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> HOW TO: Improve your UPLOAD Speeds, By increasing DefaultSendWindow
Eric Martello
  Posted: Aug 20 2009, 09:47 AM
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I used to have Comcast Internet with like 8 Mbps down and 1.5 Mbps up or whatever it was, but now I have FiOS 20 Mbps up and down. The problem was that I could download fine but my upload maxed out around 2 Mbps! WTF!? It was 10x slower than it should have been.

Then I learned about DefaultSendWindow and the fact that it isn't properly set on Vista machines but it is set in Windows XP, believe it or not. For a while I was wondering why my Windows XP laptop could do 10 Mbps up over WiFi while my wired desktop could only do 2 Mbps.

In both cases, the DefaultSendWindow needed to be changed, here's how:

1) Regedit:

HKLM\System\CurrentControlSet\Services\AFD\Parameters

2) If the DefaultSendWindow value is not in there, you will need to add it. Right-click on the right column and choose "New > DWORD Value (32-bit)" and name it DefaultSendWindow. Make sure that you enter it exactly like that, with the first letter of each word capitalized.

3) Calculate your ideal DefaultSendWindow value by using this easy formula:

(Upload Speed Kbps / 8 ) * 1024 = DefaultSendWindow

Example:

Advertised Upload: 15 Mbps = 15,000 Kbps

(15000 / 8 ) * 1024 = 1920000

- For those of you who don't know, the asterisk in the formula above means MULTIPLY.

4) Once you have the value, double-click the DefaultSendWindow value and make sure the "Base" part is on Decimal. Enter the number you got from the formula above into the value field, then put the radio button on "Hexadecimal" and click OK. The value needs to be in hexadecimal format for it to work right, but it is easier to calculate the optimal value in decimal format so that is why I said to enter it in decimal then change it to hex before saving.

4) Restart your system and then go try out a speed test from the links below and see how your upload speed is. Choose the server closest to you to get the best result:

Recommended Speed Test Sites

http://myspeed.visualware.com
http://speakeasy.net/speedtest

Eric's Notes

Note 1:
If some idiot tells you that changing the DefaultSendWindow doesn't make a difference in Windows XP or better because it "automatically adjusts" then tell him to go suck a cock. Setting the value WILL improve upload speeds because the default settings on XP and up WERE NOT designed with high speed TCP/IP uploads in mind. High speed being over 5 Mbps in most cases.

Note 2:
Yes, there is such thing as DefaultReceiveWindow but this value is commonly tweaked by most TCP Optimizers while the send window is left untouched.


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Eric Martello
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