Receiving SIP from Twilio

Overview

Twilio’s Programmable Voice SIP product enables your advanced voice applications to initiate SIP sessions from the Twilio cloud towards your existing SIP communications infrastructure using TwiML and/or the REST APIs.

Programmable Voice SIP Diagram

How it works

With Programmable Voice SIP, there are a couple of ways to connect your Twilio application to your SIP communications infrastructure.

  1. Your application can use Twilio’s REST APIs to initiate a new SIP call towards your SIP communications infrastructure
  2. An inbound PSTN or SIP call can invoke your application which can respond using the <Sip> noun of the <Dial> verb, to establish a call with your SIP endpoint.
<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <Dial>
    <Sip>sip:jack@example.com</Sip>
  </Dial>
</Response>

Getting Started

To start receiving SIP from Twilio towards your communications infrastructure, there is one major step you need to follow:

Whitelist Twilio’s SIP IP addresses and media ports in your system

To ensure that your communications infrastructure doesn’t block communication, you must update your whitelist. See here for details.

Now that Twilio’s IPs are whitelisted in your system, your Twilio app can begin sending SIP traffic to your SIP communications infrastructure. If you are new to Twilio, it’s best to start out with <Sip> noun of the <Dial> for your first app. See here for details.

Advanced Features

SIP X-Headers

The following headers will always be added by Twilio to the outgoing initial INVITE request. You may optionally use these fields in your communications infrastructure.

  • X-Twilio-CallSid: A unique identifier for this call, generated by Twilio. It is 34 characters long, and always starts with the letters CA.
  • X-Twilio-AccountSid: Your Twilio account SID. It is 34 characters long, and always starts with the letters AC.
  • X-Twilio-ApiVersion: The Twilio API version being used for this call session.