SS-RE is a supplementary service which provides for the redirection of a call transferred by the served user back to the served user if the call is unanswered. SS-RE is only applicable after transfer by join, not after transfer by rerouteing.
Service specifications are produced in three stages, according to the method described in ETS 300 387. ISO/IEC 15051:2003 contains the stage 1 and stage 2 specifications of SS-RE. The stage 1 specification (clause 6) specifies the supplementary service as seen by users of PISNs. The stage 2 specification (clause 7) identifies the functional entities involved in the supplementary service and the information flows between them.