scope:

The present document specifies the stage three of circuit-mode on-demand basic telecommunication services for the pan-European Integrated Services Digital Network (ISDN) as provided by European telecommunications operators at the T reference point or coincident S and T reference point (as defined in ITU-T Recommendation I.411 [3]) by means of the Digital Subscriber Signalling System No. one (DSS1). Stage three identifies the protocol procedures and switching functions needed to support a telecommunication service (see CCITT Recommendation I.130 [2]).

In addition, the present document specifies the protocol requirements at the T reference point where the service is provided to the user via a private ISDN.

NOTE 1: Procedures at the T reference point, to support the access of a private ISDN to the public ISDN, are not explicitly identified in this standard, however some procedures are applicable only to the T reference point.

The present document does not specify the additional protocol requirements where the service is provided to the user via a telecommunication network that is not an ISDN.

The present document is specified using the Specification and Description Language (SDL) as specified in CCITT Recommendation Z.100 [4].

In order to describe the point-to-multipoint operation of the protocol, the concept of a "global" process running in parallel with a number of "individual" (dynamic) processes has been introduced. This approach, and the associated definition of internal primitives is intended to provide a coherent description of the protocol and does not constrain implementations. The SDL diagrams in this part, and the text of clause 5 of ETS 300 403-1 [1], together provide a complete specification of the protocol within the scope of the present document.

A basic telecommunication service is a fundamental type of service. It forms the basis on which supplementary services may be added.

NOTE 2: Specific requirements of individual circuit-mode basic telecommunication services are not covered in the present document. However, ETR 018 [5] gives guidance on the use of service specific information elements to implement individual basic telecommunication services.

The method of testing of the present document is common with that for ETS 300 403-1 [1]. Further parts of the present document specify the method of testing and detailed application specific requirements to determine conformance based on the present document.

The present document is applicable to equipment supporting circuit-mode on-demand basic telecommunication services, to be attached at either side of a T reference point or coincident S and T reference point when used as an access to the public ISDN.