1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU$)4!,G0G03%#4)/.3G0G0!.$G0G0$)4!,G0G0,).%G0G03934%-3%.%2!,G0G0#/.3)$%2!4)/.3G0G0/.G0G0$)4!,3%#4)/.3G0G0!.$G0G0$)4!,G0G0,).%G0G03934%-3)45G134G0G0RecommendationG0G0 (Extract from the “LUEG0“OOK)NOTES1 ITU-T Reco
2、mmendation G.901 was published 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
3、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 utilized in any for
4、m or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.5 - Rec. G.901 1Recommendation G.901Fascicle III.5 - Rec. G.901GENERAL CONSIDERATIONS ON DIGITAL SECTIONSAND DIGITAL LINE SYSTEMS(Geneva, 1980; further amended)1
5、Digital sections and digital systemsThe term digital section is used in these Recommendations as a general term to include digital line section anddigital radio section. This term is defined in Recommendation G.701 (see also Figure 1/G.701 and Figure 2/G.960).Digital sections are defined as componen
6、t parts of digital links operating at particular bit rates and may be regarded as“black boxes“. For digital sections used in digital hierarchy (network) applications the inputs and outputs arerecommended in the form of “equipment interfaces“ (i.e. in Recommendation G.703 for hierarchical bit rates o
7、r in theRecommendation G.931 for non-hierarchical bit rates). For digital sections used for ISDN customer access the “sectionboundaries“ are at the T reference point and the appropriate V reference point. User-network interfaces which may beused at the T reference point are recommended in the I.400
8、series of Recommendations and the exchange interfaceswhich may be used at the V reference points are recommended in the Q.500-Series of Recommendations. Digital sectionRecommendations contain the common network-related requirements applicable to digital radio, metallic and opticaltransmission system
9、s. The performance requirements relate to network performance objectives.Digital line and radio systems are the means of providing digital sections. Recommendations on digital line andradio systems may recognize, for digital sections operating at a given bit rate, specific transmission media andtran
10、smission techniques. Performance requirements of digital line and radio systems are for the guidance of systemdesigners (equipment design objectives) and may be related to hypothetical reference digital sections of definedconstitution.All digital line and radio systems operating at a given bit rate
11、and for use in a particular part of the networkshall comply with the characteristics of the digital section appropriate for that network application.Digital radio system requirements are covered in CCIR Recommendations.2 International interconnectionsFor international interconnections CCITT recommen
12、ds:1) as preferred solution interconnections at equipment interfaces operating at hierarchical bit rates, theconnections shown in Figures l a)/G.901 and 2 a)/G.901;2) as second priority solution interconnections at equipment interfaces operating at non-hierarchical bit rates,the connections shown in
13、 Figure 2b)/G.901;3) that line interfaces as indicated in Figure 1b)/G.901 and Figure 2c)/G.901 are not intended to be used asinternational interconnection points.All parameters necessary for interconnection at equipment interfaces will be covered by that part of theRecommendation that deals with “C
14、haracteristics of digital line sections“.Equipment interfaces as used in the following Recommendations refer to interfaces as specified inRecommendation G.703 and may either refer to a direct connection between terminating equipments or to a connectionat a digital distribution frame.2 Fascicle III.5
15、 - Rec. G.901 Fascicle III.5 - Rec. G.901 33 ISDN customer accessDigital sections and digital line systems for the ISDN customer access are recommended specifically for thoseapplications and are not part of the “digital hierarchy“. Whereas other digital section and digital line systemRecommendations
16、 are symmetrical (i.e. the line terminations have the same functionality at each end), those for theISDN customer access are asymmetrical in respect of certain functions (i.e. bit timing, octet timing,activation/deactivation, power feeding, operations and maintenance). This is because of the inherent asymmetry of thelocal line distribution network and different requirements of exchange interfaces to user-network interfaces.BibliographyCCITT Recommendation Transmission performance objectives and Recommendations, Vol. III, Rec. G.102.
