Re: [rtcweb] SCTP for data channels in rtcweb

Randell Jesup <randell-ietf@jesup.org> Thu, 22 September 2011 16:46 UTC

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Date: Thu, 22 Sep 2011 12:45:41 -0400
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Subject: Re: [rtcweb] SCTP for data channels in rtcweb
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On 9/22/2011 11:27 AM, Randell Jesup wrote:
> On 9/22/2011 3:53 AM, Randell Jesup wrote:
>> On 9/21/2011 7:45 AM, Hadriel Kaplan wrote:
>>> Just to make sure I'm on the same wavelength, you're talking about:
>>> 1) Defining PseudoTCP over UDP (a la libnice and jingle) for 
>>> stream-oriented reliable data delivery.
>>
>> I would also consider SCTP-over-UDP in place of PseudoTCP-over-UDP 
>> for reliable
>> data delivery.  Similar arguments apply as for DCCP (solid 
>> specification), and
>> in addition the FreeBSD implementation apparently supports 
>> SCTP-over-UDP and is
>> very portable, so good working code is available to start.  SCTP also 
>> has other
>> benefits, like optional out-of-order delivery, and a datagram 
>> ('message') orientation.
>
> I'm in touch with the SCTP-over-UDP draft authors, and received this:
>
>     so you want a reliable and unreliable datagram service. You can use SCTP for both:
>     1. Standard SCTP/UDP for a reliable datagram service.
>     2. SCTP/UDP with the PR-SCTP extension and using a policy which doesn't do
>         retransmissions. This is also implemented in the FreeBSD implementation
>         and the derived ones, like the one for Mac OS X, Userspace and so on.
>
>     There is also an RFC for running DTLS/SCTP which also applies to DTLS/SCTP/UDP
>     to secure the traffic. We also have running code for it as you can get a
>     patch for OpenSSL from
>     http://sctp.fh-muenster.de/dtls-patches.html
>     It has been submitted to the OpenSSL maintainers for inclusion in OpenSSL 1.0.1.
>
>     Please let us know if you have any further question.
>
> So, overall this seems *very* promising - both in terms of a single framework to use
> for all the data channels (one interface/API, etc), existing congestion control
> (unfortunately TCP-like -- loss-based -- but oh well), and a working, open
> -over-UDP/-over-DTLS spec and implementation.

They also inform me that there are alternative CC implementations in the 
BSD code, and the CC code it replaceable/overridable, so even better.

> I'd still love to tie the congestion control into the unified control we're looking
> at for the media streams, but I think we can make this work well even without that.
>
>
> -- 
> Randell Jesup
> randell-ietf@jesup.org
>
>
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-- 
Randell Jesup
randell-ietf@jesup.org