1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G0,%!3%$G0G0#)2#5)43#(!2!#4%2)34)#3G0G0/&G0G0/2$).!29G0G015!,)49).4%2.!4)/.!,G0G0,%!3%$G0G0#)2#5)43)45G134G0G0RecommendationG0G0- (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommend
2、ation M.1040 was published in Fascicle IV.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 version and copyright conditions remai
3、n 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 reproduced or utilized in any form or
4、by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.2 - Rec. M.1040 1Recommendation M.1040Fascicle IV.2 - Rec. M.1040CHARACTERISTICS OF ORDINARY QUALITY INTERNATIONALLEASED CIRCUITS1)1 ScopeThis Recommendation details th
5、e characteristics of international leased circuits for telephony and otherpurposes that do not require the use of special quality leased circuits conforming to either Recommendation M.1020 orRecommendation M.1025.2 Characteristics2.1 Nominal overall lossBecause of the differing nominal level at rent
6、ers premises due to the various national practices, it is notnormally possible to predict the nominal overall loss of the circuit at the reference frequency. Only exceptionally can apredetermined specified nominal overall loss at the reference frequency between renters installations be offered toren
7、ters and then only after prior consultation among the Administrations concerned.For 4-wire circuits the receiving relative level at the renters premises should not be lower than 15 dBr. If amean sending signal power of 15 dBm0 is assumed, the resulting minimum received power (30 dBm) is sufficient f
8、ortelephony and the other purposes for which circuits to this Recommendation are intended. Should these circuits be usedfor other purposes, higher receiving relative levels may be required in some circumstances. Reference should be made toSupplement No. 2.16 to Volume IV (Fascicle IV.3).It should be
9、 noted that the overall loss in each direction of transmission may not have the same value.2.2 Loss/frequency distortionThe provisional limits for the overall loss relative to that at 1020 Hz for the circuit between rentersinstallations are given in Figure 1/M.1040.2.3 Random circuit noiseThe level
10、of the psophometric noise power at a renters premises depends upon the actual constitution of thecircuit, in particular upon the length of frequency division multiplex carrier systems in the circuit. The provisional limitfor leased circuits of distances greater than 10 000 km is 38 dBm0p. However, c
11、ircuits of shorter length will havesubstantially less random noise (see also Annex A to this Recommendation and Recommendation M.1050, 3.5)._1)The application of this Recommendation to multiterminal leased circuits is intended only for radial networks in which thesespecifications are to be met betwe
12、en a designated central station and each of the outlying stations. It does not apply tomultiterminal conference networks between any two stations.2 Fascicle IV.2 - Rec. M.1040d01-scFIGURE 1/M.1040.D01ANNEX A(to Recommendation M.1040)Random circuit noiseFigure A-1/M.1040 displays random noise versus
13、length of circuit of FDM carrier systems and is presented asa guide to the random noise performance which may be found on an international leased circuit.d02-scFIGURE A-1/M.1040.D02Fascicle IV.2 - Rec. M.1040 3Note At the present time the section of the circuit provided by satellite (between earth s
14、tations) employingFDM techniques contributes approximately 10 000 pW0p (50 dBm0p) of noise. Therefore, for the purpose ofdetermining maintenance limits for noise measurement on leased circuits, the length of this section may be considered tobe equivalent to 1000 km in Figure A-1/M.1040.The contribution to noise of a circuit section provided by a satellite employing TDM techniques remains as asubject for further study.
