Re: [MMUSIC] SCTP question: Where does it multiplex?

Paul Kyzivat <> Mon, 03 December 2012 19:36 UTC

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Date: Mon, 03 Dec 2012 14:36:18 -0500
From: Paul Kyzivat <>
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Subject: Re: [MMUSIC] SCTP question: Where does it multiplex?
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On 12/3/12 2:53 AM, Harald Alvestrand wrote:
> On 12/01/2012 07:09 PM, Paul Kyzivat wrote:
>> I must say that I am getting confused about what is being multiplexed
>> here. We must be very careful to be precise.
>> SCTP defines an *association*, which in simple cases is bound to a
>> 5-tuple. (For now lets not talk about the cases where each end can
>> have more than one address.)
>> SCTP multiplexes multiple one-way *streams* over an association.
>> (These are not RTP streams.)
>> RTCWEB binds pairs of sctp-streams together into *channels*.
> I'm not talking about any of these levels. I'm talking about the reuse
> of the RTP session's 5-tuple for the DTLS/SRTP 5-tuple, as described in
> RFC 5764 section 5.1.2.

These are all related. We are making even more of a mess of SDP than it 
already is by patching on a new hack for each sort of multiplexing 
somebody comes up with. But focusing on just this:

How do you imagine this multiplexing will be signaled in SDP?
The obvious way would be to bundle the DTLS/SCTP m-line with the RTP 
m-lines. But that will violate the rule that all the bundled m-lines 
have the same <proto>. (And there is an even worst fit between this and