This International Standard specifies the signalling protocol for the support of the Simple Dialog supplementary service (SS-SD) at the Q reference point between Private Integrated services Network eXchanges (PINXs) connected together within a Private Integrated Services Network (PISN).

Supplementary service SD enables a user to communicate with another user or application by the exchange of keypad and display information transparently over a PISN. The Q reference point is defined in ISO/IEC 11579-1. Service specifications are produced in three stages and according to the method specified in ETS 300 387.

This International Standard contains the stage 3 specification for the Q reference point and satisfies the requirements identified by the stage 1 and stage 2 specifications in ISO/IEC 21407. The signalling protocol for SS-SD operates on top of the signalling protocol for basic circuit switched call control, as specified in ISO/IEC 11572, and uses certain aspects of the generic procedures for the control of supplementary services specified in ISO/IEC 11582.

This International Standard also specifies additional signalling protocol requirements for the support of interactions at the Q reference point between SS-SD and other supplementary services and ANFs. This International Standard is applicable to PINXs which can interconnect to form a PISN.