> For the complete documentation index, see [llms.txt](https://prosbcdocs.telcobridges.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prosbcdocs.telcobridges.com/telecom-references/ss7-and-signalling/tcap/message.md). # Message A [TCAP](/telecom-references/ss7-and-signalling/tcap.md) message consists of three portions: the transaction portion (which contains the message type and parameters), the dialogue portion (which contains the application context name), and the component portion. ### Transaction portion These types of messages can be received or transmitted by the transaction portion of TCAP across the [SCCP](/telecom-references/ss7-and-signalling/sccp.md) transport service: **ITU, ETSI** * Unidirectional * Begin * Continue * End * Abort **ANSI** * Unidirectional * Query with permission * Query without permission * Conversation with permission * Conversation without permission * Response * Abort All TCAP messages except unidirectional message are implied for structured dialogue. Unidirectional message is implied for unstructured dialogue. ### Dialogue portion The dialogue portion is optional in a TCAP message and can only be present in 1992, 1996 ITU TCAP, 1996 ETSI TCAP, and 1996 ANSI TCAP messages. The dialogue portion is used to exchange the application context name and user-specific information. ### Component portion The component portion is mandatory in 1988 ITU TCAP, and 1988, 1992 ANSI TCAP messages, and is optional in other supported versions of TCAP. The following protocol data units (PDUs) can be received or transmitted in the component portion of a TCAP message: **ITU, ETSI** * Invoke * Return result not last * Return result last * Return error * Reject **ANSI** * Invoke not last * Invoke last * Return result not last * Return result last * Return error * Reject --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://prosbcdocs.telcobridges.com/telecom-references/ss7-and-signalling/tcap/message.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.