ANSI INCITS ISO IEC TR 9575-1995 Information technology - Telecommunications and information exchange between systems - OSI Routeing Framework.pdf

1、 INCITS/ISO/IEC TR 9575:1995 2015 (ISO/IEC TR 9575:1995, IDT) Information technology - Telecommunications and information exchange between systems - OSI Routeing Framework INCITS/ISO/IEC TR 9575:1995 2015 PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensin

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5、tional Standard. Date of Registration: 3/15/2015 Published by American National Standards Institute, 25 West 43rd Street, New York, New York 10036 Copyright 2015 by Information Technology Industry Council (ITI). All rights reserved. These materials are subject to copyright claims of International St

6、andardization Organization (ISO), International Electrotechnical Commission (IEC), American National Standards Institute (ANSI), and Information Technology Industry Council (ITI). Not for resale. No part of this publication may be reproduced in any form, including an electronic retrieval system, wit

7、hout the prior written permission of ITI. All requests pertaining to this standard should be submitted to ITI, 1101 K Street NW, Suite 610, Washington DC 20005. Printed in the United States of America ii ITIC 2015 All rights reserved TECHNICAL REPORT ISOJIEC TR 9575 Second edition 1995-l O-l 5 Infor

8、mation technology - Telecommunications and information exchange between systems - OSI Routeing Framework Technologies de /information - Communication de don - type 2, when the subject is still under technical development or where for any other reason there is the future but not immediate possibility

9、 of an agreement on an International Standard; - type 3, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for example). Technical Reports of types 1 and 2 are subject to review within three years

10、 of publication, to decide whether they can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be reviewed until the data they provide are considered to be no longer valid or useful. ISO/lEC TR 9575, which is a Technical Report of type 3, was prepared

11、 by Joint Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee SC 6, Telecommunications and information exchange between systems. This second edition cancels and replaces the first edition (ISOAEC TR 9575:1990), which has been technically revised. . . . 111 ISO/IEC TR 9575:1995 (E

12、) 0 ISOAEC Introduction In the OS1 environment (OSIE), the possibility exists for any End System (ES) to communicate with any other ES. The physical path (or paths) over which this communication takes place may - include multiple Intermediate Systems (IS); - include multiple subnetwork types; and -

13、traverse multiple, independent organisations. Furthermore, one instance of communications may follow a different path from another instance of communications. Within the Network Layer, the Internal Organisation of the Network Layer (IS0 8648) identifies two functions, Routeing and Relaying, as being

14、 central to the ability for End Systems to communicate through an arbitrary concatenation of subnetworks and Intermediate Systems. Part of the overall function of routeing and relaying is to allow ESs and ISs to find an appropriate path between two or more ESs for a given instance of communications.

15、 Relaying is concerned primarily with the actual transformation and manipulation of Network Protocol Data Units (NPDUs) as they transit Intermediate Systems. Routeing, on the other hand, is primarily concerned with the maintenance and selection of paths through multiple subnetworks and Intermediate

16、Systems which allow NPDUs to flow smoothly between End Systems. There are four important aspects to routeing , i.e.: a) the information required by ESs and ISs (5.1.1) b) the techniques used by ESs and ISs to collect that information (5 .1.2), c) the techniques used by ESs and ISs to distribute that

17、 information (5.1.3), and d) the functions executed by ESs and ISs on that information to determine the paths over which NPDUs flow between pairs of NSAPs (5 .1.4). This Technical Report discusses these aspects of routeing, and describes how various protocols may be employed to effect the OS1 routei

18、ng functions. It does not discuss relaying, except where relaying functions are closely allied with routeing functions. This second edition of ISO/IEC TR 9575 adds the option of interconnecting Routeing Domains using multicast subnetworks, interconnecting Administrative Domains using multicast subne

19、tworks, and providing connectivity within Routeing Domains using multicast subnetworks. TECHNICAL REPORT 0 ISOAEC ISO/IEC TR 9575:1995 (E) Information technology - Telecommunications and information exchange between systems - OS1 Routeing Framework 1 Scope This Technical Report provides a framework

20、in which OS1 protocols for routeing may be developed and to expedite the progression of routeing protocols through the standardisation process. At the time of publication, this report reflected the current state of OS1 Routeing, and does not preclude future extensions and developments. 2 References

21、The following International Standards I ITU-T Recommenda- tions contain provisions which, through reference in this text, constitute provisions of this Technical Report. At the time of publication, the editions indicated were valid. All Standards I Recommendations are subject to revision, and partie

22、s to agree- ments based on this Technical Report are encouraged to inves- tigate the possibility of applying the most recent editions of the Standards I Recommendations listed below. Members of IEC and IS0 maintain registers of currently valid International Stan- dards. The Telecommunication Standar

23、dization Bureau of the ITU maintains a list of currently valid ITU-T Recommenda- tions. 2.1 Identical International Standards I Recommendations - ITU-T Recommendation X.200 (1994) I ISO/IEC 7498- 1: 1994, Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model.

24、 - CCITT Recommendation X.21 3 (1992) I ISO/IEC 8348:1993, Information technology - Open Systems Interconnection - Network service definition. - KU-T Recommendation X.233 (1993) I ISOKEC 8473-l: 1994, Information technology - Protocol for providing the connectionless-mode network service: Protocol s

25、pecification. 2.2 Paired International Standards I Recommendations - ITU-T Recommendation X.223 (1993), Use of X.25 to Provide the OSI Connection-mode Network Service for ITU-T Applications. ISOAEC 8878: 1992, Information technology - Telecommunications and information exchange between systems - Use

26、 of X.25 to provide the OS1 Connection-mode Network Service. 2.3 Additional references - IS0 8648: 1988, Information processing systems - Open Systems Interconnection - Internal organization of the Network Layer. - IS0 9542: 1988, Information processing systems - Telecommunications and information e

27、xchange between systems - End system to intermediate system routeing exchange protocol for use in conjunction with the protocol for providing the connection-less mode network service. - ISO/IEC 10030: 1995, Information technology - Telecommunications and information exchange between systems - End Sy

28、stem Routeing Information Exchange Protocol for use in conjunction with ISO/IEC 8878. ISOAEC 10589:1992, Information technology - Telecommunications and information exchange between systems - Intermediate system to intermediate system intra-domain-routeing routine information exchange protocol for u

29、se in conjunction with the protocol for providing the connectionless-mode Network Service (IS0 8473). ISO/IEC 10747: 1994, Information technology - Telecommunications and information exchange between systems - Protocol for exchange of inter- domain routeing information among intermediate systems to

30、support forwarding of IS0 8473 PDUs. - RFC 1629, Guidelines for OSI NSAP allocation in the Internet. 3 Definitions 3.1 Reference Model Definitions This Technical Report makes use of the following terms defined in ITU-T Rec. X.200 I IS0 7498- 1: a) Network Layer b) Network Service Access Point c) Net

31、work Service Access Point address 9 Network entity e) Routeing 1 ISOAEC TR 9575:1995 (E) 0 ISOAEC f) Network protocol g) Network relay h) Network protocol data unit i) System management j) Layer management 3.2 Network Layer Architecture Definitions This Technical Report makes use of the following te

32、rms defined in IS0 8648: a) Subnetwork b) End system c) Intermediate system 9 Subnetwork service 3.3 Network Layer Addressing Definitions This Technical Report makes use of the following terms defined in CCITT Rec. X.21 3 I ISO/IEC 8348. a) Subnetwork address b) Subnetwork Point of Attachment 3.4 Ro

33、uteing Framework Definitions For the purpose of this Technical Report the following definitions apply. 3.4.1 Administrative Domain: A collection of End systems, Intermediate systems, and subnetworks operated by a single organisation or administrative authority. The components which make up the domai

34、n are assumed to interoperate with a significant degree of mutual trust among themselves, but interoperate with other Administrative Domains in a mutually suspicious manner. NOTE: The term Administrative Domnirz is not intended to have any particular relationship to an Adrninisrafion as defined by t

35、he ITU-T. A ITU Administration may in fact operate an Administrative Domain, but this would be no different from an Administrative Domain operated by any organisation from the point of view of this Routeing Framework. 3.4.2 Routeing Domain: A set of End Systems and Intermediate Systems which operate

36、 according to the same routeing procedures and which is wholly contained within a single Administrative Domain. See 8.1.2.1 for a precise formal definition of this concept. 3.4.3 common domain: An Administrative Domain which is not a member of a higher level domain. A common domain is the highest le

37、vel in the routeing hierarchy. There is no single domain above the common domain. In this sense, the routeing hierarchy is in fact multiple hierarchies, with the common domain as the highest element of each hierarchy. Where there are multiple common domains, they co-operate as peers to make it possi

38、ble to route to any NSAP in the OSIE. 3.4.4 hop: The traversal of a single subnetwork by a PDU. 3.4.5 black hole: A situation in which an Intermediate System, due to a breakdown of the routeing procedures, malicious intent, or lack of information, discards or otherwise refuses to forward all traffic

39、 directed to it. A black hole may also be formed on a connectionless subnetwork when the intended recipient of traffic is unavailable. 3.4.6 Subnetwork Address Resolution Entity: A network layer entity available on a subnetwork which acts as a repository for, and source of, routeing information for

40、that subnetwork. 3.4.7 multicast subnetwork: a subnetwork in which a single data unit transmitted by a source is received by multiple destinations. 3.4.8 multicast communication: the use of a multicast subnetwork for data transmission. 4 Symbols and Abbreviations BIS ES IS LAN NPDU NSAP OSIE PDU QoS

41、 SN SNARE SNPA WAN Border Intermediate System End System Intermediate System Local Area Network Network Protocol Data Unit Network Service Access Point Open System Interconnection Environment Protocol Data Unit Quality of Service Subnetwork Subnetwork Address Resolution Entity Subnetwork Point of At

42、tachment Wide Area Network 5 Routeing Concepts 5.1 Functional Decomposition of Routeing OS1 Routeing can be decomposed into four different but interrelated aspects. The purposes of this division are to: - conceptually clarify the functions of routeing; 2 0 ISO/IEC ISO/IEC TR 9575:1995 (E) - simplify

43、 the design of routeing protocols by breaking routeing into its component parts; and - make the routeing functions as flexible as is practical by allowing for degrees of freedom in each aspect. The four aspects are described in the following clauses. Figure 1 below illustrates the relationship among

44、 these four aspects of routeing. 5.1.1 Routeing Information Base The Routeing Information Base comprises the complete information required by a particular ES or IS to accomplish routeing. Such information might include: - Next hop routeing tables. These are tables which relate destination NSAPs to t

45、he potential next subnetwork hops (e.g. local and remote SNPAs) which might be used to forward the PDU closer to its destination. - Lists of neighbour ESs and ISs. These lists enable an ES or IS to ascertain the local topology. - Measured QoS characteristics of a datalink or subnetwork path. These m

46、easurements allow the routeing functions to adapt to QoS changes. - Network maps. These are complete topological graphs of a portion of the global network. Such maps can be used to compute shortest paths to destination NSAPs using any of a number of routeing metrics. 5.1.2 Information Collection ESs

47、 and ISs build up their routeing information bases by collecting information from their local environment and from other systems. Some example sources of information are: measurement protocols, policy input from System Management, directory lookup functions, and routeing protocols. The information c

48、ollection function is illustrated in figure 1 by the box labelled Update Receive. 5.1.3 Information Distribution Systems may inform other systems of pertinent information in their local routeing information base by distributing this information. Some examples of information distribution techniques i

49、nclude: routeing protocols and interactions through the management information bases. The information distribution function is illustrated in figure 1 by the box labelled Update Send. Update Send Routeing Information Base Forwarding Information Base Forward Figure 1 - Decomposition of the Routeing Function ISOAEC TR 9575:1995 (E) 0 ISOAEC 5.1.4 Route Calculation and Maintenance These are the internal functions executed