This International Standard defines the mapping functions in exchanges of private integrated services networks (PISN) required for their attachment to Virtual Private Network (VPN) functionality of public (or third party provided) network equipment. Mapping functions are required to provide for the physical termination of the interface at the C or T reference points, and for the mapping of user channels and signalling information flows at the Q reference point to the appropriate channels or time-slots at the C or T reference point. At the T reference, point it is assumed that the protocol used on the D channel is the enhanced version of DSS1. These protocol enhancements are given in Annex Q and Annex X of Recommendations Q.931 and Q.932 respectively. The mapping function specified in this International Standard are applicable to PINXs connected to a VPN that supports either PISN information flows between accesses and/or PISN services. The C and Q reference points are defined in ISO/IEC 11579-1. The T reference point is defined in ITU-T Rec. I.411. The types of interfaces at the C or T reference point covered by this International Standard are the ISDN primary rate interface and the basic access interface.