The ACSE supports two modes of communication: connection-oriented and connectionless. The ACSE Service Definition (see ITU-T Rec. X.217 | ISO/IEC 8649) includes both modes of communication. This Recommendation | International Standard provides the protocol specification of the connectionless mode of communication. The protocol specification for the connection-oriented mode of communication is contained in ITU-T Rec. X.227 | ISO/IEC 8650-1.

This Protocol Specification specifies:

• procedures for the transfer of information, between application-entities; and
• the abstract syntax for the representation of the A-UNIT-DATA ACSE APDU.

The A-UNIT-DATA procedure is defined in terms of:

• the interactions between peer ACSE protocol machines by the use of connectionless presentation-service; and
• the interaction between an ACSE protocol machine 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 Protocol Specification also specifies conformance requirements for systems implementing this procedure. It does not contain tests which can be used to demonstrate conformance.