Transaction Capabilities Application Part, from ITU-T recommendations Q.771-Q.775 or ANSI T1.114 is a protocol for Signalling System 7 networks.
Its primary purpose is to facilitate multiple concurrent dialogs between the same sub-systems on the same machines, using Transaction IDs to differentiate these, similar to the way TCP ports facilitate multiplexing connections between the same IP addresses on the Internet.
End and Abort primitives only have a Destination Transaction ID.
The component portion for the unidirectional primitive is mandatory.
TCAP is based on the OSI defined ROSE, Remote Operations Services Element protocol.