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

[Jerry Chu <[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.
>
> > 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?


Have you chosen not to see the data, or you've simply forgot we've done some
testbed
study with results presented at TCPM (which you missed due to prior
engagement)?

One of the purposes for this round of our testbed study was to investigate
the questions
you've raised. If you have still issues with the result, e.g., you have a
different set of
parameters in mind than what were used by our tests, please spell them out
and we
can hopefully get the results for you quickly (well I'm still in travel so
it may take a
couple of weeks).

Jerry