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

"Dan Wing" <> Tue, 11 December 2012 18:53 UTC

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Date: Tue, 11 Dec 2012 10:53:30 -0800
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Subject: Re: [MMUSIC] SCTP question: Where does it multiplex?
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> -----Original Message-----
> From: [] On Behalf
> Of
> Sent: Tuesday, December 11, 2012 2:34 AM
> To:;
> Cc:
> Subject: Re: [MMUSIC] SCTP question: Where does it multiplex?
> Hi Sal,
> Salvatore Loreto wrote:
> >
> >based on the current stack the SCTP traffic is the only traffic that
> >runs directly over the DTLS stack.
> >What I am trying to do is to include the Randell Jesup (I am including
> >him in CC as I am not sure he is subscribed to this mailing list)
> >  suggestion to give the possibility to have multiple SCTP
> >*associations* running  on top of the same DTLS session and of course
> >providing a way to signal it in SDP.
> >
> >to be clear: at moment WebRTC allows only one SCTP association per PC,
> >so this is something that would be nice to define just to be ready for
> the future.
> >
> It's a bit unclear to me what the benefit of this would be. SCTP itself
> allows multiple streams to be transported in parallel within a single
> SCTP association. So, in what type of situations would we need multiple
> parallel SCTP associations? I thought the main point of SCTP is that it
> provides the parallelism and multiplexing by itself.
> In other words: I do understand the desire to multiplex RTP and SCTP
> within the same UDP flow, so we can for instance reduce the number of
> needed NAT/FW bindings.

Sending bulk data (SCTP) and interactive audio/video over the same port
will break prioritization of the audio/video flow above the bulk data.

> I also understand why multiple independent non-
> HOL blocking streams within SCTP are useful for applications. But I
> don't yet understand the additional benefit of multiple parallel SCTP
> associations. No doubt it can be technically done, but to what purposes?

One example:  transferring a big file while, at the same time, doing 
screen sharing or an instant message chat.