ISO/IEC INTERNATIONAL STANDARD 8480 Second edition 1995-09-15 Information technology Telecommunications and information exchange between systems DTE/DCE interface back-up control operation using ITU-T Recommendation V.24 interchange circuits Technologies de I'information - Télecommunications et échange d'information entre systemes -Dispositif de secours a la jonction ETTD/ETCD realisé a I'aide des circuits d'échange de la Recommandation UIT-T V.24 IEC Reference number ISO/IEC8480:1995(E) Copyright Intemational Organization for Standardization No repr Not for Resale ISO/IEC8480:1995(E) Foreword national Electrotechnical Commission) form the specialized system for worldwide standardization. National bodies that are members of iso or IEC participate in the development of International Standards through with particular fields of technical activity. ISO and IEc technical commit- tees collaborate in fields of mutual interest. Other international organiza- tions, 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 vot- ing. Publication as an International Standard requires approval by at least 75%ofthenationalbodiescastingavote. International Standard ISO/IEC 8480 wasprepared byJointTechnical Committee ISO/lEC JTC 1, Information technology, Subcommittee SC 6, Telecommunications and information exchange between systems. Thissecond editioncancelsandreplacesthe firstedition (Is0 8480:1987),which has been technically revised. O. ISO/IEC 1995 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 the publisher. ISO/IEC Copyright Office · Case Postale 56 · CH-1211 Geneve 20 · Switzerland Printed in Switzerland ii CopyrightIntemationalOrganizationforStandardization No reproduct d without license from IHS Not for Resale @ISO/EC ISO/IEC 8480: 1995 (E) Introduction Where data transmission is provided on a leased line, there may be a whenever transmission via the leased line is, for any reason, not possible. There are several possible back-up facilities: back-up of a 2-wire leased line by one GsTN line; - back-upof a 4-wire leased line byone GsTN line; back-up of a 4-wire leased line by two GsTN lines; back-up of a 2-wire/4-wire leased line by one/two lines of a private switched network; back-up of a 2-wire leased line by one IsDN line, using a terminal adaptor'; back-up of a 4-wire leased line by one isDN line, using a terminal adaptor' NOTES 1 - This list may not be exhaustive. 2 - the terminai adaptor may be separate equipment or physically combined withtheDCE The variety of facilities should not be visible in the protocol used at the DTE/DCE interface to exchange the interface control and status information necessary for back-up control. To achieve this, a standardised approach to the required protocoi is essential.The majorityofapplicationsare,however,restrictedtothefirsttwoofthe listedpossibilities. In consequence, this International Standard describes the protocol requirements where only one back-up facility is provided as the alternative to data transmission on the leased line. For other arrangements of facilities, although this International Standard is not directly applicable, it nevertheless should be used as a guide to the protocol requirements. Terminal Adaptor functions are described in ITU-T Recommendation (previously CCITT Recommendation)V.110, Support of data terminal network, and CCITT Recommendation V.120, Support by an ISDN of data terminal equipment with V-series type interfaces with provision for statistical multiplexing. 菲 Copyigh Intematinal Organizatinfor Standardization ense from IHS