The present document specifies the functional protocol for the pan-European Integrated Services Digital Network
(ISDN) as provided by European public telecommunications operators for the application to a range of supplementary
services 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) protocol.
The functional protocol is based on the use of the Facility information element and the FACILITY message, as well as
on other specific functional messages specified in clause 11.1. The protocol is symmetrical, and is applicable to both the
basic and primary rate access structures.
To be functional this protocol requires knowledge of supplementary services supported by the user equipment. This
facilitates user equipment operation without human intervention by defining semantics for the protocol elements which
user equipment can process on its own.
The procedures specified in the present document can be used for:
activation and deactivation;
invocation and operation;
interrogation;
status request; and
status notification,
of supplementary services in association with existing calls or outside any existing call.
In addition, the present document specifies the generic procedures for the channel reservation function performed by the
network as it is applied by several supplementary services (e.g. call hold).
Furthermore, the functional signalling procedures that support the delivery of notifications at the user-network interface
are covered.
The application of the present document to individual supplementary services is outside the scope of the present
document and is defined in those standards which specify the individual supplementary services.
Further parts of the present document specify the method of testing required to identify conformance to the present
document.
The pr (...abbreviated)