1、CCITT REMCN*I-121 91 = 4862591 0563093 2 - ._ . INTERNATIONAL TELECOMMUNICATION U NION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES 1.1 21 BROADBAND ASPECTS OF ISDN Recommendation 1.1 21 -
2、 Geneva, 1991 CCITT REflCN*I*121 91 = 48b2571 0561074 4 F FOREWORD The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and iss
3、uing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCIT 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
4、CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988). Recommendation 1.121 was prepared by Study Group XVIII and was approved under the Resolution No. 2 procedure on the 5th of April 1991. CCIT NOTES 1) telecommunication Administration an
5、d a recognized private operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a 2) A list of abbreviations used in this Recommendation can be found in Annex A. o ITU 1991 All rights reserved. No part of this publication may be reproduced or
6、 utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE INTEGRATED SERVICES DIGITAL NETWORK (ISDN) G
7、ENERAL STRUCTURE AND SERVICE CAPABILITIES 1.1 21 BROADBAND ASPECTS OF ISDN Recommendation 1.121 Geneva, 1991 c CCITT REMCN*I-323 73 M 4862573 05b307b 8 M Preamble to B-ISDN Recommendations In 1990, CCITT SG XVIII approved a first set of Recommendations on 3-ISDN. These are: I. 113 - Vocabulary of te
8、rms for broadband aspects of ISDN 1.121 -Broadband aspects of ISDN I. 150 - B-ISDN asynchronous transfer mode functional characteristics 1.21 1 - B-ISDN service aspects 1.3 11 - B-ISDN general network aspects 1.321 - B-ISDN Protocol Reference Model and its application 1.327 - B-ISDN functional archi
9、tecture 1.361 - B-ISDN ATM Layer specification 1.362 - B-ISDN ATM Adaptation Layer (AAL) functional description 1.363 - B-ISDN ATM Adaptation Layer (AAL) specification 1.413 - B-ISDN user-network interface 1.432 - B-ISDN user-network interface -Physical Layer specification 1.610 - Operation and main
10、tenance principles of B-ISDN access These Recommendations address general B-ISDN aspects as well as specific service- and network-oriented issues, the fundamental characteristics of the asynchronous transfer mode (ATM), a first set of relevant ATM oriented parameters and their application at the use
11、r-network interface as well as impact on operation and maintenance of the B-ISDN access. They are an integral part of the well established I-Series Recommendations. The set of Recommendations are intended to serve as a consolidated basis for ongoing work relative to B-ISDN both within CCITT and in o
12、ther organizations. They may also be used as a first basis towards the development of network elements. CCIT will continue to further develop and complete these Recommendations in areas where there are unresolved issues and develop additional Recommendations on B-ISDN in the I-Series and other serie
13、s in the future. CCITT REMCN*I=L21 91 4862593 05b1097 T _ 1 Recomrnenda tion I. 121 BROADBAND ASPECTS OF ISDN (revised 1990) O Foreword This Recommendation states the basic principles of broadband aspects of integrated services digital network (B-ISDN) and indicates further developments of the ISDN
14、network capabilities in order to support more advanced services and applications. The B-ISDN Recommendations were written taking into account the following: - - - - - - - - the emerging demand for broadband services; the availability of high speed transmission, switching and signal processing techno
15、logies; the improved dafa and image processing capabilities available to the user; the advances in software application processing in the computer and telecommunication industries; the need to integrate both interactive and distribution services; the need to integrate both circuit and packet transfe
16、r mode into one universal broadband network; the need to provide flexibility in satisfying the requirements of both user and operator; the need to cover broadband aspects of ISDN in CCIIT Recommendations. 1 General 1.1 The main feature of the ISDN concept is the support of a wide range of audio, vid
17、eo and data applications in the same network. A key element of service integration for an ISDN is the provision of a wide range of services to a broad variety of users utilizing a limited set of connection types and multipurpose userbetwork interfaces. 1.2 rn the context of this Recommendation, the
18、term B-ISDN is used for convenience in order to refer to and emphasize the broadband aspects of ISDN. The intent, however, is that there be one comprehensive notion of an ISDN which provides broadband and other ISDN services. 2 Principles of B-ISDN 2.1 Asynchronous transfer mode (ATM) is the transfe
19、r mode for implementing B-ISDN and is independent of the means of transport at the Physical Layer. 2.2 B-ISDN supports switched, semi-permanent and permanent, point-to-point and point-to-multipoint connections and provides on demand, reserved and permanent services. Connections in B-ISDN support bot
20、h circuit mode and packet mode services of a mono- and/or multimedia type and of a connectionless or connection-oriented nature and in a bidirectional or unidirectional configuration. 2.3 independent. 2.4 A B-ISDN will contain intelligent capabilities for the purpose of providing advanced service ch
21、aracteristics, supporting powerful operation and maintenance tools, network control and management. Further inclusion of additional intelligent features has to be considered in an overall context and may be allocated to different networkherminal elements. The B-ISDN architecture is detailed in funct
22、ional terms and is, therefore, technology and implementation Recommendation 1.121 1 CCITT REMCN*I.3Z3 91 W 48b2593 0563098 3 2.5 Since the B-ISDN is based on overall ISDN concepts, the ISDN access reference configuration is also the basis for the B-ISDN access reference configuration. 2.6 A layered
23、structure approach, as used in established ISDN protocols, is also appropriate for similar studies in B-ISDN. This approach should also be used for studies on other overall aspects of B-ISDN including information transfer, control, intelligence and management. 2.7 Any extension of network capabiliti
24、es or change-in network performance parameters will not degrade the quality of service of existing services. 2.8 The evolution to B-ISDN should ensure the continued support of existing interfaces and services. 2.9 New network capabilities will be incorporated into B-ISDN in evolutionary steps to mee
25、t new user requirements and accommodate advances in network developments and progress in technology. 2.10 It is recognized that B-ISDN may be implemented in a variety of ways according to specific national situations. 3 Characteristics of an ATM-based B-ISDN The underlaying asynchronous transfer mod
26、e (ATM) of the B-ISDN provides some specific, advantageous facilities: - - - high flexibility of network access due to the cell transport concept and specific cell transfer principles; dynamic bandwidth allocation on demand with a fine degree of granularity; flexible bearer capability allocation and
27、 easy provision of semipermanent connections due to the virtual path concept; independence of the means of transport at the Physical Layer. - 4 Evolution 4.1 B-ISDN will be based on the concepts developed for ISDN and may evolve by progressively incorporating directly into the network additional B-I
28、SDN functions enabling new and advanced services. 4.2 The deployment of B-ISDN may require a period of time extending over one, or more, decade) as operators seek to find the most economic means of evolving to the B-ISDN. These evolutionary phases (e.g. deployment of metropolitan area networks, pass
29、ive optical networks, local area networks and also satellite based networks) will need to be harmonized with the overall B-ISDN concepts ensuring the continued support of existing interfaces and services and be eventually integrated with the B-ISDN. In these evolutionary phases appropriate arrangeme
30、nts must be developed for the interworking of services on B-ISDN and services on other networks. 4.3 In the evolution towards a B-ISDN, some digital end-to-end connections may in part use digital transmission and switching equipment that has not been optimized for the B-ISDN, e.g. G.702 plesiochrono
31、us digital hierarchy transmission systems. Such connections may provide a reduced maximum service bit rate at the user-network interface (UNI). ANNEXA (to Recommendation 1.121) Alphabetical list of abbreviations contained in this Recommendation ATM Asynchronous transfer mode B-ISDN Broadband aspects of integrated services digital network 2 Recommendation 1.121
