Defines the OSI Network Service in terms of (a) the primitive actions and events of the Service, (b) the parameters associated with each primitive action and event, and the form which they take, and (c) the inter-relationship between, and the valid sequences of, these actions and events. The Standard is published with an addendum which provides a description of a connectionless-mode service and of functions related to it, which may be provided by the Network Layer of the OSI Reference Model. The addendum adds to the concepts and principles defined in the Standard, without modifying them. Identical with ISO 8348 and ISO 8348/Add 1.