Re: [Dart] multiplexing different media types (was: Commentary on draft-york-00)

"Paul E. Jones" <> Sun, 15 June 2014 04:52 UTC

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From: "Paul E. Jones" <>
To: Harald Alvestrand <>,
Date: Sun, 15 Jun 2014 04:52:38 +0000
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Subject: Re: [Dart] multiplexing different media types (was: Commentary on draft-york-00)
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>"SCTP ... can be multiplexed with one or more RTP sessions". Actually 
>we can only multiplex SCTP with a single RTP session. There have been 
>proposals that would allow multiplexing of multiple RTP sessions (each 
>containing multiple media flows) over a single 5-tuple, but these were 
>not accepted.

Your draft (draft-ietf-rtcweb-transports) says:

     RTCWEB implementations MUST support multiplexing of DTLS and RTP 
     the same port pair, as described in the DTLS_SRTP specification
     [RFC5764], section 5.1.2. All application layer protocol payloads
     over this DTLS connection are SCTP packets.

I had a question about this as we discussed the DART draft.  I assumed 
the only DTLS connection would be one used for key negotiation for SRTP. 
  Is that not the case? Would there be multiple DTLS connections 
multiplexed?  If so, how would one be differentiated from another?

As for RTP Session multiplexing, it's interesting to hear that proposals 
are dead.  Is there a proposal for multiplexing different media types 
(e.g., audio and video) within the same RTP Session, then?  RFC 3550 
discourages that, but it was my understanding that browser makers wanted 
to multiplex the different media types somehow.  What's the plan?