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 is used to transport INAP in Intelligent Networks and MAP in mobile phone networks.

TCAP messages are sent over the wire between machines. TCAP primitives are sent between the application and the local TCAP stack, all TCAP messages are primitives but there are primitives that are not messages, i.e. some are only transferred inside the local machine. A TCAP primitive is made up of one or more TCAP components.

A TCAP primitive may be one of the following types:

Invoke components have a signed 7 bit InvokeID which is present in all the other components to identify which invoke they relate to.

TCAP can be regarded as light weight implementation of the OSI defined ROSE, Remote Operations Services Element protocol

Transaction ID

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, the machine A sends a Begin message to machine B. This Begin message contains an Originating Transaction ID, which is the Transaction ID reference for A. When the 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 any of the machines 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

Invoke ID is a TCAP reference for a specific TCAP operation.

External links

* [http://www.itu.int/rec/T-REC-Q.773/en ITU-T Recommendation Q.773] : Transaction capabilities formats and encoding
* [http://www.itu.int/ITU-T/asn1/database/itu-t/q/q773/1997/ TCAP ASN1 specification]
* [http://www.iec.org/online/tutorials/ss7/ SS7 Tutorial] - SS7 tutorial, including TCAP description.