This part of ISO/IEC 11579 specifies a reference configuration (RC) for the extension line of a private integrated services network exchange (PINX) including high level functions in addition to the physical termination system specified in part 1 of ISO/IEC 11579. Since such high level functions appear application dependent and can occur, in principle, in any multiplicity and combination, no firm allocation of functional groupings and thus no firm reference points can be indicated. Instead, the principles for combining functional groupings associated with the physical termination system and allocating reference points are specified in this part of ISO/IEC 11579. Examples for some combinations of functional groupings and the allocation of reference points are given in annex A. The principle is not intended to require any specific implementation of a PINX, but only to provide guidance for the specification of PINX capabilities. The principle is sufficient to support ISDN-like applications. It can be extended to also support non-ISDN-like applications.