1、CCITT RECMN*I-L20 (REV*L) 93 p;1 YB62591 0580469 T19 D INTERNATIONAL TELECOMMUNICATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE 1.1 20 (03/93) INTEGRATED SERVICES DIGITAL NETWORKS (ISDNs) ITU-T Recommendation 1.1 20 (Pr
2、eviously “CCITT Recommendation”) CCITT RECMN*I.120 (REVxL) 93 I 4862593 0580470 730 = FOREWORD The ITU Telecommunication Standardization Sector (IT-T) is a permanent organ of the iternational Telecom- munication Union. The IT-T is responsible for studying technical, operating and tariff questions an
3、d issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendation
4、s on these topics. IT-T Recommendation 1.120 was revised by the IT-T Study Group XVIII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 Februa
5、ry 1993. In its place, the IT Telecommunication Standardization Sector (IT-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been mad
6、e in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a rec
7、ognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O IT 1993 All 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 micr
8、ofilm, without permission in writing from the IT. CCITT RECPlN*I-320 (REV*L) 73 LIB62573 0580473 b77 = CONTENTS Page 1 Principles of ISDN . 1 2 Network evolution towards ISDN . 1 3 Evolution of ISDNs 2 Recommendation 1.120 (03/93) i CCITT RECMN*I=328 (REV*L) 93 IPCI 4862593 0580472 503 W Recommendat
9、ion 1.120 INTEGRATED SERVICES DIGITAL NETWORKS (ISDNs) (Malaga-Torremolinos, 1984; amended at Helsinki 1993) 1 Principles of ISDN 1.1 The main feature of the ISDN concept is the support of a wide range of voice and non-voice applications in the same network. A key element of service integration for
10、an ISDN is the provision of a range of services using a limited set of connection types and multipurpose user-network interface arrangements. 1.2 connections in an ISDN include both circuit-switched and packet-switched connections and their concatenations. ISDNs support a variety of applications inc
11、luding both switched and non-switched connections. Switched 1.3 64 kbit/s switched digitai connections. As far as practicable, new services introduced into an ISDN should be arranged to be compatible with 1.4 An ISDN will contain intelligence for the purpose of providing service features, maintenanc
12、e and network management functions. This intelligence may not be sufficient for some new services and may have to be supplemented by either additional intelligence within the network, or possibly compatible intelligence in the user terminals. 1.5 A layered protocol structure should be used for the s
13、pecification of the access to an ISDN. Access from a user to ISDN resources may vary depending upon the service required and upon the status of implementation of national ISDNs. 1.6 situations. It is recognized that ISDNs may be implemented in a variety of configurations according to specific nation
14、al 1.7 Based on these principles the I-Series Recommendations have been developed. Figure 1 provides a broad outline of the structure of the I-Series of Recommendations and their relationship to other Recommendations. As shown in Figures, the current structure of the I-Series documentation is subdiv
15、ided into seven major parts. other I-Series documents may be added as the need arises. In addition, to support the implementation of the ISDN concepts, Recommendations have been produced and others wiil be produced in other series by the appropriate specialist group. 2 Network evolution towards ISDN
16、 2.1 ISDNs are based on the concepts developed for telephone IDNs and may evolve by progressively incorporating additional functions and network fatures including those of any other dedicated networks such as circuit-switching and packet-switching for data so as to provide for existing and new servi
17、ces. 2.2 The transition from an existing network to a comprehensive ISDN may require a period of time extending over one or more decades. During this period arrangements must be developed for the interworking of services on ISDNs and services on other networks. 2.3 In the evolution towards an ISDN,
18、digitai end-to-end connectivity will be obtained via plant and equipment used in existing networks, such as digital transmission, time-division multiplex switching and/or space-division multiplex switching. Existing relevant Recommendations for these constituent elements of an ISDN are contained in
19、the appropriate series of Recommendations of CCm and of CCIR. 2.4 In the early stages of the evolution of ISDNs, some interim user-network arrangements may need to be adopted in certain countries to facilitate early penetration of digital service capabilities. Arrangements corresponding to national
20、variants may comply partly or wholly with I-Series Recommendations. However, the intention is that they will not be specifically included in the I-Series. Recommendation 1.120 (OY93) 1 3 Evolution of ISDNs An evolving ISDN may also include switched connections at bit rates higher and lower than 64 k
21、bit/s. Recommendation 1.121 gives the broadband aspects of ISDN. Usemetwork interface aspects Other Recommendations Recommendations in the E, F,G, H,Q,S,T,V,X,etc., Series covering character- isw of particuhr edsting and future networks and elements NOTE - Models, reference configurations, tools, methods, are contained in the appropriae I-Series Recommendations. FIGURE 1A.120 Shcture 0fISeries Recommendatiois and their relationship with other Recommendations 2 Recommendation 1.120 (OW3)
