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For better understanding of this chapter please read ITU-T Q.771 to Q.774.
TCAP supports the exchange of non-circuit related data between applications across the SS7 network using the SCCP connectionless service. Queries and responses sent between SSPs and SCPs are carried in TCAP messages. For example, an SSP sends a TCAP query to determine the routing number associated with a dialed 800/888 number and to check the personal identification number (PIN) of a calling card user. In mobile networks (IS-41 and GSM), TCAP carries Mobile Application Part (MAP) messages sent between mobile switches and databases to support user authentication, equipment identification, and roaming.
TCAP messages and parameters are refered as primitives
. Primitives are exchanged
within logical entity called dialog. There are two types of dialogs:
Unstructured - short lived, it is created only to deliver single message (Unstructured primitive
), after delivery dialog is invalidated.
Structured - long lived, it is created when exchange starts and lives until it is terminated.
TCAP defines following message types:
Unstructured - creates Unstructured dialog. Unstructured dialog is invalidated once this message is either sent or consumed. It is meant for messages which dont require answer or interaction.
Begin - message sent to begin Structured dialog, it carries context information for dialog being created
Continue - continues Structured dialog
End - ends Structured dialog in graceful way
Abort - aborts Structured dialog
TCAP messages convey two types of information:
components - elements which carry information on requested operation, their status and result.
dialog related - dialog context(application context name) and application specific information(user information)