So, it seems that you can not enforce TcpWindowSize anymore. It will default to 64KB for > 100mpbs and will change beyond 64K only if the other side also supports RFC 1323. The latter doesn't seem to work because on colinux windows scaling is enabled and iperf is asking for a window size of 640k. It could be a bug with their recent changes in XP SP2.

what a shame that the loopback which reaches upto 350Mbps in iperf tests with custom window size from colinux->windows can't do more than 32mpbs with windows defaults.

its freaking order of magnitude difference and its not colinux's fault. something else is at play here....

Thanks,
-Sunil
PS: the information about tcpwindowsize was based on:
http://technet2.microsoft.com/WindowsServer/en/Library/db56b4d4-a351-40d5-b6b1-998e9f6f41c91033.mspx

and I am assuming that most of the changes are part of XP SP2.

Sunil <funtoos@yahoo.com> wrote:
>> You have also to check/set GlobalMaxTcpWindowSize and
>> change Tcp1323Opts to 3.
 
Both these parameters are set as well.
 
GlobalMaxTcpWindowSize is same as TcpWindowSize. Tcp1323Opts is 3.
 
any more ideas please?
 
Thanks,
Sunil


Ren� Berber <r.berber@computer.org> wrote:
Sunil wrote:

> I tried to set TcpWindowsSize in windows by changing the registry but
> the value used is still 64 kbytes. Anyone know if windows xp sp2
> discards the value in
> HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters,*TcpWindowSize*
> **
>
> I have it set to 255500 but iperf still shows 64kb as default. Online
> tests confirm this value of rwin.
>
> I don't know why it doesn't use the value. I will appreciate some help.

You have also to check/set GlobalMaxTcpWindowSize and change Tcp1323Opts to 3.

Ref: http://rdweb.cns.vt.edu/public/notes/win2k-tcpip.htm
http://www.psc.edu/networking/projects/tcptune/#Win2k
--
Ren� Berber



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