TCAP provides the transaction capabilities carried out by non-circuit based messages used to access remote databases and invoke remote feature capabilities in network elements.

TCAP was first used for 800-number translation. TCAP messages carry the instructions SCPs use to query databases for specific information. TCAP also provides the mechanism to carry the queries and responses from switch to switch. TCAP uses SCCP and MTP protocols to route messages end-to-end. This is different from ISUP, which passes messages from switch to switch. The TCAP protocol provides the means for an application in one signaling point to communicate to an application in another signaling point.

The database information is used for 800, 888, and 900 service, Local Number Portability (LNP), subscriber service such as LIDB, and Mobile Home/Visitor records.

The Intelligent Network (IN) also uses TCAP to invoke features in remote end offices. IN relies on TCAP's services to enable one signaling endpoint to access features in a remote signaling endpoint. IN features such as automatic callback are made possible by TCAP invoke messages that inform the local exchange that the destination party is now available.

The following sections analyze TCAP interfaces, messages, message types, and components. The end of this chapter includes an example of an 800 query using the TCAP protocol.

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