Chapter 10. Transaction Capabilities Application Part (TCAP)

The Transaction Capabilities Application Part (TCAP) of the SS7 protocol allows services at network nodes to communicate with each other using an agreed-upon set of data elements. Prior to SS7, one of the problems with implementing switching services beyond the boundary of the local switch was the proprietary nature of the switches. The voice circuits also had very little bandwidth for signaling, so there was no room for transferring the necessary data associated with those services. Moving to a Common Channel Signaling (CCS) system with dedicated signaling bandwidth allows the transfer of a greater amount of service-related information. Coupling the standardization of data communication elements with the necessary bandwidth to transmit those elements creates the proper foundation for a rich service environment. To that end, TCAP provides a generic interface between services that is based on the concept of "components." Components comprise the instructions that service applications exchange at different nodes.

This chapter examines components and other details of the TCAP protocol, including the following:

• Overview of TCAP

• Message types

• Transactions

• Components

• Dialogue portion

• Message encoding

• Element structure

• Error handling

• ITU protocol message contents

• ANSI protocol message contents

• ANSI national operations

In trying to understand how TCAP works, the differences between ANSI TCAP (as presented in the ANSI T1.114) and ITU TCAP (as presented in the Q.700 series) are normalized as much as possible. While differences between the two certainly exist, a great deal of commonality also exists and often varies only in the naming of identifiers.