Re: [pntaw] Real-time media over TCP

Dan Wing <dwing@cisco.com> Tue, 08 October 2013 15:04 UTC

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From: Dan Wing <dwing@cisco.com>
In-Reply-To: <AC0ADD1C-C99C-4B62-BE0E-D52A2C7093A9@lurchi.franken.de>
Date: Tue, 8 Oct 2013 08:04:03 -0700
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References: <CAGTXFp92jSzQz05uHngzscz88n=fT_JPbEvQRxgeUUqPVRQUyQ@mail.gmail.com> <52244DD7.1020900@alvestrand.no> <BLU405-EAS183E36A927CA42270B6936D93300@phx.gbl> <522590EE.7070508@alvestrand.no> <C632A223-A55A-47F4-B083-9BDC447DA959@cisco.com> <52262657.3080208@alvestrand.no> <A2C315DB-1882-4BD1-A8C0-E8AF7DEA48F4@cisco.com> <00ca01cec387$f881cae0$e98560a0$@co.in> <BLU406-EAS274696C3D9DFE505F96B8E393130@phx.gbl> <2924C1EA-613D-4B05-BD24-4CFD1411386E@cisco.com> <28C05866-180F-41B2-8466-502F57FF1DF1@lurchi.franken.de> <5253857F.6010802@alvestrand.no> <AC0ADD1C-C99C-4B62-BE0E-D52A2C7093A9@lurchi.franken.de>
To: Michael Tuexen <Michael.Tuexen@lurchi.franken.de>
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Cc: Bernard Aboba <bernard_aboba@hotmail.com>, Harald Alvestrand <harald@alvestrand.no>, "pntaw@ietf.org" <pntaw@ietf.org>, Parthasarathi R <partha@parthasarathi.co.in>
Subject: Re: [pntaw] Real-time media over TCP
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On Oct 8, 2013, at 5:38 AM, Michael Tuexen <Michael.Tuexen@lurchi.franken.de>; wrote:

> On Oct 8, 2013, at 6:09 AM, Harald Alvestrand <harald@alvestrand.no>; wrote:
> 
>> 
>> -----BEGIN PGP SIGNED MESSAGE-----
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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 application sees SCTP -- that must have some benefit.

-d


> 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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>