This International Standard specifies the signalling protocol for the support of Recall supplementary service (SS-RE) at the Q reference point between Private Integrated services Network eXchanges (PINXs) connected together within Private Integrated Services Network (PISN). SS-RE is a supplementary service which provides for the re-direction of a transferred call back to the served user if the call is unanswered. SS-RE is only applicable after transfer by join, not after transfer by rerouteing. 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 15051. The signalling protocol for SS-RE 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-RE and other supplementary services and ANFs. However, the interaction with the Call Transfer supplementary service is specified as part of SS-RE signalling procedures as it is the essential aspect of the Recall supplementary service. NOTE — Additional interactions that have no impact on the signalling protocol at the Q reference point can be found in the relevant stage 1 specifications. This International Standard is applicable to PINXs which can be interconnected to form a PISN.