This Recommendation specifies: procedures for a single protocol for the transfer of data and control information from one session entity to a peer session entity; the means of selecting the functional units to be used by the session entities; the structure and encoding of the session protocol data units used for the transfer of data and control information; The procedures are defined in terms of: the interactions between peer session entities through the exchange of session protocol data units; the interactions between a session entity and the session service user in the same system through the exchange of session service primitives; the interactions between a session entity and the transport service provider through the exchange of transport service primitives.