Transaction Capabilities Application Part

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. TCAP uses ASN.1 BER encoding, as well as the protocols it encapsulates, namely MAP in mobile phone networks or INAP in Intelligent Networks.

The transaction ID is a TCAP reference for a set of TCAP operations that are performed within a single dialog. When machine A starts a TCAP dialog with another machine B, A sends a Begin message to B. This Begin message contains an Originating Transaction ID, which is the Transaction ID reference for A. When machine B replies to A with a Continue message, it includes A's Transaction ID as the Destination Transaction ID. Furthermore, B includes its own Transaction ID as the Originating Transaction ID. As the TCAP dialog goes on, each Continue message includes the Transaction ID of the destination machine as the Destination Transaction ID and the Transaction ID of the originating machine as the Originating Transaction ID. When either machine wants to close the dialog, it sends an End message or an Abort message to the other machine. This message contains the Destination Transaction ID only.

Invoke ID is a TCAP reference for a specific TCAP operation and must be unique within a dialog.