Re: [rtcweb] DataChannel Questions

Eric Rescorla <> Mon, 22 July 2013 18:21 UTC

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From: Eric Rescorla <>
Date: Mon, 22 Jul 2013 11:20:14 -0700
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To: Roman Shpount <>
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Subject: Re: [rtcweb] DataChannel Questions
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On Mon, Jul 22, 2013 at 11:15 AM, Roman Shpount <> wrote:

> I am sorry if I missed this somewhere in the draft, but I got two
> DataChannel related questions:
> First question: is it possible to bundle DataChannel with DTLS-SRTP? I do
> not see how this can be implemented since DTLS in DataChannel can negotiate
> any encryption protocol and I do not see a simple way to de-mux this on the
> wire.

I don't understand that "negotiate any encryption protocol" means. The SCTP
in the
DataChannel is encrypted under DTLS. The only potential problem here could
demuxing the SCTP from non-SCTP traffic once you have demuxed DTLS versus
SRTP, but we don't support anything that's non-SCTP here yet.

> Just wanted to confirm that bundling is not something that is planned to
> be supported.

As far as I know, it's fine.

Second question: is there a way to time synchronize DataChannel messages
> and real time media? For instance I want to use DataChannel for a subtitle
> track, is there a way to synchronize messages with video track?

You would presumably need to add the timing data into the DC messages
themselves, since SCTP does not provide any real-time function.