This International Standard specifies the supplementary service Simple Dialog (SS-SD), which is applicable to various basic
services supported by Private Integrated Services Networks (PISNs). Basic services are specified in ISO/IEC 11574.
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.
Service specifications are produced in three stages, according to the method described in ETS 300 387. This International
Standard contains the stage 1 and stage 2 specifications of SS-SD. The stage 1 specification (clause 6) specifies the
supplementary service as seen by users of PISNs. The stage 2 specification (clause 7) specifies the functional entities involved
in the supplementary service and the information flows between them.