Session Initiation Protocol

Session Initiation Protocol or SIP for short is a signaling protocol used primarily for setting up communications within an IP network. SIP is an important component in the service that we offer; so important, in fact, that it’s in the name. After you read through these pages, you will know why we call our service OnSIP.

The Very Basics - What does SIP do?

The role of SIP within an IP communications network is to allow callers to easily locate their targeted recipients, and deliver session invitations effectively regardless of where the end users are located or what devices they are using. Its purpose is actually quite simple, but characteristics of the technology make SIP particularly powerful when used in conjunction with other protocols. Currently, SIP is the de facto standard protocol for establishing, manipulating and terminating VoIP communication sessions.

SIP excels in situations that require the following:

  • Locating and getting in touch with call participants, even as they switch locations or end user devices
  • Establishing communication sessions which involve various media types such as audio, video, or collaborative multimedia
  • Dealing with calls involving multiple participants that can hop in or out of the conversation

These scenarios reflect the several basic functions of SIP:

  • Locating users by translating their current network addresses from their SIP address
  • Adding, transferring, or dropping participants
  • Negotiating features so that participants in the session can agree on what will be supported among them
  • Allowing for changes in features in an ongoing session
For more technical info on SIP, here are the strict guidelines we follow as outlined in RFC 3261 by the IETF.