Defines the OSI network service in terms of the primitive actions and events, the parameters associated with them, the interrelationship between, and the valid sequences of, these actions and events. The principal objectives are to specify the characteristics of a conceptual network service, to encourage convergence of the capabilities offered by providers of subnetworks, to provide a basis for the individual enhancement of existing heterogeneous subnetworks to a common subnetwork-independent network service, to provide a basis for the development and implementation of subnetwork-independent transport layer protocols.