1、CCITT RECNN*I-CLO (REV*L) 93 48b2593 0583233 OLb m INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU INTEGRATED SERVICES DIGITAL NETWORK (ISDN) INTERNETWORK INTERFACES 1.51 O (03/93) DEFINITIONS AND GENERAL PRINCIPLES FOR ISDN INTERWORKING ITU-T Recommendati
2、on 1.51 O (Previously ?CCIlT Recommendation?) FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The IT-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with
3、 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 Recommendatio
4、n 1.510 was revisd by the ITU-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 (), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommu
5、nication standardization Sector (ITU-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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 made in the text to references containing
6、 the acronyms “CCITT, CCIR or iFRl3” 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 sttucture. 2 telecommunication administration and a recognized operating agency. In this Rec
7、ommendation, 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 permission in writing
8、 from the ITU. CONTENTS 1 Inuodution . 2 scope . 3 Abbreviations . 4 Definitions . 4.1 Definitions related to services and network capabilities . 4.2 Definitions related to general ISDN interworking configurations 5 Telecommunication services to be supported by ISDN interworking configurations 6 ISD
9、N interworking configurations . 6.1 Reference points for network interconnections 6.2 ISDN-to-ISDN interconnection . 6.3 Interworking between ISDNs and oiher networks 6.4 ISDN internal interworking 6.5 Network concatenation configurations . Interworking functional requirements - General aspects 7.1
10、Categories of interworking functions . 7.2 Mapping principles . 7.3 Guidelines on the description of mapping functions 7.4 Functional requirements for lower layer service interworking 7.5 Functional requirements for higher layer service interworking 7 8 General aspects of selection mechanisms for in
11、terworking functions Page 1 1 2 2 2 3 3 5 5 6 7 8 8 10 10 10 11 11 11 11 Recommendation 1.510 (03/93) i CCITT RECNN*I-SLO (REV*l) 93 4862573 0581234 825 = Recommendation I510 DEFINITIONS AND GENERAL PRINCIPLES FOR ISDN INTERWORKING (Melbourne, 1988; amended at Helsinki, 1993) 1 Introdution This Reco
12、mmendation sets forth the general principles for interworking between ISDNs, between ISDNs and other networks, and internai to an ISDN. The need for interworking stems from the coexistence of existing dedicated networks with ISDNs and from the use of different, yet compatible, bearer services or tel
13、eservices for the provision of an end-to-end telecommunication service. When ISDNs are introduced, it is to be expected that most users will need to interwork with the users of other networks, especially public switched telephone networks (PSTNs), public land mobile networks (PLMNs) and dedicated da
14、ta networks. Normally, each instance of communication within an ISDN will take piace between the users of services with identical attribute values. However, communication may also take place between users of services with non-identical aribute values. In these cases interworking functions (Ms) will
15、be required. In general, when an ISDN user communicates with the user of another network, if the service perceived by the user of that other network were to be defined by the attribute method, the values would not be identical to those of the ISDN user. The purpose of interworking is to enable the u
16、sers of “different” services on an ISDN to establish a useful communication or for an ISDN user to establish a useful communication with a user of another network and vice-versa. The tem “service” in this Recommendation implies a telecommunication service as defined in Recommendation 1.210, To permi
17、t interworking, interworking capabilities, making use of MS, may be required in one or more of the following: - theISDN, - any other network involved; - customer equipment. 2 Scope This Recommendation contains the definitions and general principles to be applied in instances of ISDN interworking, wh
18、ich include interworking between ISDNs, between ISDNs and other networks, and internal to an ISDN. The ISDN interworking configurations to be considered within the scope of this Recommendation include the interconnection of two networks where at least one network is an ISDN, the concatenation of mor
19、e than two networks where an ISDN interconnects other networks (as a transit network), or the interconnection of two ISDNs by one or more other networks. ISDN interworking, as defined in this Recommendation, is considered to take place whenever end-to-end communica- tion has to be provided a) b) bet
20、ween different networks where at least one network is an ISDN; or between telecommunication services with different lower or higher layer attributes or both, where at least one of the interworking telecommunication service is supported by the ISDN; or between different networks and between telecommu
21、nication services with different lower or higher layer service attributes, or both. c) ISDN interworking, as defined in this Recommendation, is intended to cover both voice and non-voice applications. is for further study. NOTE - Interworking at layers above layer 3 of the OS1 model is not generally
22、 specified within this Recommendation and Recommendation 1.510 (0393) 1 3 CCSN CE cs CSPDN DTE ISDN IWF OSI PDN PH PLMN PS PSPDN PSTN ss N0.7 TA TE 4 4.1 Abbreviations Common channel signalling network (SS No. 7) Connection element Circuit switched Circuit switched public data network Data terminai
23、equipment Integrated services digital network Interworking function Open Systems Interconnection Public data network Packet handler Public land mobile network Packet switched Packet switched public data network Public switched telephone network Signailing System No. 7 Terminai adaptor Terminai equip
24、ment Definitions Definitions related to services and network capabilities The definitions which follow are related to services and to network capabilities. In those instances where terms already are defined in other Recommendations, appropriate references are made to such Recommendations. The follow
25、ing definitions apply to ISDN interworking: - - Bearer service in the ISDN, as defined in Recommendation 1.210 and in the 1.230-Senes Telecommunication service, as defined in Recommendation 1.210. Recommendations. Teleservice, as defined in Recommendation 1.210 and in the 1.240-Series Recommendation
26、s, provides the full capacity for communication through terminal and network lower and higher layer functions. bearer service in dedicated networks - The term bearer service in dedicated networks is characterized by a set of lower layer attributes (e.g. data transmission services, as defined in Reco
27、mmendation X.1, for use in public data networks) and corresponds to the term bearer service in an ISDN. Examples of bearer services in dedicated networks are data transmission over a data network and data transmission over the telephone network. Supplementary service, as defined in Recommendation 1.
28、210 and in the 1.250 Series Recommendations. Bearer capability, as defined in Recommendation 1.210, specifies the technical features of a bearer service in an ISDN as tbese appear to a user at the access point (S- or T- reference point). The term bearer capability also may be used with respect to de
29、dicated networks. A bearer capability does not include any terminai functions. - - - - 2 Recommendation 1.510 (03/93) CCITT RECMN*I.SLO (REVrL) 93 m 4862593 058123b bT8 W - - (No) TE. T TE 1 4.2 This subclause provides concepts and definitions of terms relevant to tbe general ISDN interworking confi
30、guration. Figure 1 depicts the scope of application of several key terms. Minitions related to general ISDN interworking configurations (Note) - ACCSS Punt d Access - 4 Resuiting scope of a bearer servioe in w 1 Resulting scope of a telesetvice in an ISDN interworking situation J TI 820450-93/DOl NO
31、TE - The TE is used to refer to either a TE1 or a TE2 plus a terminal adaptor when the network to which it is connected is an ISDN. FIGURE 1D.510 Scope da bearer service ancl a teleservice in an ISDN inerworking siaiatiOn In accordance with Figure 1, the foliowing terms are defined: interworking: Wi
32、thin the scope the ISOO-Series of Recommendations, the term Utterworking is used to express interactions between networks, between end systems, or between parts thereof, with the aim of providing a functional entity capable of supporting an end-to-end communication. The interactions required to prov
33、ide a functional entity rely on functions and on the means to select these functions. interworking functions JWFs): These functions are referred to in the Interworking definition above, which include the conversion of physical and electrical states and the mapping of protocols. An IWF may be impleme
34、nted in the ISDN, in the other network(s), at the users premises, through a third-party service provider, or in some combination of these. The IWFs needed as a result of a service requirement for interworking are categorized as connection-dependent IWFs or communication-dependent IWFs. The relations
35、hips among these terms and definitions for connection-dependent WFs and for communication-dependent IWFs are contained in Figure 2. 5 This clause contains a list of telecommunication services that are supported by interconnections between ISDNs and between ISDNs and other networks and defines the ty
36、pes of interworking functions required. The concept of 5 take into account: Telecommunication services to be supported by ISDN interworking configurations a) b) c) the definitions as outlined in 4; existing networks to be interconnected with ISDN (ISDNs, PSTNs, CSPDNs, PSPDNs, others); services to b
37、e offered with the ISDN and through interworking with ISDN. End-to-end communication may require: i) interworking at lower layers; ii) interworking at higher layers; iii) interworking at both lower and higher layers. Recommendation 1.510 (03193) 3 CCITT RECNN*I.SLO (REV* second, a connection is esta
38、blished through the PSPDN to the called terminai. The logical appearance of interworking by two-stage selection at reference point K2 (see Note 1) may be that of a customer access (see Figure 4). The application of existing interfaces and the specification of new interfaces at the KZ reference point
39、 for interworking by two-stage selection is for further study. Interworking using two-stage selection (two-stage interworking) NOTES 1 Since, in the case of interworking using two-stage selection depicted in Figure 4, no IWFs are required in the ISDN, In Recommendation X.300, examples of this catego
40、ry of interworking are defied as “interworking by port access” only reference point K2 is relevant. (see 6.2.2m.300). 2 -R SorT TE2 TA DTE - 1 - - - TEP port DTE.port FIGURE 4h.510 Inerworking by twwtage SeleCaon at reference point K, 6.2 ISDN-to-ISDN interconnection 6.2.1 Reference configuration Wi
41、th regard to ISDN-to-ISDN interworking in the context of the 1.500-Series Recommendations, the functionality required for bearer service interworking is contained in ISDN-to-ISDN internetwork interfaces. Figure 5 shows a reference configuration for ISDN-to-ISDN interworking. The services offered at
42、the endpoints may be different. ISDN-to-ISDN interworking may involve the functionality required for interworking to take place between ISDNs operated by, for instance, different Administrations. 6.2.2 Connection types Applicable Recommendation: 1.520 a) b) ZSDN circuit mode - ISDN circuit mode (bot
43、h ISDNs supporting a circuit-switched bearer service); ZSDN packet mode - ISDN packet mode (both ISDNs supporting the ISDN virtual circuit bearer service defined in Recommendation X.3 1, under case b); ZSDN packet mode - ISDN circuit mode (interworking where a packet switched bearer is requested by
44、one ISDN and a circuit switched bearer by the other ISDN); ISDN packet mode - ISDN circuit mode (interworking, where a circuit switched bearer is requested in one ISDN to obtain access to the packet handler of another ISDN for communication over an ISDN virtual circuit bearer service). c) c) 6 Recom
45、mendation 1.510 (03193) P CT* I SorT - TE 1 SorT TE- L. CT CE Comecticm element - CE, CE, Conrnfm elements of different types FIGURE 5A.510 Reference configuratioa where ISDN-bISDN iterworkiiig is required 6.3 Interworking between ISDNs and other networks 6.3.1 Reference configurations Network inter
46、working is required whenever an ISDN and a non-ISDN are interconnected to provide an end-to-end connection. Network interworking functions typically would contain the functionality needed for conversion of physical and electrical interface characteristics and for mapping of layer 2 and layer 3 netwo
47、rk protocols. Examples of such network interworking functions are: signalling conversions, information uansfer, protocol conversions, analogue-to-digital (and vice versa) conversions, and interworking between different numbering and charging plans. Two reference configurations for network interworki
48、ng are sbown in Figure 6. The services offered at the endpoints may be different. The separation between an ISDN and a non-ISDN may not always be obvious. A local exchange may, for example, support both traditional telephony service and ISDN services. The physical network components supporting these
49、 services may be inseparable. From a functional perspective, such a case might be covered by a) of Figure 6, while b) of this Figure might be more appropriate from an implementation point of view. n NOTE - Case b) illustrates the situation when no clear division exists between physical components supporting ISDN and physical components supporting PSTN. FIGURE 6D.510 Some examples of reference configurations where network interworking is required Recommendation 1.510 (03/93) 7 6.3.2 Connection types 6.3.2.1 ISDN-PSTN Applicable Recommendation: 1.530 a) ISDN circuit mode-PSTN - Spe
