1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU$)4!,G0G03%#4)/.3G0G0!.$G0G0$)4!,G0G0,).%G0G03934%-3%.%2!,G0G0#/.3)$%2!4)/.3G0G0/.G0G0$)4!,).%G0G03934%-3)45G134G0G0RecommendationG0G0 (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation G.950 was publishe
2、d in Fascicle III.5 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).
3、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 by any means, electronic
4、 ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.5 - Rec. G.950 1Recommendation G.950Fascicle III.5 - Rec. G.950GENERAL CONSIDERATIONS ON DIGITAL LINE SYSTEMS(Malaga-Torremolinos, 1984; amended at Melbourne, 1988)1 IntroductionDigital line
5、systems are the means of providing digital line sections. Recommendations on digital line systemsmay recognize, for digital line sections operating at a given bit rate, specific transmission media and transmissiontechniques (e.g. coaxial cable, regenerative transmission, etc.). Performance requireme
6、nts of digital line systems are forthe guidance of systems designers and users (equipment design objectives) and may be related to hypothetical digitalpaths of defined constitution.All digital line systems operating on the same medium at a given bit rate shall comply with the characteristics ofthe d
7、igital line section at the same bit rate.2 General requirements for digital line systemsThe following general requirements apply to all digital line systems on metallic pair cables and whereapplicable with appropriate interpretation, also to those on optical fibre cables.2.1 Environmental conditions
8、2.1.1 Climatic conditionsData concerning the classification of climatic stresses that can be expected for overground equipment isavailable in IEC Publication series No. 721. Conditions for underground equipment and further details for overgroundequipment need further study.Note - Supplement No. 34 c
9、ontains some information on climatic conditions in underground repeater housing.2.1.2 PressurizationThe repeaters of digital line systems may be operated in pressurized housings.2.1.3 Protection against induced voltages and currents caused by lightning and power lines, etc.The repeaters, line termin
10、als and the power feeding arrangement should be protected against induced voltagesand currents (caused by lightning or other sources) in accordance with Recommendation K.17.The system shall be physically protected from the above induced voltages and currents so that no damage issustained. In additio
11、n, the performance of the system shall not be adversely affected by steady state induced voltages andcurrents although it may be affected by surges for the duration of the surge in certain circumstances.In addition the CCITT Directives 1 give guidance on these problems.2.1.4 Protection against inter
12、ference from other sourcesThe performance of Digital Line Systems should not be affected significantly by interference from sourceswithin stations such as fluorescent lamp, tools, ventilation plant, etc., and especially sources giving rise to pulse typeinterference. Performance degradation due to in
13、terferences from radio and broadcast transmitters should also beprevented.Note - The Supplement No. 27 contains some information on possible measures to reduce effects frominterference and measuring methods concerning interference.2 Fascicle III.5 - Rec. G.9502.1.5 Interference to other systemsCondu
14、cted and radiated emissions must not interfere with other equipment, radio and broadcast services. Inparticular, digital line systems must coexist in the same cable with other digital and analogue line systems. (Somerestrictions might, however, be necessary for joint use of different line systems on symmetrical pair cables.)Reference1 CCITT Manual Directives concerning the protection of telecommunication lines against harmful effects fromelectric power and electrified railway lines, ITU, Geneva, 1988.
