Overview

* Session Initiation Protocol (SIP) is a signalling protocol for initiating, terminating, and modifying user sessions over an IP network

• Most commonly, SIP is used for Voice Over IP (VoIP) services, but is also often used for other communications sessions such as video calls and instant messaging sessions

SIP Endpoints are called User Agents

• By mapping SIP endpoints (user agents, in SIP terminology) to Uniform Resource Identifiers (URIs), SIP is quite similar to the HTTP model of requests and responses.
• Unlike HTTP, SIP can use UDP or other transport types
• SIP is a text-based protocol and uses UTF-8 encoding

SIP Trunking

* A SIP trunk is the virtual version of an analog phone line

• Using SIP trunks, a SIP provider can connect 1, 2, or 20 channels to your PBX, allowing you to make local, long distance, and international calls over the Internet.
  • If you have an on-premises PBX in your office, a SIP trunk provider can connect to you and allow you to make outbound calls on your existing system, without restrictions on the number of concurrent calls

Twilio’s usage

Using SIP to connect to Twilio is one way to get access to Twilio’s global reach and powerful automation and scripting functions.

It’s easy to connect your on-site or virtual Private Branch Exchange (PBX) with Twilio’s servers. Here’s our overview of connecting your existing SIP communications infrastructure to us.