ISO/IEC INTERNATIONAL STANDARD 7498-1 Second edition 1994-11-15 Correctedand reprinted 1996-06-15 Information technology Open Systems Interconnection -- Basic Reference Model: The Basic Model Technologies de I'information -Modele de référence de base pour Iinterconnexion de systemes ouverts (Osl): Le modele debase IEC so Reference number ISO/IEC 7498-1:1994(E) Copyright Intermational Organization for Standardization rovided by IHS cense with rmitted without license from IHS Not for Resale ISO/IEC 7498-1:1994(E) Contents Page 1 Scope 1 2 Definitions 2 3 2 Notation.. 4 Introduction to Open Systems Interconnection (OSI) 2 4.1 Definitions.. 2 4.2 Open System Interconnection Environment 3 4.3 Modelling the OSI Environment.. 4 5 Concepts of a layered architecture . 5 5.1 Introduction.. 5 5.2 Principles of layering .. 6 5.3 Communication between peer-entities. 9 5.4 Identifiers. 13 5.5 Properties of service-access-points 14 5.6 Data-units. 15 5.7 The nature of the (N)-service 16 5.8 Elements of layer operation . 16 5.9 27 Routing...... 5.10 Quality Of Service (QOS).. 27 6 Introduction to the specific OSI layers 28 6.1 Specific layers. 28 6.2 The principles used to determine the seven layers in the Reference Model . 29 6.3 Layer descriptions........ 30 6.4 Combinations of connection-mode and connectioniess-mode... 30 6.5 Configurations of OsI Open Systems... 31 Detailed description of the resulting OSI architecture 32 7.1 Application Layer 32 7.2 Presentation Layer 33 7.3 Session Layer 34 7.4 Transport Layer 37 7.5 Network Layer 41 7.6 Data Link Layer 46 7.7 Physical Layer 49 ISO/IEC1994 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, inciuding photocopying and microfilm, without permission in writing from the publisher. ISO/IEC Copyright Office ·Case postale 56 · CH-1211 Geneve 20 · Switzerland Printed in Switzerland ii Copyright Intermational Organization for Standardization nse from IHS Not for Resale ISO/IEC 7498-1:1994(E) @ ISO/IEC 8 Management aspects of OSI. 52 8.1 Definitions... 52 8.2 Introduction... 53 8.3 53 8.4 Principles for positioning management functions... 54 9 Compliance and Consistency with this reference model... 54 9.1 Definitions.... 54 9.2 Application of consistency and compliance requirements 55 Annex A-I Brief explanation of how the layers were chosen .... 56 Annex B -- Alphabetical index to definitions .. 57 iii Copyright Intermational Organization for Standardization ited without license from IHS Not for Resale ISO/IEC 7498-1:1994(E) @ ISO/IEC Foreword ISO (the International Organization for Standardization) and IEC (the Inter- nationalElectrotechnicalCommission)formthespecializedsystemforworldwide 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 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 technology, ISO and IEC have established a joint technical committee, ISO/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 Joint Technical Committee ISO/IEC JTC 1, Information technology, 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 (ISO 7498:1984), which has been technically revised. ISO/IEC 7498 consists of the following parts, under the general titl