Defines in an abstract way the externally visible service provided by the OSI presentation layer in terms of the primitive actions and events at the user/service boundary, the parameter data associated with each primitive action and event, the relationship between, and the valid sequences of, those actions and events. The service defined is the connection-oriented service which is provided by the OSI connection-oriented presentation protocol and the connectionless service which is provided by the OSI connectionless presentation protocol, each in conjunction with the OSI session service.