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Receiving SIP from Twilio


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"?>

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.

You can receive a UUI (User-to-User) header through a webhook as a parameter for incoming calls to Twilio. UUI header will be prepended with SipHeader_ prefix in request parameters. For example, SipHeader_User-to-User "123456789;encoding=hex".

The region parameter

To specify the geographic region from which Twilio will send SIP-out traffic towards your communication infrastructure, you must include the region parameter in your SIP URI. For example, if the region=ie1 parameter is included in your SIP URI, Twilio will send the SIP traffic from the Europe Ireland region:

<?xml version="1.0" encoding="UTF-8"?>
Region Location
us1 North America Virginia
us2 North America Oregon
ie1 Europe Ireland
de1 Europe Frankfurt
sg1 Asia Pacific Singapore
jp1 Asia Pacific Tokyo
br1 South America São Paulo
au1 Asia Pacific Sydney

If the region parameter is not specified, Twilio will send SIP-out traffic from the North America Virginia region.


  • You must make sure you whitelist the IP addresses of the Twilio region for SIP signaling and RTP media traffic.
  • The region parameter is not supported when calling SIP registered endpoints, the parameter will be ignored if present. SIP-out traffic will always be sent from the Twilio region the SIP endpoint registered with.
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