Introduction

The Transaction Capabilities Application Part (TCAP) is a SS7 application protocol that is used by a variety of distributed applications. TCAP provides non-circuit related information transfer capabilities and generic services to applications, yet TCAP remains independent of the application. Figure 7.1 shows how TCAP maps into layer 7 of the OSI model.

Figure 7.1: TCAP in the SS7 Layers

Application process services (such as 800 or Freephone services or networking ) use TCAP to provide enhanced network services and operations administration and maintenance (OAM) functions. An application process requiring serviced from TCAP is called a Transaction Capabilities User or TC-User. TCAP services may be used between:

• Signaling points;

• Signaling points and network service centers (such as databases or an OAM center),

• Network service centers.

TCAP itself does not provide any services to telecommunications network users. Instead, it provides the capability for a large variety of distributed applications to invoke procedures at remote locations on the SS7 network. A common procedure is the query of a Service Control Point (SCP) database.

For example, 800 or Freephone service uses the TCAP protocol to pass the dialed 800 numbers to an SCP database and request a translation to a routing number. The routing number is then returned to the signaling point to allow call routing.

TCAP services are based on a connectionless network service. Currently, no services are provided from the session, presentation or transport layers. TCAP interfaces directly with the SCCP, making use of the SCCP connectionless service to transfer...