ITU-T Q 44-1988 ATTENUATION DISTORTION《概述》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G02%#/-%.$!4)/.3G0G0/.G0G04%,%0(/.%37)4#().G0G0!.$G0G03).!,).).4%2.!4)/.!,G0G0!54/-!4)#G0G0!.$3%-)G13!54/-!4)#G0G07/2+).!44%.5!4)/.G0G0$)34/24)/.)45G134G0G0RecommendationG0G01 (Extract from the “LUEG0

2、“OOK)NOTES1 ITU-T Recommendation Q.44 was published in Fascicle VI.1 of the Blue Book. This file is an extract from theBlue 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 c

3、opyright 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 reproduced or

4、 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.44 1Recommendation Q.44Fascicle VI.1 - Rec. Q.44ATTENUATION DISTORTION1 Attenuation distortion1.1 All-analogue conditionsThe design

5、objectives recommended for carrier terminal equipment by the Recommendation cited in 3 aresuch that for a chain of six circuits, each equipped with a single pair of channel translating equipments in accordancewith that Recommendation, the network performance objective for the attenuation distortion

6、given by Figure 1/G.1322 will in most cases be met. The distortion contributed by the seven international centres is thereby included.Note - To assess the attenuation distortion of the international chain, the limits indicated for internationalcircuits in Recommendation G.151, 1 4 must not be added

7、to the limits for international centres mentioned inRecommendation Q.45. In fact, on the one hand, some exchange equipment would be counted twice if this additionwere made; on the other, the specification limits of Recommendation Q.45 apply to the worst possible connectionthrough an international ex

8、change, while the maintenance limits of Recommendation G.151, 1 apply to the poorestinternational circuit. The specifications of the various equipments are such that the mean performance will beappreciably better than could be estimated by the above-mentioned addition.1.2 Mixed analogue/digital cond

9、itionsIn the mixed analogue/digital period, it is expected that the attenuation/frequency characteristics of theanalogue carrier terminal equipment that is to be used in international telephone connections will continue to begoverned by existing Recommendations that are relevant to this type of circ

10、uit.Where unintegrated PCM digital processes are to be included in international telephone connections, it isrecommended that the attenuation/frequency characteristic of the bandpass filters associated with such processes shouldcomply with the more stringent version of Figure 1/G.712 5. The latter R

11、ecommendation applies specifically to caseswhere integrated PCM digital processes are associated with trunk junctions (toll connecting trunks), trunk circuits(intertoll trunks), and international circuits.With regard to the incorporation of unintegrated PCM digital processes in local telephone netwo

12、rks, therequired attenuation/frequency characteristics of the bandpass filters involved are still under study.2 The network performance objectives for the variation with frequency of transmission loss in terminalcondition of a worldwide 4-wire chain of 12 circuits (international plus national extens

13、ions), each one routed over asingle group link, are shown in Figure 1/Q.44 which assumes that no use is made of high-frequency radio circuits or3-kHz channel equipment.2 Fascicle VI.1 - Rec. Q.44References1 CCITT Recommendation Transmission losses, relative levels and attenuation distortion, Vol. II

14、I, Rec. G.141.2 CCITT Recommendation Attenuation distortion, Vol. III, Rec. G.132.3 CCITT Recommendation 12-channel terminal equipments, Vol. III, Rec. G.232, 1.4 CCITT Recommendation General performance objectives applicable to all modern international circuits andnational extension circuits, Vol. III, Rec. G.151, 1.5 CCITT Recommendation Performance characteristics of the PCM multiplex at audio frequencies, Vol. III,Rec. G.712.