Re: [tcpm] [Tmrg] Increasing the Initial Window - Notes

[Yuchung Cheng <[e-mail]>]

On Tue, Nov 16, 2010 at 6:09 AM, Fred Baker <[e-mail]> wrote:

>
> On Nov 16, 2010, at 10:01 PM, Ilpo Järvinen wrote:
>
> > On Tue, 16 Nov 2010, Fred Baker wrote:
> >
> >> On Nov 11, 2010, at 7:48 AM, Jerry Chu wrote:
> >>
> >>> I wonder what factors will argue that the initial quantum can't be
> changed?
> >>> Someone has argued in the past IW10 effectively "disable CC algorithm".
> >>> But haven't we already done that years ago when moving up IW from 1 to
> 3 if
> >>> one insisted then that the initial quantum must be 1?
> >>
> >> Actually, no. I may be the person who said that this effectively
> >> disables congestion control in the average case; my reason for saying
> >> that is that per what little data I have, the average TCP transfer is on
> >> the order of 15K bytes, which is about ten 1460 byte segments.
> >
> > It only "disables" it if there was no congestion to control in the first
> > place.
>
> How do you turn off something that's not on?
>
> I refer to this as in the average case turning off congestion control
> because the transmission requires ten data packets and they all get sent in
> a single burst. There is no congestion control, with IW=10, in the case of
> the average-sized (which is actually gar above the median-sized) file
> transfer.
>
There surely is CC involved even if app only sends < 10 packets and some
packets got dropped.



>  > Could you on your behalf answer how does IW=3 affect parallel sessions
> on
> > the same kind of environment? ...I've done research on this (and Jerry
> has
> > too) and I know that the answer is not an intuitive one. Then we changed
> > to IW10 in the same environment and observe no (consistent) change. The
> > results are driven by problems already with IW3 so IW10 won't make it any
> > worse or the effect is just too small to be measured among the other
> > troubles that happen.
>
> That may be true. I have asked to see data describing the impact. I haven't
> seen the data. Maybe I missed something?
>
The NCSU lab has released the raw test data (result presented in IETF).
http://research.csc.ncsu.edu/netsrv/?q=content/iw10#data


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