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I am downloading the new Ubuntu release, and the speed fluctuates a lot. By a lot, I mean it is 500 kB/s one minute, and 1 kB/s the other (not exaggerating). It seems to have slow and fast "periods".

I am using the latest uTorrent on Windows XP, currently there are 41 seed connections and 9 peer connections.

Any idea what might be causing this?

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could be a few things... best guess is attempted throttling by ISP but then you'd see it on all torrents. Maybe you need to forward/open the ports bittorrent is using? utorrent would show the yellow warning icon at the bottom right if it's that. Polluted torrent with lots of fake pieces? Unlikely for an official ubuntu torrent from the site. Usually when I experience that it's when there's a lot more peers than seeders... the seeders get a few pieces out, they spread, then people are stuck waiting for the next batch of pieces (the 1kbps is just overhead and is actually 0). – CreeDorofl May 1 '11 at 1:27
@CreeDorofl: I don't use it that much, but it happens with pretty much everything that I try to download. I guess it could be the ISP then? The icon is the green checkmark so everything should be ok. – houbysoft May 1 '11 at 2:21
ever manually tweak the utorrent settings? It's got some weird advanced settings that might cause that, but most people leave them alone. You might reinstall and then run the speed guide (ctrl+G) to get ideal settings. Then you could try forcing protocol encryption, might fool the ISP into not throttling the bandwidth. Ctrl+P for preferences, then bittorrent on the left. – CreeDorofl May 2 '11 at 2:04
If your upload speed setting is using all your up bandwidth, then there is not room for other important packets to be sent to other seeds and peers, you need to throttle your upload bandwidth to 80% or less of your available up bandwidth from your ISP. Check your settings. – Moab Jun 17 '11 at 14:11

Since you are using XP, have a look at your System Event Log for Event ID 4226 "TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts". Microsoft introduced a limit on the number of concurrent half-open TCP connections in SP2 of XP and this can often be hit with torrents.

For more information see How to adjust your Windows XP TCP Connection to boost your BT download speed? which includes a link for adjusting the number of TCP connections.

It would also be worth looking at some of the TCP Tuning tools, such as SpeedGuide TCP Optimizer as XP doesn't have a well tuned TCP/IP stack as the ones in Vista or Windows 7.

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Perfect, it also worked on Windows 7. Two years after, your answer is still pertinent! – gaborous Oct 19 '13 at 22:22

Do not tweak your uTorrent or any other torrent client's settings. Just keep it with its default settings! Update your uTorrent and you are good to go.

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