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Reducing upload speed raises download speed


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I have a 30Mbit full Duplex Line. I have tested this on many occasions and I can up- and download with 30Mbit simultaneously to FTP, Rapidshare, Speed Tests and so on.

But with utorrent there is this strange phenomena: when I reduce the upload limit to 10Mbit my download speed always enhances!

Windows 7 64 bit Enterprise

I have no router and no software firewall.

netmax halfopen is at 50 in utorrent.

I included a picture

It starts fast, when there are not as much downloads. Then it slows down. Then you see the download speed up again, thats when I reduced from 30Mbit to 10Mbit:


Have you any ideas? My speed is pretty good, I had utorrent downloads at 20 Mbits too, but i always goes faster when limiting the upload speed per torrent.

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I tried reducing it to 25 and 20, but ~10MBit it always gives me the best download.

At the moment I have a download with 850kb at 10MBit upload. I set it to 20;bit and dropped down to 650. Set it back, back at 850.

And why is an increased net.max_halfopen useless? There was this patch for Windows XP to allow more than 10 and it definitely boosted utorrent alot. But maybe this was coincidence?

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Thx alot for this information!


Upload speed always goes up to the maximum in a few seconds.


Full switched network to my house -> 100Mbit full duplex connection from the switch to the box in my apartment with glass fiber -> box limits it to 30MBit full duplex -> ethernet to gigabit card in PC, full duplex is on.

No modem, router, firewall (except from Windows 7).

I use PeerBlock when using utorrent.

My idea was that some seeder slow me down when upload is to high since some trackers want slower updates so the torrents stay online longer. I once was subscribed at one tracker that only allowed 500kb/sec maximum upload because of this reason.

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