Re: [rtcweb] Requesting "SDP or not SDP" debate to be re-opened

Matthew Jordan <> Tue, 18 June 2013 19:19 UTC

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Date: Tue, 18 Jun 2013 14:19:14 -0500
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Subject: Re: [rtcweb] Requesting "SDP or not SDP" debate to be re-opened
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On Tue, Jun 18, 2013 at 1:22 PM, Adrian Georgescu <>wrote;wrote:

> +1
> While working with the specs, some may have realised that SDP is not such
> a great idea to put in practice and may also want to come forward to admit
> their mistake.
> Regards,
> Adrian
In the Asterisk project, we were able to use our legacy SIP stack to enable
very basic WebRTC communication with Chrome and FireFox. That sounds nice,
until you realize we have to continually preface that with "sometimes".

Because the answer is, more often than not, something breaks. Invariably,
the breakages have been in the SDPs sent to Asterisk by the browser. What
SDP breaks us changes depending on the browser being used, the version of
said browser, and whether or not some new WebRTC SDP feature has been put
in the browser's latest release. And just when we think we have to modify
Asterisk to handle the new SDP sent by some browser, the browser changes
again. As a result, Asterisk 11 hasn't changed a lot since we released;
we've been trying to avoid coding to a moving target. We always envisioned
that things would quiet down and the browsers would settle on an
implementation of SDP that we could adapt to - but it doesn't seem like
things are quieting down as much as we'd like. And sure, the SIP stack in
Asterisk is crufty, and sure, sometimes the fault is in our implementation,
not the browser's - but I think we on the Asterisk project can certainly
say that relying on SDP hasn't been a panacea for interoperability.

It feels like maintaining compatibility with "traditional" SDP
implementations is getting harder for the browsers to manage and holding
the entire process back. As one of those older "traditional"
implementations, I'd rather write an entirely new channel driver for
Asterisk than have to re-write our SDP handling.

So... +1 to Inaki's request.


Matthew Jordan
Digium, Inc. | Engineering Manager
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
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