1、CCITT RECMN*I=570 93 m 4Bb259L 0577377 885 m INTERNATIONAL TELECOMMUNICATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU INTEGRATED SERVICES DIGITAL NETWORK (ISDN) INTERNETWORK INTERFACES 1.570 (03/93) PUBLWPRIVATE ISDN INTERWORKING ITU-T Recommendation 1.570 (Previously “CCIll Reco
2、mmendation”) CCITT RECMN*I=570 33 m 4862533 0577378 733 m FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations
3、 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 Recommendations on these topics. ITU-T
4、Recommendation 1.570 was prepared by the ITU-? 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 February 1993. In its place,
5、 the ITLJ Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB bave been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to re
6、ferences 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 recognized operating a
7、gency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 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 microfilm, without per
8、mission in writing from the ITU. CONTENTS Page 1 Scope and objectives 2 Definitions . 3 Reference configurations 4 Scenarios for public/private ISDN interworking . 5 Service interworking 5.1 Introduction 5.2 Service provision concept 5.3 Publichvate ISDN configurations . 5.4 Interworking requirement
9、s Inkworking requirements at point of interconnection . 6 1 1 1 3 4 4 4 5 5 7 Recommendation 1.570 (03/93) 1 CCITT RECMN*I-570 93 48b259L 0577180 37T Recommendation 1.570 PUBLICRRIVATE ISDN INTERWORKING (Helsinki, 1993) 1 Scope and objectives Recognizing that the CCITT Recommendations on ISDN apply
10、to public ISDNs and may apply to private ISDNs, there is a need to ensure smooth service interworking across public and private ISDNs such that the services provided are transparent to the user across the public and private network components. This Recommendation aims to provide general principles a
11、nd guidelines for the interworking of public and private ISDNs. The following objectives are envisaged in the development of Recommendations on public/private ISDN interworking: 1) the provision of common compatible functionality to provide common ISDN services; 2) the provision of end-to-end (El-ty
12、pe) ISDN terminal connectivity as well as terminal interchangeability; 3) a common overall ISDN transmission plan. 2 Definitions public network: A network which provides services to the general public. private network: A network which provides services to a specific set of users only. mixed publidpr
13、ivate ISDN: An overall ISDN which consists of any concatenation of public and private networks. The user perspective of the services offered by a mixed public/private ISDN is common and consistent across the public and private network components of the mixed network. customer network: A network conn
14、ected at the user side to the public ISDN and operated based on the subscription to public ISDN services offered at the T reference point (1.e. the so-called customer access point 1 according to Recommendation 1.210). NOTE -The above definitions do not include legal or regulatory aspects and do not
15、indicate any aspect of ownership. Network - see Recommendation I. 1 12, item 305. ser - see Recommendation 1.1 12, item 401. Customer equipment - see Recommendation 1.1 12 item 480. 3 Reference configurations Recommendation 1.41 1 describes the functional groups and reference configurations for the
16、customer network, while Recommendation 1.412 describes the interface structures to be used at reference points S and T. Figure 1 illusuates this overall division of functions involved in a communication across the ISDN. Recommendation 1.570 (03/93) 1 T I- + I- * Customer network Public ISDN I- IT Cu
17、stomer , I (c network I Overall ISDN-connection NOTES 1 2 and T reference points. 3 Recommendation 1.430 as the public ISDN does, the ISDN connection ends at the S reference point as shown in Figure 2. The functional group customer network is described in Recommendation 1.41 1. ifthe customer networ
18、k is null (Le. null NT2) the ISDN connection can be considered to end at coincident S Ifthe customer network is an ISPBX-based network, providing the same ISDN connection types according to FIGURE 1/1.570 General ISDN reference configuration T I- /- - ISPBXpriate Public ISDN )+I ISDN s I- I / -_ .-/
19、 -_I T181324Ci911d02 Overall ISDN-connection NOTES 1 This reference configuration applies to the case where the customer network consists only of ISPBXs. The case in which “IS-CENTREXs” are included is for further study. 2 Other configurations are possible where the call is asymmetrical, or terminat
20、es in or involves high layer functions. 3 The terms “customer equipment” and “public ISDN” do not presuppose a particular regulatory situation in any country and are used purely for technical reasons. The connection type concept is defined in Recommendation 1.340. FIGURE 2/1.570 Overall ISDN referen
21、ce configuration for a mixed ISPBWpublic ISDN scenario 2 Recommendation 1.570 (03/93) CCITT RECMN*I*570 93 4862591 0577382 342 9 4 In the overlay scenario, the connection, which is established through the public ISDN, is treated as a private ISDN-to- private ISDN link (link B in Figure 3). Signallin
22、g andor user information which is carried on link B is transparent to the public ISDN. In this case, the services available to a TE are those offered by the private ISDN, as if they were provided via link A. Scenarios for publidprivate ISDN interworking TE Private ISDN Link A TE T181325091/603 FIGUR
23、E 3/1.570 Overlay scenario For the concatenated case (see Figure 4) interworking is required at the user-network access of the public ISDN, i.e. at links i and 3. In this case, the services provided to a TE are realized by the cooperation of functions and capabilities provided by both the public and
24、 private network. Private ISDN A Private ISDN B QQ Link 1 Link 3 Public ISDN FIGURE 4/1.570 Concatenation scenario Recommendation 1.570 (03/93) 3 CCITT RECflNrI-570 93 W 4862593 0577383 O89 W The functionality of an overlay scenario may be achieved by upgrading a concatenation scenario by means of v
25、irtual private network (VPN) features. Virtual private ISDNs may support features such as uniform numbering plan, specialized routing, account codes, and extension dialling. Also the efficiency of user information transfer may be improved e.g. by the provision of A-law/p-law conversion, echo cancell
26、ation, etc. The VPN concept and its relationship to the overlay and concatenation scenarios require further study. NOTE -The overlay scenario (Figure 3) is not currently addressed in 5 and 6 of this Recommendation. 5 Service interworking 5.1 Introduction The following public/private ISDN interworkin
27、g principles are identified : i) In a mixed publidprivate ISDN, the stage 1 service descriptions should provide views of the service for both the S and T reference points, and these views may be different. Where S and T reference points are coincident, one view of the service applies. Additional req
28、uirements for the service definition at the T reference point, if any, should be separately identified. For each service, several scenarios may be possible for the actual physical location of logical functionality to the public ISDN. The range of scenarios supported by the public ISDN needs to be id
29、entified (by stage 2 service descriptions). iii) For some services and a particular private ISDN, the specific scenarios that are applicable with respect to physical allocation of functionality should be negotiated and agreed to between the public ISDN and the private ISDN at subscription time. For
30、other services, additional signalling capabilities shall provide the necessary information. ii) Service-specific requirements are defined and described in the 1.200-Series of Recommendations. 5.2 Service provision concept Service interworking aspects between public ISDNs and private ISDNs shall be s
31、pecified at the T reference point. Basic bearer services and bearer capabilities as used in the context of teleservices and supplementary services may be supported independently by the private and public ISDN. Where calls pass through a public and a private ISDN: - - both networks will be involved i
32、n the provision of basic services, both networks will share their involvement in the provision of Supplementary services. The degree of involvement for each ISDN varies, depending on the basic or supplementary service concerned. The involvement of public and private ISDNs shall be indicated in each
33、service description by one of the following categories: - Local, if only one ISDN is involved. This can be with or without notification to the remote party, and both ISDNs shall be capable of conveying such notifications. A local involvement can also occur in both networks simultaneously. For exampl
34、e, the invocation of the public ISDN service by the private ISDN at the T reference point can enable the private ISDN to offer the service at the S reference point. This is classified “double“. Cooperative, if both ISDNs are involved. This case requires cooperation between both ISDNs, whose function
35、s will be complementing each other. - Depending on the actual routing of a call, some services need to be classified in both categories. As a consequence of the cooperation between the public and private ISDN in providing common services in mixed private/public calls, the information exchanged at th
36、e T reference point between two ISDNs may be different from what is exchanged between terminals and either ISDN at the S, and S and T coincident reference points. 4 Recommendation 1.570 (03/93) CCITT RECMN*I.570 73 Li662571 0577LBrl TL5 M Therefore, the service descriptions of the public ISDN shall,
37、 where appropriate, take into account these two types of customer configurations. 5.3 Publiflrivate ISDN configurations Conceptually, there is a single connection at the T reference point between a public and a private ISDN. However, in practice, there can be more than one instance of a T reference
38、point (see Figure 5) because: - - - a private ISDN can be connected to more than one public ISDN; a private ISDN exchange can be connected to more than one public ISDN exchange; a public ISDN exchange can be connected to more than one private ISDN exchange. Public ISDN A I Exchange I I Exchange I T1
39、813270-91/dO5 FIGURE 5A.570 Example of a public/private ISDN configuration NOTE 1 - Unless explicitly stated otherwise, the termination of the accesses of one private ISDN exchange on different local exchanges of the public ISDN shall not be assumed. If the grade of service for intercommunication be
40、tween a public and a private ISDN requires more than one basic and/or primary rate access to be provided, public ISDNs shall offer the possibility to combine the B- and D-channels of these accesses to one or more trunk group(s), see T3.1 and T3.2 in Figure 5. NOTE 2 - The possibility of more than on
41、e trunk group between two exchanges is useful for a number of operational and management purposes, e.g. to reserve certain accesses for particular purposes. The description of these purposes is outside the scope of this Recommendation. As a subscription option, single or multiple collective number(s
42、) shall be assigned to a trunk group. From a numbering point of view all B- and D-channels of an entire mnk group may form one or multiple bundles. 5.4 Interworking requirements 5.4.1 Numbering 5.4.1.1 Use of numbering plans The public ISDN shall employ the ISDN numbering plan for ISDN era (see Reco
43、mmendation E.164). The private ISDN can employ either an E. 164 format plan or a private numbering plan or both numbering plans. i) The term “trunk group” refers to trunks of private ISDN exchanges, not local exchanges of the public ISDN. Recommendation 1.570 (03/93) 5 For calls tohorn a public ISDN
44、, numbers of the E.164 plan are normally used (Note). In addition, numbers of other CCIT specified numbering plans, e.g. X.121, may appear in certain interworking situations. Interworking between numbering plans is defined in Recommendation E.166BC.122. Arrangements other than those defined therein
45、will be subject to subscription arrangements supported by the public ISDN. NOTE - Numbers in an “unknown” numbering plan may also be used, in particular when a prefm or an escape code is present (see Recommendation 4.931 for definition and use if “unknown” numbering plan). In this case the number mu
46、st be organized according to the public network dialling plan. If the public ISDN supports private numbering plans and the private ISDN subscribes to a service that makes use of such plans, numbers of a private ISDNs numbering plan may appear at the T reference point. 5.4.1.2 Screening and non-scree
47、ning arrangement Public and private ISDN shall be responsible for the correctness of identification numbers, Le. they shall determine identities within their respective domains, or at least, verify identity numbers offered them by their terminals. Any interchange of identification numbers, which mig
48、ht be used in the context of supplementary services, will be subject to applicable screening arrangements between the public and private ISDN. If identification numbers (e.g. calling line, connected line, forwarding numbers, etc.) are offered by a private ISDN to a public ISDN, one of the following
49、two arrangements applies: a) Screening arrangement As a standard connection arrangement, the public ISDN may apply screening of identification numbers offered by a private ISDN. If the identification number provided by the private ISDN is valid and the check is successful, this number is used by the network. If the check is unsuccessful, the public ISDN will assign the default E. 164 number for the private ISDN. b) Non-creening arrangement Based on subscription to a special connection arrangement, the public ISDN will not apply screening of identification numbe
