Transport Services Access Point (TSAP)
A Transport Services Access Point (TSAP) is an end-point for communication between the Transport layer (layer 4) and the Session layer in the OSI (Open Systems Interconnection) reference model. Each TSAP is an address that uniquely identifies a specific instantiation of a service. TSAPs are created by concatenating the node's Network Service Access Point (NSAP) with a transport identifier, and sometimes a packet and/or protocol type.