Need bigger TCP receive window on VISTA PC
Dear Vista experts,I connect to internet using my wireless modem which can be best described as high BW and high latency connection. At best it should provide a BW of about 7Mbps and has a rather large RTT. Under this conditions I have to set a large TCP window size to achieve the maximum throughput. Windows 2000 and XP allowed me to alter this parameter in the registry. However in Windows Vista it seems as though this control is not available anymore.I am aware of the feature in VISTA to auto tune the RWIN and window scaling. But no matter what options I use in 'netsh' I get only about 1.7Mbps. Where as in windows 2000 and XP I can get 6Mbps and more because I am able to set the parameters in the registry. I see that Vista PC is always keeping the window size to 64K (and with scaling it is 8K x 8). How can this behavior be changed. I need to have larger window size for my setup.Kindly suggest a solution.Regards,Vijay
October 24th, 2008 4:32pm

Hi, The option to set the Window Size is not available in Windows Vista. Windows Vista uses the Next Generation TCP Stack which: - Does not have the option to manually set the Window Size. - Has the Auto-tuning Feature which has Receive Window Auto-Tuning enabled (default) The next generation TCP Stack no longer uses the TCPWindowSize Registry Values. For more information, you can refer to the following link: http://www.microsoft.com/technet/community/columns/cableguy/cg1105.mspx Hope it helps.
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October 27th, 2008 12:19pm

Hi,Given below is a brief description of the observation made with the Autotuning and its effect on the TCP window size (in effect data rate):By default as you indicated the autotuning is set 'normal'. FTP data transfer was done with the ethereal tracing. From the ethereal traces I can see that during the FTP setup a window scaling of 8 (multiply by 256) is negotiated. However during FTP an effective window size of 16896 (66 * 256) is used.If the autotuning is set to 'restricted' then a window scaling of 4 (multiply by 16) is negotiated and during FTP an effective window size of 17040 (1065 * 16) is used.If the autotuning is set to 'highlyrestricted' then a window scaling of 2 (multiply by 4) is negotiated and during FTP an effective window size of 17040 (4260 * 4) is used.And if the autotuning is set to 'disabled' then a window scaling option is not used and during FTP an effective window size of 17040 is used.The different autotunning options only seem to change the scaling factor but the effective window size is more or less the same. In my environment I need to have a larger receive window size to get more data. What changes in the environment can help me in achieving a larger window size?Regards
October 27th, 2008 6:14pm

Hi, Based on my knowledge, we cannot change it. For more reference: http://support.microsoft.com/kb/951037 http://technet.microsoft.com/en-us/library/bb726965.aspx http://technet.microsoft.com/en-us/magazine/cc162519.aspx http://technet.microsoft.com/en-us/library/cc507851.aspx Thank you for your understanding.
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October 29th, 2008 11:04am

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