ITU-T M 125-1988 DIGITAL LOOPBACK MECHANISMS《数字环回机理》.pdf
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1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#%G0 ).42/$5#4)/.G0G0!.$G0G0%.%2!,G0G002).#)0,%3$)4!,G0G0,/0“!#+G0G0-%#(!.)3-3)45G134G0G0RecommendationG0G0- (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation M.125 was published in Fascicle I
2、V.1 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below).2 In this Recomm
3、endation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic ormechanical, i
4、ncluding photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.1 - Rec. M.125 1Recommendation M.125Fascicle IV.1 - Rec. M.125DIGITAL LOOPBACK MECHANISMS1 GeneralLoopback can be one of the mechanisms which may be applied to fault localization and failure detection. ThisRe
5、commendation provides digital loopback definitions and describes loopback applications related to the maintenancephases of Recommendation M.20.2 Digital loopback definitionsA digital loopback is a mechanism incorporated into a piece of equipment whereby a bidirectionalcommunication path may be conne
6、cted back upon itself so that some or all of the information contained in the bit streamsent on the transmit path is returned on the receive path.The loopback point is the location of the loopback.The loopback control mechanism is the means by which the loopback is operated and released from theloop
7、back control point.The loopback control point is the point which has the ability to directly control loopbacks.The loopback control point may receive requests for loopback operation from several loopbackrequesting points.The loopback requesting point is the point which requests the loopback control
8、point to operate loopbacks.Note 1 Loopback requests should be subject to identification and authorization.Note 2 Possible locations of loopback requesting points are: the network, or a telecommunicationsmanagement network (TMN), or a maintenance service provider (MSP).The loopback test pattern is th
9、e test information transmitted during the operation of the loopback in thechannel or channels which are to be redirected by the loopback.Note 1 The generation of the test pattern used over the loopback may or may not take place at the controlpoint.The loopback application is the maintenance phase fo
10、r which the loopback operation is used, as defined inRecommendation M.20.2.1 Loopback typesThe following three types of loopback mechanisms are defined:a) complete loopback A complete loopback is a physical layer 1 mechanism which operates on the fullbit stream. At the loopback point, the received b
11、it stream shall be transmitted back towards thetransmitting station without modification.Note The use of the term “complete loopback” is not related to implementation since such a loopbackmay be provided by means of active logic elements or controlled unbalance of hybrid transformer, etc. Atthe cont
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