This Recommendation | International Standard defines in an abstract way the externally visible service provided by the OSI Session Layer in terms of the primitive actions and events of the service; the parameter data associated with each primitive action and event; the relationship between, and the valid sequence of these actions and events. The service defined in this Recommendation | International Standard is that which is provided by the OSI session protocol (in conjunction with the transport service) and which may be used by the OS1 presentation protocol. This Recommendation | International Standard does not specify individual implementations or products, nor does it constrain the implementation of entities and interfaces within a computer system. There is, therefore, no conformance to this Recommendation | International Standard. The text pertaining to the symmetric synchronization functional unit is not applicable to the support of ITU-T applications.