For a protocol to support the CONS, there must be a mapping between the abstract primitives and parameters of the CONS and the real elements of the protocol. For the X.25 Packet Layer Protocol (PLP), the main body of this standard provides such a mapping for the X.25/PLP-1984 using Virtual Calls. Also provides a mapping of the CONS primitives and parameters to the X.25/PLP-1980 plus an SNDCP. These mappings apply to the X.25 VC service. Specifies two sets of procedures from which three classes of implementation are described.