This Recommendation | International Standard specifies: a) procedures for the transfer of information among application-service-objects (ASOs); and b) the abstract and concrete syntax for the representation of the A-UNIT-DATA ACSE APDU. The A-UNIT-DATA procedure is defined in terms of: a) The interactions between peer ACSE protocol machines by the use of a supporting service; and b) the interaction between an ACSE protocol machine, its service-provider and its service-user. These procedures are applicable to instances of communication between systems which wish to communicate in an open systems interconnection environment in a connectionless mode. This Recommendation | International Standard also specifies conformance requirements for systems implementing this procedure. It does not contain tests which can be used to demonstrate conformance.