The OSI CONS, as stated above, is defined in terms of a set of primitive actions and events and associated parameters. For a protocol to support this service, there must be a mapping between the abstract primitives and parameters of the CONS and the real elements of the protocol. This International Standard provides such a mapping for the X.25/PLP-1984. It also provides a mapping of the CONS primitives and parameters to the X.25/PLP-1980 plus an SNDCP (Annex A). In addition, the method of selecting the appropriate mapping, if any, for different combinations of end systems and Network Layer relay systems implementing one or more of the mappings is defined (Annex B).
This International Standard specifies the conformance requirements for three classes of implementation. These requirements are applicable both to end system operation and to half the operation of a Network Layer relay. Where relay operation is concerned, the two halves of the relay may be the same or different classes of implementation.
This International Standard specifies the requirements to be met by a Conforming-1984 implementation. Implementations in this dass are designed to operate directly and efficiently with other Conforming-1984 implementations, including cases of operation across an X.25(1984) subnetwork.
This International Standard also specifies the requirements to be met by a Conforming-1980 implementation. Implementations in this dass are designed to operate directly with other Conforming-1980 implementations, including cases of operation across any form of X.25 subnetwork, but will operate less efficiently than Conforming-1984 implementations.
This International Standard also specifies the requirements to be met by a Compatible implementation. Implementations in this dass are designed to operate directly with all other implementation classes, including cases of operation across any type of X.25 subnetwork. They make efficient use of X.25(1984) when placed in this environment.