Re: [pntaw] Real-time media over TCP

Michael Tuexen <Michael.Tuexen@lurchi.franken.de> Tue, 08 October 2013 12:39 UTC

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From: Michael Tuexen <Michael.Tuexen@lurchi.franken.de>
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Date: Tue, 8 Oct 2013 14:38:48 +0200
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To: Harald Alvestrand <harald@alvestrand.no>
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Cc: Bernard Aboba <bernard_aboba@hotmail.com>, "pntaw@ietf.org" <pntaw@ietf.org>, Parthasarathi R <partha@parthasarathi.co.in>, Dan Wing <dwing@cisco.com>
Subject: Re: [pntaw] Real-time media over TCP
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On Oct 8, 2013, at 6:09 AM, Harald Alvestrand <harald@alvestrand.no> wrote:

> 
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> On 10/07/2013 10:14 PM, Michael Tuexen wrote:
>> On Oct 7, 2013, at 10:08 PM, Dan Wing <dwing@cisco.com> wrote:
>> 
>>> 
>>> On Oct 7, 2013, at 11:32 AM, Bernard Aboba
> <bernard_aboba@hotmail.com> wrote:
>>> 
>>>> As you point out, in most cases ICE-TCP will not avoid use of TURN,
> so we are only talking about a modest efficiency gain for ICE-TCP and
> RTP over TCP, but a substantial increase in complexity.
>>>> 
>>>> Running SCTP over TCP is undesirable because the congestion control
> in SCTP and TCP will interact poorly with each other. 
>>> 
>>> And, even if a full SCTP stack is run over a full TCP stack, that
> will work but I agree won't work well.  But working is better than not
> working in situations where UDP is blocked.
>>> 
>>> To work well, we might look at SCTP Minion
> (draft-iyengar-minion-concept, which disables TCP's congestion control
> in lieu of SCTP's congestion control) is one answer to those conflicting
> congestion controls.
>> This would either require changing the TCP stack in the kernel or using a
>> userland TCP stack without CC, which would require using a raw socket for
>> sending, for receiving some other strategy, both would require root
> privileges...
>> Or am I missing something?
> 
> If I remember the minion overview correctly, it will in fact work on an
> unmodified TCP stack, but if there are ioctls available to get frames
> out of order, it can work a good deal better.
> 
> But you should get Iengar himself to talk about it if it's of interest.
His point is that you can work with an unchanged stack, but don't
get any benefit. The point in the above is to use a TCP without CC,
which requires an end-host change. So it is not so easy to get rid
of the TCP CC when using a kernel TCP stack.

Best regards
Michael
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