# SIP

## Session Initiation Protocol

Session Initiation Protocol ([SIP](/docs/glossary/what-is-session-initiation-protocol-sip)) is a signaling protocol for initiating, terminating and modifying user sessions over an IP network.

### [How Twilio Uses SIP](/docs/glossary/what-is-session-initiation-protocol-sip#how-twilio-uses-sip)

[Using SIP to connect to Twilio is one way](https://www.twilio.com/en-us/voice/sip-interface) to get access to Twilio's global reach and powerful automation and scripting functions.

You can connect your on-site or virtual Private Branch Exchange (PBX) with Twilio's servers. Here's our overview of [connecting your existing SIP communications](/docs/voice/api/sending-sip) infrastructure to us.

> \[!NOTE]
>
> For information about SIP Trunking with Twilio, check out our [Elastic SIP Trunking documentation](/docs/sip-trunking).

Dig into our [API Reference docs for Twilio's SIP Domains](/docs/voice/sip/api):

* [SIP Credential Resource](/docs/voice/sip/api/sip-credential-resource)
* [SIP CredentialList](/docs/voice/sip/api/sip-credentiallist-resource)[Resource](/docs/voice/sip/api/sip-credentiallist-resource)
* [SIP CredentialListMapping](/docs/voice/sip/api/sip-credentiallistmapping-resource)[Resource](/docs/voice/sip/api/sip-credentiallistmapping-resource)
* [SIP Domain](/docs/voice/sip/api/sip-domain-resource)[Resource](/docs/voice/sip/api/sip-domain-resource)
* [SIP IpAccessControlList Resource](/docs/voice/sip/api/sip-ipaccesscontrollist-resource)
* [SIP IpAccessControlListMapping Resource](/docs/voice/sip/api/sip-ipaccesscontrollistmapping-resource)
* [SIP IpAddress Resource](/docs/voice/sip/api/sip-ipaddress-resource)