1、 O Page -O7 E 1 Recommendation T/GSI 01-07 (by correspondence, June 1987) METHOD FOR THE CHARACTERIZATION OF TELECOMMUNICATION SERVICES SUPPORTED BY AN ISDN AND NETWORK CAPABILITIES OF AN ISDN Recommendation proposed by the Special Group Integration (GSI) Text of the Recommendation adopted by the “T
2、elecommimicntiorts” Commission : “The European Conference of Posts and Telecommunications Administrations, considering - the common CEPT approach to the ISDN and general CEPT assumptions and policies for the evolution towards ISDN, - the I. Series Recommendations of the CCITT, as well as other CCITT
3、 Recommendations on ISDN, to which - the need for CEPT Administrations to have more precise answers to their specific European requirements, i.e. CEPT Administrations have contributed most significantly, to select and further define material from CCITT Recommendations, O - the need for CEPT Administ
4、rations to have as a base a comprehensive set of Recommendations, in order to promote and strengthen European harmonisation, recommends to the members of the CEPT, that they evolve their telecommunication networks towards ISDN according to the specifications given in the attached text.” Edition of O
5、ctober 31, 1987 !CEPT T/GSI*O3-07 E 7 m 232b414 0005333 3 m T/GSI O1 -07 E Page 2 1. 1.1. 1.2. 2. 3. GENERAL CONSIDERATIONS The concept and the principles of ISDNs are described in Recommendation T/GSI 01-01 i. The Recommendations in the T/GSI-02 series cover the aspects of the Telecommunication ser
6、vices sup- ported by ISDNs. The T/GSI-03 series of Recommendations deal with the aspects relating to the overall network and to network functional entities. The purpose of this Recommendation is to provide a method for the characterization of Telecommunication Services (Including supplementary servi
7、ces) and the associated Network Capabilities in an ISDN. STRUCTURE AND APPLICATION OF THE OVERALL METHOD The Recommendations for all aspects of a given Telecommunication Service are distributed according to a plan which corresponds to the overall method described below. Figure 1 (T/GSI 01-07) illust
8、rates the overall method and its applications. The development of Recommendations for new services should follow this method. THE METHOD There are three stages to the method and in each stage there are several steps. The stages are: Stage 1 is an overall service description from the users standpoint
9、. Stage 2 is an overall description of the organization of network functions to map service requirements into network capabilities. Stage 3 is the definition of switching and signalling recommendations. The steps in Stage 1 are: Step 1.1: Service Prose Dejnition and Description This step describes t
10、he service in terms of the perceptions of the user receiving the service and any other users involved in the service. It describes events in a generic form which does not constrain terminal or network design. It is intended to allow an understanding of the service without regard to implementation. T
11、he description should include operational, control, interworking and administrative aspects as wel as interactions with other services. Step 1.2: Dynamic Description of the Service Using Graphic Means The dynamic description of a service contains all the information that is sent and received by the
12、user from invocation of the service to execution of the service. The information is presented in the form of an Overall Specification and Description Language (SDL) Diagram and/or Sequence Charts. An Overall SDL chart is a ow chart which identifies all possible actions relevant to the service as per
13、ceived by the user. It treats the network as a single entity, that is, no information flows within the network are considered. A Sequence Chart is a time diagram of the events occuring in the course of a connection. Step 1.3: Static Description of the Service Using Attributes The attribute method is
14、 described in Recommendation T/GSI 01-05 2. It contains for example an outline of the attribute method and definitions of attributes. a The steps in Stage 2 are: Step 2.1 : Fiinctional Components Step 2.1 identifies from the functional component library the functional components needed to support th
15、e service. A functional component is a major unit of capability which may extend over multiple entities and services as a building block for services. The service is then constructed from the identified functional components using, in addition, elementary functions as appropriate. The use of functio
16、nal components may not be applicable in some particular application (e.g., a particularly simple service). The template and the library of Functional Components are contained in Recommendation T/GSI 03-01 3. Step 2.2: Elementary Functions Step 2.2 identifies elementary functions from the established
17、 library needed to support the service. An elementary function is a small unit of capability, located in a single node, which can be used to provide services. The service is then constructed from the identified elementary functions using, in addition, functional components, if appropriate. The templ
18、ate and the library of Elementary Functions are contained in Recommendation T/GSI 03-01 3. Edition of October 31, 1987 T/GSI O1 -07 E Page 3 Step 2.2: Elementary Functions Step 2.3 : Inforimtion Flows Information flows between functions are identified. Information flows will be in the form of sequen
19、ce charts (arrow diagrams) or Global SDL diagrams, Functional components selected from the library may already contain information flows. Step 2.4: Location of Eleinentary Functions and Fimtoitnl Coiiyoiieiits The functions required to perform a service are placed at nodes in the network. The result
20、 of the combined steps 2.3 and 2.4 is that the information flows between the nodes are specified. The Recommendation T/GSI 03-01 3 contains information about the method showing how the Elementary Functions and Functional Components are allocated to the switching and signalling nodes. The steps in St
21、age 2 are interdependent and there may be several ways of selecting combinations of network functions and functional components to satisfy a service. This process could also result, in recognition of the need for additional functional components. One application of the steps in Stages 1 and 2 may be
22、 sufficient to develop recommendations for a particular basic or supplementary service. The steps in Stage 3 are: Step 3.1: Protocols atid Formats The new messages or modified messages needed to support the new information flows between the node are identified and the detailed message elements and p
23、rocedures are designed into the relevant signalling systems. The ISDN protocol reference model is contained in Recommendation T/GSI 03-02 4. Step 3.2: Requireizertts oit Sivitchng and Service Nodes Requirements are established for each node which must provide an identified capability. The steps in S
24、tage 3 may need to be repeated for each service where different protocols and procedures apply. Step 2.1 : Functional Components - Stage 1 Step 1.1 : Service Prose Definition and Description I I Service Using Attributes Service Using Graphic Means I II Step 2.3: Information Flows H Step 2.4: Locatio
25、n of Elementary Functions and Functional Components I II I Service characterization from users viewpoint Network capabilities This term, in this context, could include some capability in the user equipment Stage 3 Step 3.2: Requirements on Switching and Service Nodes Step 3.1 : Protocols and Formats
26、 Figure 1 (T/GSI O 1-07). Graphical representation of the overall method for development of ISDN recommendations. - Edition of October 31, 1987 2- CEPT T/GSI*OL-O7 E 7 2326414 0005333 7 = - T/GSI O1 -07 E Page 4 REFERENCES i Recommendation T/GSI 01-01. Genernl on ISDN. 2 Recommendation T/GSI O 1-05. General modelling method. 3 Recommendation T/GSI 03-01, Networkjmctional principles. 4 Recommendation T/GSI 03-02. Protocole reference model. - Eaition of October 31, 1987
