G.(数字系列接口物理电气特性) 作者： 日期：2 INTERNATIONAL TELECOMMUNICATION UNIONCCITTG.703THE INTERNATIONALTELEGRAPH AND TELEPHONECONSULTATIVE COMMITTEEGENERAL ASPECTS OF DIGITALTRANSMISSION SYSTEMSTERMINAL EQUIPMENTSPHYSICAL/ELECTRICAL CHARACTERISTICSOF HIERARCHICAL DIGITAL INTERFACESRecommendation G.703Geneva, 1991FOREWORDThe CCITT (the International Telegraph and Telephone Consultative Committee) is the permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.The Plenary Assembly of CCITT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988).Recommendation G.703 was prepared by Study Group XVIII and was approved under the Resolution No. 2 procedure on the 5th of April 1991._CCITT NOTES1)In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication Administration and a recognized private operating agency.2)A list of abbreviations used in this Recommendation can be found in Annex C.ITU1991All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.个人收集整理，勿做商业用途Recommendation G.703Recommendation G.703PHYSICAL/ELECTRICAL CHARACTERISTICS OF HIERARCHICAL DIGITAL INTERFACES(Geneva, 1972; further amended)The CCITT,consideringthat interface specifications are necessary to enable the interconnection of digital network components (digital sections, multiplex equipment, exchanges) to form an international digital link or connection;that Recommendation G.702 defines the hierarchical levels;that Recommendation G.704 deals with the functional characteristics of interfaces associated with network nodes;that I.430-Series Recommendations deal with the layer 1 characteristics for ISDN user-network interfaces,recommendsthat physical and electrical characteristics of the interfaces at hierarchical bit rates be as described in this Recommendation.Note 1 The characteristics of interfaces at non-hierarchical bit rates, except n 64 kbit/s interfaces conveyed by 1544kbit/s or 2048kbit/s interfaces, are specified in the respective equipment Recommendations.Note 2 The jitter specifications contained in the following 6, 7, 8 and 9 are intended to be imposed at international interconnection points.Note 3 The interfaces described in 2 to 9 correspond to the ports T (output port) and T (input port) as recommended for interconnection in CCIR Recommendation AC/9 with reference to Report AH/9 of CCIR Study Group9. (This Report defines the points T and T.)Note 4 For signals with bit rates of n 64 kbit/s (n = 2 to 31) which are routed through multiplexing equipment specified for the 2048kbit/s hierarchy, the interface shall have the same physical/electrical characteristics as those for the 2048kbit/s interface specified in 6. For signals with bit rates of n 64 kbit/s (n = 2 to23) which are routed through multiplexing equipment specified for the 1544kbit/s hierarchy, the interface shall have the same physical/electrical characteristics as those for the 1544kbit/s interface specified in 2.1Interface at 64 kbit/s1.1Functional requirements1.1.1The following basic requirements for the design of the interface are recommended:1.1.2In both directions of transmission, three signals can be carried across the interface:64 kbit/s information signal,64 kHz timing signal,8 kHz timing signal.Note 1 The 64 kbit/s information signal and the 64 kHz timing signal are mandatory. However, although an 8 kHz timing must be generated by the controlling equipment (e.g.PCM multiplex or time slot access equipment), it should not be mandatory for the subordinate equipment on the other side of the interface to either utilize the 8kHz timing signal from the controlling equipment or to supply an 8kHz timing signal.Note 2 The detection of an upstream fault can be transmitted across the 64 kbit/s interface by transmitting an alarm indication signal (AIS) towards the subordinate equipment.1.1.3The interface should be bit sequence independent at