> For the complete documentation index, see [llms.txt](https://docs.bird.com/connectivity-platform/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.bird.com/connectivity-platform/sip-trunking/what-is-a-sip-trunk.md). # What is a SIP Trunk? MessageBird SIP Trunking offers you the possibility to place outbound voice calls from your VoIP platform to phones anywhere in the world. A SIP-trunk makes calls via the public internet or a private IP-connection. Our SIP-trunks run authentication protocols on your IP-addresses and/or a username-password combination. You can learn how to set up accepting inbound SIP-calls with our [step-by-step guide.](/connectivity-platform/sip-trunking/sip-trunking.md) --- # 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 dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.bird.com/connectivity-platform/sip-trunking/what-is-a-sip-trunk.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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.