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

[Fred Baker <[e-mail]>]

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?