1、I N T E R N AT I 0 N A L STANDARD ISO/IEC 7498-1 Second edition 1994-1 1-1 5 (Reaffirmed 2004) Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model Technologies de Iinforrnation - Modeie de rgference de base pour iinterconnexion de systemes ouverts (OSI): Le
2、 modele de base National Standard of Canada CA N/CSA-ISO/IEC-7498-1-95 International Standard ISO/IEC 7498-1 : 1994 has been adopted, without modification, as CAN/CSA-ISO/IEC-7498-1-95, which has been approved as a National Standard of Canada by the Standards Council of Canada. May 1995 Reference nu
3、mber ISO/IEC 7498-1 :1994(E) ISOflEC 7498-1:1994(E) Contents 1 Scope 2 Definitions 3 Notation 4 Introduction to Open Systems Interconnection (OX) 4.1 Definitions . 4.2 Open System Interconnection Environment . 4.3 Modelling the OS1 Environment . 5.1 Introduction . 5.2 Principles of layering 5.3 Comm
4、unication between peer-entities 5.4 Identifiers 5.5 Properties of service-access-points . 5.6 Data-units 5.7 The nature of the (N)-service 5.8 Elements of layer operation 5.10 Quality Of Service (QOS) . 5 Concepts of a layered architecture . 5.9 Routing 6 7 Introduction to the specific OS1 Iayers .
5、6.2 The principles used to determine the seven layers in the Reference Model . 6.4 Combinations of connection-mode and connectionless-mode 6.5 Configurations of OS1 Open Systems . Detailed description of the resulting OS1 architecture . 6.1 Specific layers . 6.3 Layer descriptions . 7.1 Application
6、Layer . 7.2 Presentation Layer 7.3 Session Layer 7.4 Transport Layer . 7.5 Network Layer 7.6 Data Link Layer 7.7 Physical Layer . Page i 2 2 2 2 3 4 5 5 6 9 13 14 15 16 16 27 27 28 28 29 30 30 31 32 32 33 34 37 41 46 49 0 ISOlIEC 1994 All rights reserved . Unless otherwise specified. no part of this
7、 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 . ISOlIEC Copyright Office Case postale 56 CH-1211 Gedve 20 Switzerland Printed in Switzerland 11 0 ISOAEC ISO/IEC
8、7498-1:1994(E) 8 Management aspects of OS1 . 52 8.1 Definitions . 52 8.2 Introduction . 53 8.3 Categories of management activities 53 9 CompIiance and Consistency with this reference model 54 9.1 Definitions . 54 56 57 8.4 Principles for positioning management functions . 54 9.2 Application of consi
9、stency and compliance requirements 55 Annex A - Brief explanation of how the layers were chosen Annex B - Alphabetical index to definitions . . 111 ISO/IEC 7498-1: 1994(E) 0 ISOIIEC Foreword IS0 (the International Organization for Standardization) and IEC (the Inter- national Electrotechnical Commis
10、sion) form the specialized system for worldwide standardization. National bodies that are members of IS0 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. IS0
11、and IEC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, 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/
12、IEC JTC 1. 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 least 75 % of the national bodies casting a vote. International Standard ISO/IEC 7498- 1 was prepared by Jo
13、int Technical Committee ISOAEC JTC I, Information technolugy, in collaboration with ITU-T. The identical text is published as ITU-T Recommendation X.200. This second edition, along with parts 2, 3 and 4, cancels and replaces the first edition (IS0 7498: 1984), which has been technically revised. ISO
14、/IEC 7498 consists of the following parts, under the general title Information technology - open Systems Interconnection - Basic Reference Model: - Part I: The Basic Model - Part 2: Security Architecture - Part 3: Naming and addressing - Part 4: Management framework iv ISO/IEC 7498-1 :1994(E) Introd
15、uction This reference model provides a common basis for the coordination of standards development for the purpose of systems interconnection, while allowing existing standards to be placed into perspective within the overall reference model. It also identifies areas for developing and improving stan
16、dards and provides a common reference for maintaming consistency among all related standards. The text was developed jointly with ITU-T and the main intent of this revision is to introduce the joint text, which incorporates inclusion of the concept of connectionless transmission, in addition to a nu
17、mber of technical and editorial refinements. V ISODEC 7498-1 : 1994(E) INTERNATIONAL STANDARD CCITT FtECOMMENDATION INFORMATION TECHNOLOGY - OPEN SYSTEMS INTERCONNECTION - BASIC REFERENCE MODEL: THJ3 BASIC MODEL Scope 1.1 The purpose of this Reference Model of Open Systems Interconnection is to prov
18、ide a common basis for the coordination of standards development for the purpose of systems interconnection, while allowing existing standards to be placed into perspective within the overall Reference Model. 1.2 systems that are “open” to one another for this purpose by virtue of their mutual use o
19、f the applicable standards. The term Open Systems Interconnection (OSI) qualifies standards for the exchange of information among 1.3 interconnection, but refers to the mutual recognition and support of the applicable standards. The fact that a system is open does not imply any pxticular systems imp
20、lementation, technology or means of 1.4 It is also the purpose of this Reference Model to identify areas for developing or improving standards, and to provide a common reference for maintaining consistency of all related standards, It is not the intent of this Reference Model either to serve as an i
21、mplementation specification, or to be a basis for appraising the conformance of actual implementations, or to provide a sufficient level of detail to define precisely the services and protocols of the interconnection architecture. Rather, this Reference Model provides a conceptual and functional fra
22、mework which allows international teams of experts to work productively and independently on the development of standards for each layer of the Reference Model for OSI. 1.5 demands. This flexibility is also intended to allow the phased transition from existing implementations to OS1 standards. The R
23、eference Model has sufficient flexibility to accommodate advances in technology and expansion in user 1.6 While the scope of the general architectural principles required for OS1 is very broad, this Reference Model is primarily concerned with systems comprising terminals, computers, and associated d
24、evices and the means for transferring information between such systems. Other aspects of OS1 requiring attention are described briefly (see 4.2). 1.7 The description of the Basic Reference Model of OS1 is developed in stages: 1.8 of the interconnection, and describes the modelling principles used in
25、 OSI. Clause 4 establishes the reasons for Open Systems Interconnection, defines what is being connected, the scope 1.9 what layering means, and the principles used to describe layers. Clause 5 describes the general nature of the architecture of the Reference Model; namely that it is layered, 1.10 1
26、.11 1.12 1.13 1.14 Clause 6 names, and introduces the specific layers of the architecture. Clause 7 provides the description of the specific layers. Clause 8 provides the description of Management Aspects of OSI. Clause 9 specifies compliance and consistency with the OS1 Reference Model. An indicati
27、on of how the layers were chosen is given in Annex A to this Basic Reference Model. 1.15 Additional aspects of this Reference Model beyond the basic aspects are described in several parts. The first part describes the Basic Reference Model. The second part describes the architecture for OS1 Security
28、. The third part describes OS1 Naming and Addressing. The fourth describes OS1 System Management. 1.16 the boundaries estabhshed by the Reference Model. The Basic Reference Model serves as a framework for the definition of services and protocols which fit within 1.17 In those few cases where a featu
29、re is explicitly marked (optional) in the Basic Reference Model it should remain optional in the corresponding service or protocol (even if at a given instant the two cases of the option are not yet documented). ITU-T Rec. X.200 (1994 E) 1 ISO/IEC 7498-1 : 1994(E) 1.18 specification for systems, nor
30、 a basis for appraising the conformance of impIernentations. 1.19 functions, to facilitate implementation and compatibility. This Reference Model does not specify services and protocols for OSI. It is neither an implementation For standards which meet the OS1 requirements, a small number of practica
31、l subsets are defined from optional 2 Definitions Definitions of terms are included at the beginning of individual clauses and sub-clauses. An index of these terms is provided in Annex B for easy reference. 3 Notation 3.1 layers: Layers are introduced in clause 5. An (N)-, (N+l)- and (N-1)- notation
32、 is used to identify and relate adjacent (N)-layer: any specific layer; (Ni-1)-layer: the next higher layer; (N-1)-layer: the next lower layer. This notation is also used for other concepts in the model which are related to these layers, for example (N)-protocol, (N+I)-service. 3.2 Clause 6 introduc
33、es names for individual layers. When referring to these layers by name, the (N)-, (N+1)- and (N-1)- prefixes are replaced by the names of the layers, for example transport-protocol, session-entity, and network-service. 4 Introduction to Open Systems Interconnection (ON) NOTE - The general principles
34、 described in clauses 4 and 5 hold for all layers of the Reference Model, unless layer specific statements to the contrary are made in clauses 6 and 7. 4.1 Definitions 4.1.1 real system: A set of one or more computers, the associated software, peripherals, terminals, human operators, physical proces
35、ses, information transfer means, etc., that forms an autonomous whole capable of performing information processing andor information transfer. 4.1.2 communication with other real systems. real open system: A real system which complies with the requirements of OS1 standards in its 4.1.3 pertinent to
36、OSI. open system: The representation within the Reference Model of those aspects of a real open system that are 4.1.4 particular application. application process: An element within a real open system which performs the information processing for a 4.1.5 Open System Interconnection Environment (OSTE:
37、 An abstract representation of the set of concepts, elements, functions, services, protocols, etc., as defined by the OS1 Reference Model and the derived specific standards which, when applied, enable communications among open systems. 4.1.6 pertinent to OSI. Local System Environment (LSE): An abstr
38、act representation of that part of the real system that is not NOTE -The LSE may include functions necessary for non-OS1 communication. 4.1.7 process in support of a specific occasion of information processing. application-process-invocation: A specific utilization of part or all of the capabilities
39、 of a given application 4.1.8 processing capabilities. application-process-type: A description of a class of application processes in terms of a set of information 2 ITU-T Rec. X.200 (1994 E) ISODEC 7498-1 : 1994(E) 4.2 Open System Interconnection Environment 4.2.1 In the concept of OSI, a real syst
40、em is a set of one or more computers, associated software, peripherals, terminals, human operators, physical processes, information transfer means, etc., that forms an autonomous whole capable of performing infomation processing andor information transfer. 4.2.2 a particular application. An applicat
41、ion process is an element within a real open system which performs the information processing for 3.2.3 4.2.4 Application processes can represent manual processes, computerized processes or physical processes. Some examples of application processes that are applicable to this open system definition
42、are the following: a) a person operating a banking terminal is a manual application-process; b) a FORTRAN program executing in a computer center and accessing a remote database is a computerized application-process; the remote database management systems server is also an application-process; and c)
43、 a process control program executing in a dedicated computer attached to some industrial equipment and linked into a plant control system is a physical application-process. 4.2.5 An application process represents a set of resources, including processing resources, within a real open system that may
44、be used to perform a particular information processing activity. An application process may organize its interactions with other application processes in whatever way is necessary to achieve a particular infomation processing goal: no constraints are imposed by this Reference Model either on the for
45、m of these interactions or on the possible relationships that may exist between them. 4.2.6 The activity of a given application process is represented by one or more application process invocations. Cooperation between application processes takes place via relationships established among application
46、 process invocations. At a particular time, an application process may be represented by none, one or more application process invocations. An application process invocation is responsible for coordinating its interactions with other application process invocations. Such coordination is outside the
47、scope of this Reference Model. 4.2.7 each individual real open system). OS1 is concerned with the exchange of information between open systems (and not the internal functioning of 4.2.8 transfer of information between open systems. As shown in Figure 1, the physical media for Open Systems Interconne
48、ction provides the means for the Physical media Figure 1 - Open systems connected by physical media 4.2.9 to interconnection are outside the scope of OSL OS1 is concerned only with the interconnection of systems. A11 other aspects of systems which are not related ITU-T Rec. X.200 (1994 E) 3 ISO/IEC
49、7498-1 ; 1994(E) 4.2.10 OS1 is concerned not only with the transfer of information between systems, i.e. transmission, but also with their capability to interwork to achieve a common (distributed) task. Tn other words, OSI is concerned with the interconnection aspects of cooperation1) between systems, which is implied by the expression “systems interconnection.” 4.2.11 The objective of OS1 is to define a set of standards to enable re
