Specifies procedures for a single protocol for the transfer of data and control information from one session entity to a peer session entity; the means of selecting the functional units to be used by the session entities; and the structure and encoding of the session protocol data units used for the transfer of data and control information. These procedures are applicable to instances of communication between systems which support the Session Layer of the OSI Reference Model and which wish to interconnect in an open system environment. This Standard also specifies conformance requirements for systems implementing these procedures. This Standard is identical with ISO 8327:1987.