This International Standard specifies the mapping functions for a pair of on-demand inter-PINX connections using a circuit mode basic service and the supplementary service User-to-User Signalling (service 3) of a public ISDN at the same time. In order to connect a Private Integrated Services Network Exchange (PINX) to another PINX, mapping functions are required to adapt the specific interfaces at the C reference point to the application at the Q reference point. As such, mapping functions provide for physical adaptation to the interface at the C reference point. Mapping functions also provide for the mapping of user channels and signalling information at the Q reference point to the appropriate channels or timeslots at the C reference point. The C and Q reference points are defined in ISO/IEC 11579-1. At the Q reference point the mappings provide a 64 kbit/s service for user channels and a packet mode service for the signalling channel. Bearer conditioning is outside the scope of this International Standard, except for providing the layer 2 for the signalling channel at the Q reference point. Scenario management is outside the scope of this International Standard. This International Standard is applicable to PINXs which can be interconnected to form a Private Integrated Services Network (PISN) and which support signalling protocols at the Q reference point.