TSAP (Transport Service Access Point) to mean a specific endpoint in the transport layer. The analogous endpoints in the network layer (i.e., network layer addresses) are not surprisingly called
NSAPs (Network Service Access Points). IP addresses are examples of NSAPs.
Application processes, both clients and servers, can attach themselves to a
local TSAP to establish a connection to a remote TSAP. These connections run through NSAPs on each host. The purpose of having
TSAPs is that in some networks, each computer has a
single NSAP, so some way is needed to distinguish multiple transport endpoints that share that
NSAP.
