This International Standard specifies the signalling protocol for the support of the Private User Mobility Registration supplementary service (SS-PUMR) at the Q reference point between Private Integrated services Network eXchanges (PINXs) connected together within a Private Integrated Services Network (PISN). SS-PUMR is a supplementary service which enables a PUM user to register at, or de-register from, any wired or wireless terminal within the PISN. The ability to register at different locations in the PISN at different times enables the PUM user to maintain the provided services (including the ability to make and receive calls) at different access points. De-registration is used to inform the PISN that the PUM user is temporarily unable to make use of the provided services (including the receipt of calls). SS-PUMR may provide the PUM user with the ability to obtain information on the current registration sessions (interrogation). 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 ITU-T Rec 1.130. 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 17875. The signalling protocol for SS-PUMR 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-PUMR and other supplementary services and ANFs. NOTE 1 — 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 interconnect to form a PISN. This International Standard applies to PUM only within a single PISN.