ITU-T Q 108-1988 One-way or both-way operation of international circuits《国际电路的单向或双向工作》.pdf

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2、G0RecommendationG0G01 (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation Q.108 was published in Fascicle VI.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 fi

3、le are identical to the Blue Book version 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. N

4、o part of this publication may be reproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle VI.1 - Rec. Q.108 1Recommendation Q.108Fascicle VI.1 - Rec. Q.1081.8 ONE-WAY OR BOTH-WAY OPERATION

5、OF INTERNATIONAL CIRCUITS1.8.1 One-way operationIn order to have as simple as possible equipment in international exchanges and to avoid double seizures,System No. 4 has been designed in 1949-1954 for one-way operation of international circuits in semi-automatic andautomatic working.1.8.2 Both-way o

6、peration1.8.2.1 These advantages of one-way operation naturally hold good in the case of long international(intercontinental) circuits. However, for these circuits the following considerations have been determining factors inproviding both-way circuit operation:a) When a group of circuits is compose

7、d of a small number of circuits, the increase in efficiency due toboth-way operation is obviously very important. Moreover, long international (intercontinental) circuitsare very costly. Finally, the increase in the cost of terminal equipment which results from both-wayoperation is small compared wi

8、th the considerable economic advantage derived from this mode ofoperation.b) The two ends of a long international (intercontinental) group of circuits may belong to two time zoneswhich are very far apart and, depending on the difference in time, this is likely to result in important andvariable diff

9、erences between the traffic in the two directions.1.8.2.2 All circuits in System No. 5 and the speech circuits in Systems No. 6 and 7 should be equipped to work inboth-way operation. Nevertheless, the both-way method of operation would be applied only if it offered a considerableeconomic advantage.

10、Hence in the case of large groups (for example, more than 40 circuits in each direction), thepossibility of maintaining one-way operation might be considered, because of the extra reliability of this type ofoperation. If, in circumstances necessitating the use of large groups, there are great differ

11、ences between the busy hoursat each end, it would be advisable, if it were desired to maintain one-way operation, to arrange that the circuits be usedsuccessively in one or the other direction according to the time of day. This availability of the circuits for routing trafficfrom country A to countr

12、y B or vice versa would be arranged by a convenient method.In certain cases another solution is worthy of consideration. This consists of setting up three groups of circuits,two operated one-way and the third both-way, it being understood that the latter would be used as an overflow route forcalls w

13、hich could not be routed on the first two groups.1.8.2.3 Attention is drawn to the conditions which should be introduced to avoid double seizing and false blockingon both-way international circuits. In addition, attention is drawn to the fact that in semi-automatic working, as inautomatic working, a

14、ccess to the circuits at both ends should be automatic.In semi-automatic operation, in the event of double seizing, automatic selection of a new circuit should bepreferred to the operators setting up the call again, so that the operator does not become aware of the double seizing. Inautomatic operat

15、ion, automatic selection of a new circuit should naturally be the rule.The necessary arrangements have been made in the specifications of the systems concerning simultaneousseizing in both-way operation.1.8.2.4 The digital circuits in System R2 and the circuits in System R1 may be equipped to work in both-wayoperation.