ISO/IEC 20113:2004 specifies supplementary service Make Call Request (SS-MCR), which is related, but not limited to, various basic services supported by Private Integrated Services Networks (PISNs). Basic services are specified in ISO/IEC 11574.

The supplementary service MCR enables a Requesting User to request a Co-operating User to establish a new Requested Call to a Destination User. This new Requested Call between the Co-operating and Destination User can be either a Basic call or call independent signalling connection.

Service specifications are produced in three stages, according to the method described in ETS 300 387. ISO/IEC 20113:2004 contains the stage 1 and stage 2 specifications of SS-MCR. The stage 1 specification specifies the supplementary service as seen by users of PISNs. The stage 2 specification specifies the functional entities involved in the supplementary service and the information flows between them.