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 ITU-T 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 the present document, 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
ITU-T 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.
(...abbreviated)