1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 5 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(G0G037)4#().3).!,).G0G0/6%2G0G02!$)/G0G0!.$G0G0-5,4)0,%8%$#(!%,3/0%2!4/2G0G02%#!,G0G0/.G0G0!G0G04%,%8G0G0#!,3%4G0G050G0G0/.G0G0!G0G02!$)/4%,%2!0(G0G0#)2#5)4)45G134G0G0RecommendationG0G05 (Extract from
2、 the “LUEG0“OOK)NOTES1 ITU-T Recommendation U.21 was published in Fascicle VII.2 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 v
3、ersion and copyright conditions remain unchanged (see below).2 In this Recommendation, 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 r
4、eproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle VII.2 - Rec. U.21 1Recommendation U.21Fascicle VII.2 - Rec. U.21OPERATOR RECALL ON A TELEX CALL SET UPON A RADIOTELEGRAPH CIRCUIT(New
5、Delhi, 1960: amended at Geneva. 1964)The CCITT,considering(a) that experience has shown that, for telex calls set up over a radiotelegraph circuit, it was useful to enablethe telex subscriber to cause an operator to re-enter on a call in progress without interrupting it;(b) that such re-entry may be
6、 of interest in the following cases as well as in the case of a defective connection:i) When a subscriber decides, in the course of a call, to change from a plain text to a cypher he can call theoperators in the terminal radio exchanges and ask them to interrupt the delay signal, which might otherwi
7、sedisturb the synchronism between the cyphering apparatus used at the two ends.ii) When a subscriber has sent a message but waits a very long time for a reply from his correspondent, he canask the operator whether his message is still being stored or whether it is expected that any interruption toth
8、e radio circuit will continue. If need be, he can then choose another means of communication (telegramor telephone call) to send an urgent message to its destination;(c) that although it seems that re-entry by an operator will be limited mainly to national networks (for exampleby a subscriber callin
9、g the controlling telex operator on the radiotelegraph circuit), international standardization of anoperator recall signal would be useful if the controlling telex operator on the radiotelegraph circuit is located in atransit country, and also for intermediate manual switches; this would no doubt pr
10、ove to be a great advantage when thispossibility is generally utilized,unanimously declares thefollowing view(1) If the Administrations concerned agree on the use of a special signal enabling a subscriber to recall aninternational telex operators position making use of radiotelegraph circuits, such
11、a recall must not cause release of acall in progress.(2) This operator recall signal will consist of the following sequence: combinations No. 28 (line-feed)followed by four combinations No. 27 (carriage-return).(3) The detection device causing re-entry by the operator will be controlled by the recei
12、pt of four consecutivecombinations No. 27; combinations No. 28 will only be used to avoid superposition of the text on the receivingteleprinter and will not have to be recognized by the detection device.(4) The equipment for discriminating the operator recall signal will be switched off by a sequence of fourconsecutive combinations No. 19 (signal for transfer to data).
