1、BRITISH STANDARD BS ISO/IEC TR10172:1991 Implementation of ISO/IEC TR10172:1991 Information technology Telecommunications and information exchange between systems Network/Transport Protocol interworking specificationBSISO/IECTR10172:1991 This BritishStandard, having been prepared under the direction
2、of the Information Systems Technology Standards Policy Committee, was published under the authority of the Standards Board and comes intoeffect on 29November1991 BSI 02-2000 The following BSI references relate to the work on this standard: Committee reference IST/6 Draft for comment91/67305 DC ISBN
3、0 580 20355 7 Committees responsible for this BritishStandard The preparation of this BritishStandard was entrusted by the Information Systems Technology Standards Policy Committee (IST/-) to Technical Committee IST/6, upon which the following bodies were represented: British Computer Society Depart
4、ment of Trade and Industry (National Physical Laboratory) EEA (The Association of Electronics, Telecommunications and Business Equipment Industries) Electricity Industry in UnitedKingdom HM Treasury (Central Computer and Telecommunications Agency) Joint Network Team National Health Services Amendmen
5、ts issued since publication Amd. No. Date CommentsBSISO/IECTR10172:1991 BSI 02-2000 i Contents Page Committees responsible Inside front cover National foreword ii Foreword iii Text of ISO/IEC TR10172 1BSISO/IECTR10172:1991 ii BSI 02-2000 National foreword This BritishStandard reproduces verbatim ISO
6、/IEC TR10172:1991 and implements it as the UK national standard. This BritishStandard 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 resp
7、onsible international 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
8、 BSI Sales Department, 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
9、 from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, theISO/IEC TR title page, pagesii toiv, pages1 to18 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indic
10、ated in the amendment table on the inside front cover.ISO/IECTR10172:1991(E) ii BSI 02-2000 Contents Page Foreword iii Introduction 1 1 Scope 1 2 Normative references 1 3 Definitions 2 4 Symbols and abbreviations 3 5 Overview of IFU 3 6 Conformance 6 7 Environmental requirements for use of an IFU 6
11、8 Operation of the Active Transport Layer Relay 7 9 Operation of the Passive Transport Layer Relay 11 10 Selection of IFU mode of operation 13 Annex A (normative) PICS proforma 16 Annex B (informative) Local coordination between TCs in an ATLR 18 Figure 1 An active Transport Relay in an example conf
12、iguration 4 Figure 2 A passive Transport Relay in an example configuration 4ISO/IECTR10172:1991(E) BSI 02-2000 iii Foreword ISO (the International Organization for Standardization) and IEC (theInternational Electrotechnical Commission) form the specialized system forworldwide standardization. Nation
13、al bodies that are members of ISO or IECparticipate 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 collaborate in fields of mutual interest. O
14、ther international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take partin the work. In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC1. The main task of technical committees is to prepare Internation
15、al Standards, but in exceptional circumstances a technical committee may propose the publication of a Technical Report of one of the following types: type1, when the required support cannot be obtained for the publication of an International Standard, despite repeated efforts; type2, when the subjec
16、t is still under technical development or where for any other reason there is the future but not immediate possibility of an agreement on an International Standard; type3, when a technical committee has collected data of a different kind from that which is normally published as an International Stan
17、dard (“state of the art”, for example). Technical Reports of types1 and2 are subject to review within three years of publication, to decide whether they can be transformed into International Standards. Technical Reports of type3 do not necessarily have to be reviewed until the data they provide are
18、considered to be no longer valid or useful. ISO/IEC/TR10172, which is a Technical Report of type2, was prepared by Joint Technical Committee ISO/IEC JTC1, Information technology. Annex A forms an integral part of this Technical Report. Annex B is for information only.iv blankISO/IECTR10172:1991(E) B
19、SI 02-2000 1 Introduction There exist today two different types of data communications network layer protocols under the auspices of ISO Open Systems Interconnection (OSI), yet systems operating either of these protocol types cannot interconnect. The Connection-mode Network Protocol (CONP) ISO8208/(
20、X.25) operated in accordance with ISO8878 cannot interwork with the Connectionless-mode Network Protocol (CLNP) ISO8473. In order to achieve interworking of these two disparate protocols there is need for a mediating device to perform relaying and/or conversion of PDUs from one network protocol type
21、 to another, this device is termed an Interworking Functional Unit (IFU). In solving this problem of CO/CL Interworking two broad objectives must be considered: a) the IFU must not impose any changes on existing end-systems or recognized standards, its operation must be transparent to end-systems; a
22、nd b) it must provide interconnection to the widest user community within its scope of operation. This Technical Report identifies a CO/CL interworking solution which is based on three modes of operation: a network layer relay mode (NLR), a passive transport layer relay (PTLR) mode, and an active tr
23、ansport layer relay (ATLR) mode. Some of these modes of operation lie within the OSIarchitecture, others lie outside the scope of the OSI architecture. For this reason an International Standard is inappropriate and this form of publication has been chosen. It is the express intention of the ISO/IEC
24、Subcommittee responsible for this Technical Report (ISO/IEC JTC1/SC6) that the form of publication shall be, and shall remain, a Technical Report. It is the clear intention of SC6 that the content of this Technical Report is not appropriate for conversion into an International Standard. 1 Scope This
25、 Technical Report a) Specifies the circumstances in which Interworking Functional Units may be used to provide the OSI Connection-mode Transport Service end-to-end between two end systems, where one of the end systems is accessed using the connection-mode transport protocol as defined in ISO8073/Add
26、.2 1)in combination with the protocol defined in ISO8473; the other end system is accessed using the connection-mode transport protocol as defined in ISO8073 in combination with the procedures defined in ISO8208/ISO8878 2) . b) Specifies various sets of procedures for the operation of such Interwork
27、ing Functional Units. c) Specifies how IFUs which operate more than one of these sets of procedures may choose which set to use in a given instance, taking into account the possibility that some end systems may operate both types of Network Service. d) Specifies the requirements for IFUs to operate
28、in series and/or in parallel. NOTEOnly the Network Layer Relay (NLR) mode of operation is within the scope of OSI. The Active Transport Layer Relay (ATLR) and Passive Transport Layer Relay (PTLR) modes of operation are not considered to be OSI operations because ISO7498 does not define relaying to b
29、e a Transport Layer function. The field of application also covers the case where the two end systems operate the same Network Layer protocol but are interconnected via IFUs employing ATLR or PTLR operation. 2 Normative references The following standards contain provisions which, through reference i
30、n this text, constitute provisions of this Technical Report. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Technical Report are encouraged to investigate the possibility of applying the most recent editio
31、ns of the standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO7498:1984, Information processing systems Open Systems Interconnection Basic Reference Model. 1) For purposes of conciseness and distinction, when ISO8073/Add.2 is used througho
32、ut this Technical Report it shall be taken to mean ISO8073 as modified by ISO8073/Add.2, i.e.“use of Transport Class Four Operation over Connectionless Network Service”. 2) For purposes of conciseness ISO8208/ISO8878 shall be taken to mean ISO8208 operated in accordance with ISO8878.ISO/IECTR10172:1
33、991(E) 2 BSI 02-2000 ISO7498-3:1986, Information processing systems Open Systems Interconnection Basic Reference Model Part3: Naming and Addressing. ISO8072:1986, Information processing systems Open Systems Interconnection Transport Service Definition. ISO8073:1988, Information processing systems Op
34、en Systems Interconnection Connection oriented transport protocol specification. ISO8073/Add.1:1988, Information processing systems Open Systems Interconnection Connection oriented transport protocol specification Addendum1: Network connection management subprotocol. ISO8073/Add.2:1989, Information
35、processing systems Open Systems Interconnection Connection oriented transport protocol specification Addendum2: Class four operation over connectionless network service. ISO/IEC8208:1990, Information processing systems Data communications X.25 Packet Layer Protocol for Data Terminal Equipment. ISO83
36、48/Add.2:1988, Information processing systems Data communications Network Service definition Addendum2: Network Layer addressing. ISO8473:1988, Information processing systems Data communications Protocol for providing the connectionless-mode network service. ISO8648:1988, Information processing syst
37、ems Open Systems Interconnection Internal Organization of the Network layer. ISO8878:1987, Information processing systems Data communications Use of X.25 to provide the OSI connection-mode network service. ISO/IEC8881:1989, Information processing systems Data communications Use of X.25 packet level
38、protocol in local area network. ISO9542:1988, Information processing systems Telecommunications and information exchange between systems End system to Intermediate system routeing exchange protocol for use in conjunction with the Protocol for providing the connectionless-mode network service (ISO847
39、3). ISO/IEC9574:1989, Information technology Telecommunications and information exchange between systems Provision of the OSI connection-mode network service by packet mode terminal equipment connected to an Integrated Services Digital Network (ISDN). ISO/IEC TR9577:1990, Information technology Tele
40、communications and information exchange between systems Protocol Identification in the network layer. ISO/IEC10028:, Information processing systemsData Communications Definition of the relaying functions of a Network Layer intermediate system 3) . ISO/IEC TR10029:1989, Information technology Telecom
41、munications and information exchange between systems Operation of an X.25 interworking unit. ISO/IEC10177:, Information technology Telecommunications and Information Exchange between Systems Intermediate system support of the OSI connection-mode Network Service using ISO8208 in accordance with ISO/I
42、EC10028 3) . 3 Definitions 3.1 Reference Model definitions This Technical Report makes use of the following concepts defined in ISO7498: 3.1.1 (N)-layer 3.1.2 (N)-service access point 3.1.3 (N)-address 3.1.4 Routeing 3.1.5 (N)-relay 3.1.6 (N)-protocol data unit 3.1.7 Title 3.1.8 (N)-interface-data-u
43、nit 3.2 Network Layer Architecture definitions This Technical Report makes use of the following concepts from ISO8648: 3.2.1 Intermediate system 3.2.2 Subnetwork independent convergence protocol 3.3 Additional definitions For the purposes of this Technical Report, the following definitions apply: 3.
44、3.1 end system a system in which there is a transport entity providing service to a session entity in an instance of communication NOTEThe term end system in ISO7498 is interpreted to mean a system in which there is a transport entity in an instance of communication. Since ISO7498 does not permit re
45、laying above the Network layer, this is equivalent to the definition given above. However, this Technical Report discusses relaying at the transport layer; consequently the definition given above is used in order to distinguish end systems from systems relaying at the transport layer. 3) To be publi
46、shed.ISO/IECTR10172:1991(E) BSI 02-2000 3 3.3.2 (N)-SAP Address: (N)-Address NOTEThe terms (N)-SAP Address and (N)-Address are used synonymously, as in most Network and Transport layer standards. 4 Symbols and abbreviations 5 Overview of IFU 5.1 Applicability of IFU An IFU is applicable only in cert
47、ain restricted circumstances where CO/CL interworking is necessary to achieve interconnection of two otherwise incompatible end systems. Any other use of an IFU is outside the scope of this Technical Report. The restricted circumstances for requirement of an IFU are specified in clause7. 5.2 IFU mod
48、es of operation Three modes of operation are identified by means of which an IFU may provide an end-to-end transport service a) Active Transport Layer Relay (ATLR) This mode of IFU operation, illustrated in Figure 1, provides an end-to-end transport service by operating a separate Transport Connecti
49、on to each of the connected systems (endsystems or other IFUs) and relaying data from one connection to the other. The two connections can be independent, using different transport protocol classes and parameters. The IFU will preserve the end-to-end transmission of TSDUs, thus in effect providing a single Transport Connection between the two end systems. The IFU does not necessarily preserve the distribution of data between TPDUs, although it may choose to do so, forexample to optimise performance, in cases where
