ISO/IEC INTERNATIONAL STANDARD 8208 Fourth edition 2000-11-01 Information technology Data communications X.25 Packet Layer Protocol for Data Terminal Equipment Technologies de I'information Communication de données Protocole X.25 de couche paquet pour terminal de donnees Reference number ISO/IEC 8208:2000(E) E( @ISO/IEC 2000 Copyright International Organization for Standardization itted without license from IHS Not for Resale ISO/IEC 8208:2000(E) PDFdisclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this area Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event ISO/IEC2000 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, including photocopying and microfilm, without permission in writing from either isO at the address below or isO's member body in the country of the requester. ISO copyright office Case postale 56.CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail [email protected] Web www.iso.ch Printed in Switzerland @ISO/IEC2000-Allrightsreserved or networking permitted without license from IHS Not for Resale ISO/IEC 8208 : 2000(E) CONTENTS Page Foreword 1 Scope.. 2.1Identical Recommendations IInternational Standards 2.2 Paired Recommendations I International Standards equivalent in technical content. 3 General considerations .... 3.1 Compatibility with versions of Recommendation X.25 3.2Environments... 3.3 Differences in DTE/DTE and DTE/DCE operation 3.4 Operation over circuit-switched connections. 3.5 Provision of the OSI Network Service. 3.6 External Packet Layer interactions. 3.7 Logical channels 3.8 Packet Layer entity 3.9Packet types 3.10 Procedures for initialization. 4 Procedures for restart. 4.1 Originating a restart request 10 4.2 Receiving a restart indication. 4.3 Restart collision . 12 4.4Restartconfirmation. 12 4.5 Determining“DTE" or “DCE" characteristics 5 Procedures for Virtual Call setup and clearing .13 5.1Ready state. 13 5.2 Procedures for Virtual Call setup 13 5.3 Rejecting a call... 15 5.4 Aborting a call request... 15 5.5 Procedures for Virtual Call clearing 15 6Procedures for data and interrupt transfer. ..16 6.1 States for data and interrupt transfer........ 17 6.2MaximumUserDataFieldlengthofDATApackets 6.3Delivery Confirmation bit.. 6.4 More Data mark..... 6.5Completepacket sequence 6..6 Qualifier bit...... 6.7 Fragmentation and reassembly of messages. 19 6..8 Procedures for interrupt .... 6.9Transit delayof DATApackets 21 7 Procedures for flow control.. 21 7.1 Flow control.... 7.2 Throughput characteristics and throughput classes ISO/IEC 2000 - All rights reserved ii Copyright International Organization for Standardization Not for Resale ISO/IEC 8208 : 2000(E) 5 8.1 Originating a reset request .. .27 8.2 Receiving a reset indication . 27 8.3 Reset collision.... 8.4Reset confirmation... .27 9 Effects of clear, reset, and restart procedures on the transfer of packets ... 10 Effects of Layers 1 and 2 on the Packet Layer.. 28 11 Error handling. .28 11.1 The DIAGNOSTIC packet.. 29 11.2 Nonreceipt of window-rotation information . 29 11.3 Receipt of erroneous DATA packets .. .30 12 Packet formats.. 12.1 General.... 12.2 Call setup and call clearing packets ....33 12.3 DATA and interrupt packets .. 12.4 Flow control packets... ..44 12.5 Reset packets... 12.6 Restart packets. ..47 12.7 DIAGNOSTIC packet ..48 12.8REJECTpacket. ..49 12.9Registration packets ..50 13