Websockets and SIP

Yesterday, RFC 6455 The Websocket Protocol was published by the IETF. This is the latest standard in the efforts to enable more applications to run in the web browser. This protocol, when supported in a browser and webserver allows the two to open additional TCP connections between them, besides the one they are using for the web session to send HTML, JavaScript, etc to the browser.

One area of application is WebRTC, the work to enable real-time communications services in web pages. One approach that has been discussed in both the IETF and W3C is to use Websockets to open a new connection between the browser and web server, and run a signaling, presence, or instant messaging protocol over it. For example, it had been proposed to run SIP, Session Initiation Protocol, this way.

A few months ago I blogged about WebRTC and SIP, and argued that SIP should not be standardized by WebRTC, as had been proposed back then. I still believe this is correct, and recent work in the IETF has centered around instead standardizing some kind of offer/answer media negotiating protocol, but leave the choice of signaling protocol open.

Recently a new Internet Draft was submitted on a Websocket transport for Session Initiation Protocol. I think this is a potentially useful approach and could be a good way to utilize SIP in conjunction with WebRTC. The draft is still in it’s early days, and has not yet been adopted by the SIPCORE Working Group yet, but I think it is a great start. SIP developers who are interested in the WebRTC effort should read this draft and support this work.

In the meantime, it is great to see WebSocket finally published as an RFC, something I hope to see happen to a few of my Internet Drafts in the new year!


If you are interested in WebRTC, you might like my new book “WebRTC: PIs and RTCWEB Protocols of the HTML5 Real-Time Web”

WebRTC: APIs and RTCWEB Protocols of the HTML5 Real-Time Web Book Cover


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  1. #1 by Iñaki Baz Castillo on December 12, 2011 - 4:43 pm

    Hi, the draft “SIP over WebSocket” has a new name (now “draft-ibc-sipcore-sip-websocket” since it no longer belongs to RTCWEB WG) and has been already introduced into SIPCORE WG:



    • #2 by Alan B. Johnston on December 12, 2011 - 5:00 pm

      Hi Iñaki, my apologies for linking to the old version of the draft. I have updated the link to draft-ibc-sipcore-websocket-00, where it is currently under discussion in the SIPCORE WG.

      • #3 by Iñaki Baz Castillo on December 12, 2011 - 9:55 pm

        Thanks a lot Alan. If you consider it interesting for your post, a friend of mine and me have a web page with a presentation of this technology (SIP over WebSocket) along with a real demo of a SIP proxy implementing the WebSocket transport and a JavaScript SIP library doing the same (it includes a real video):


        Best regards.

  2. #4 by Ravin Dimantha on January 26, 2012 - 8:00 am

    Hi Iñaki that is a very impressive demo! When can we test out this client? Will you release it as Open Source?

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