implementation Conformance Statement (PICS), as defined in CCITT Rec. X.290|ISO/IEC9646-1. A
23、 PICS proforma, from which a PICS may be prepared for a specific implementation, is included in this Recommendation|International Standard as normative Annex A. 1 Scope This Recommendation|International Standard specifies the way in which the underlying service assumed by the protocol defined by ITU
24、-T Rec.X.233|ISO/IEC8473-1 is provided by a subnetwork that provides the OSI Data Link service defined by CCITT Rec. X.212|ISO/IEC8886, through the operation of a Subnetwork Dependent Convergence Function (SNDCF) as described in ISO/IEC8648. This Recommendation|International Standard also provides t
25、he PICS proforma for this protocol, in compliance with the relevant requirements, and in accordance with the relevant guidance, given in CCITTRec. X.290|ISO/IEC9646-1. 2 Normative references The following Recommendations and International Standards contain provisions which, through reference in this
26、 text, constitute provisions of this Recommendation|International Standard. At the time of publication, the editions indicated were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this Recommendation|International Standard are encouraged to invest
27、igate the possibility of applying the most recent editions of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid ITU-T Recomm
28、endations. 2.1 Identical Recommendations|International Standards ITU-T Recommendation X.200 (1994)|ISO/IEC7498-1:1994, Information technology Open Systems Interconnection Basic Reference Model. CCITT Recommendation X.213 (1992)|ISO/IEC 8348:1993, Information technology Network service definition for
29、 Open Systems Interconnection. 2.2 Paired Recommendations|International Standards identical in technical content CCITT Recommendation X.290 (1992), OSI conformance testing methodology and framework for protocol Recommendations for CCITT applications General concepts. ISO/IEC 9646-1:1991, Information
30、 technology Open Systems Interconnection Conformance testing methodology and framework Part1:General concepts. CCITT Recommendation X.212 (1988), Data link service definition for Open Systems Interconnection for CCITT applications. ISO/IEC 8886:1992, Information technology Telecommunications and inf
31、ormation exchange between systems Data link service definition for Open Systems Interconnection. 2.3 Additional references ISO/IEC 8648:1988, Information processing systems Open Systems Interconnection Internal organization of the network layer.ISO/IEC8473-4:1995(E) 2 BSI 10-1999 3 Definitions 3.1 r
32、eference model definitions this Recommendation|International Standard makes use of the following terms defined in ITU-T Rec. X.200|ISO/IEC7498-1: a) network entity; b) Network layer; c) Data link layer; d) service; e) service data unit; f) data link service; g) protocol control information. 3.2 netw
33、ork layer architecture definitions this Recommendation|International Standardmakes use of the following terms definedin ISO/IEC8648: a) subnetwork; b) subnetwork dependent convergence protocol; c) subnetwork dependent convergence function; d) subnetwork access protocol. 3.3 network layer addressing
34、definitions this Recommendation|International Standard makes use of the following term defined in CCITTRec.X.213|ISO/IEC 8348: subnetwork point of attachment. 3.4 data link service definitions this Recommendation|International Standard makes use of the following terms defined in CCITTX.212|ISO/IEC 8
35、886: a) data link service access point address; b) data link connection. 4 Abbreviations CLNP Connectionless-mode network protocol DL Data link layer DLSDU Data link layer service data unit PDU Protocol data unit QOS Quality of service SDU Service data unit SN Subnetwork SNDCF Subnetwork dependent c
36、onvergence function SNDCP Subnetwork dependent convergence protocol SNICP Subnetwork independent convergence protocol SNAcP Subnetwork access protocol SNPA Subnetwork point of attachment SNCR Subnetwork connection reference SNSDU Subnetwork service data unitISO/IEC8473-4:1995(E) BSI 10-1999 3 5 Subn
37、etwork dependent convergence function 5.1 General model The general model for providing the underlying service assumed by the protocol in conjunction with a real subnetwork that uses a connectionless subnetwork access protocol is as follows. The generation of an SN-UNITDATA Request by the CLNP resul
38、ts in the generation of a corresponding subnetwork-specific UNITDATA request by the subnetwork dependent convergence function. The receipt of a subnetwork-specific UNITDATA indication associated with delivery of a connectionless data unit to its destination causes the SNDCF to generate an SN-UNITDAT
39、A Indication to the CLNP. The general model for providing the underlying service assumed by the CLNP in conjunction with a real subnetwork that uses a connection-mode subnetwork access protocol is as follows. The generation of an SN-UNITDATA Request by the CLNP causes a connection (logical channel,
40、logical link, or the equivalent) to be made available for the transmission of SN-User-data. If a connection cannot be made available, the SN-UNITDATA Request is discarded. The receipt of subnetwork-specific PDUs containing SN-User-data causes the SNDCF to generate an SN-UNITDATA Indication to the CL
41、NP. Where a real subnetwork is designed to use either a connectionless-mode or a connection-mode subnetwork access protocol, the provision of the underlying service assumed by the CLNP is achieved by using the connectionless-mode alternative. 5.2 Subnetwork user data The SN-Userdata is an ordered mu
42、ltiple of octets, and is transferred transparently between the specified subnetwork points of attachment. The underlying service assumed by the CLNP is required to support a service data unit size of at least 512 octets. If the minimum service data unit sizes supported by all of the subnetworks invo
43、lved in the transmission of a particular PDU are known to be large enough that segmentation is not required, then either the full protocol or the non-segmenting protocol subset may be used. Data received from a subnetwork with protocol identification specifying this protocol (see ITU-T Rec. X.233|IS
44、O/IEC8473-1) shall be processed according to this Recommendation|International Standard. NOTEData with other protocol identification should be ignored, since it may have been sent by an implementation supporting additional protocols intended for use with this protocol. 5.3 Subnetwork dependent conve
45、rgence functions used with subnetworks that provide the OSIdata link service This subclause defines a mapping of the OSI Data Link service to the underlying service assumed by ITU-T Rec. X.233|ISO/IEC8473-1. The OSI Data Link service definition defines two types of Data Link service: a connectionles
46、s service and a connection-mode service. SNDCFs are defined for subnetworks that provide either of these two modes of service. 5.3.1 SNDCF used with the connectionless Data Link service The primitives defined for provision of the underlying service assumed by the CLNP map directly onto the UNITDATA
47、Request and Indication primitives defined for the connectionless Data Link service. Subnetwork dependent convergence functions perform a mapping of the connectionless Data Link service onto the underlying service assumed by the CLNP. The mapping is as follows. The generation of an SN-UNITDATA reques
48、t by the CLNP results in the generation of a DL-UNITDATA request (as described in CCITT Rec. X.212 | ISO/IEC8886) by the subnetwork dependent convergence function. A corresponding DL-UNITDATA indication prompts the SNDCF to generate an SN-UNITDATA indication to the CLNP. No explicit subnetwork depen
49、dent convergence protocol control information is exchanged between Network entities to provide this mapping of service. The parameters of the SN-UNITDATA primitives are mapped onto the DL-UNITDATA primitives as follows. The SN-Destination-Address and SN-Source-Address parameters are conveyed in the DL-Destination-Address and DL-Source-Address parameters, respectively. The addresses used in the SN-UNITDATA request and indication primitives are the Data Link service access point addresses described in CCITT Rec. X.212|ISO/IEC 88
