This Recommendation I International Standard defines in an abstract way the externally visible service provided by the OSI Transport Layer in terms of:
a) the primitive actions and events of the service;
b) the parameter data associated with each primitive action and event;
c) the relationship between, and the valid sequences of, these actions and events.
The service defined in this Recommendation I International Standard is that which is provided by all OSI Transport Protocols (in conjunction with the Network Service) and which may be used by any OSI Session Protocol.
This Recommendation I International Standard does not specify individual implementations or products, nor does it constrain the implementation of entities and interfaces within a system. Conformance of equipment to this Recommendation I International Standard is achieved by conformance to the protocols specified to fulfil the Transport Service defined in this Recommendation I International Standard.