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Whole internet slowdown whne µTorrent downloads


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I just changed from Azureus to µTorrent and I noticed a BIG slow down on my internet connection... I've read a couple of posts about this problem and I don't believe this is an isolated Issue.

Alright, here's my setup :

10mb/1mbit cable

(~1200k/sec download with 120k/sec upload)


-> Running WIndows XP SP2 with patched tcpip.sys to allow 500 connexions..

-> Running µTorrent with the followings settings : max connection globally : 400, max connection/torrent : 125, max half-open connections : 10


-> Running WIndows XP SP2 with patched tcpip.sys to allow 500 connexions..

-> Running IE6 / Firefox...

Both connecter on a Linksys WRT54G V2 with linksys firmware on a Scientifix Atlanta Webstar cable modem

Using azureus, everything is fine (same max connections/max connection per torrent setting, same port, same torrent, same max upload, same max download) but when using µTorrent everything is REALLY slow.. I can't play any online games (getting + 2000ms latency) and browsing the web is a pain.

I believe this is due to HOW µTorrent handles the max download/upload... but since it's not Open Source.. I can't check the code myselft...

I set µTorrent to max 80kb U/L and DU Meter reports 100-105kb/sec all the time. When setting 80kb U/L on Azureus, I get 78-80 on DU meter. I think that Azureus calculate the overhead of the bit torrent protocol BEFORE it limits the banwidth... and µTorrent simply calculate how muich of the data itsleft is transfered... limit that then encode the packets and send them.

Setting Azureus to 105k/sec U/L gives the SAME results as µTorrent at 80kb/sec

See for yourself :



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You're not using your connection for any other reason besides testing, while you're testing, right? Including all other comptuers that might be on your network?

Anyway, you should test several times. Select the average upload speed from the Speed Guide. If it doesn't match nicely (off by more than 10% or so from the upper one), pick the lower one.

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ok, just tested a few times, from different servers, and I get about 840-860 kbps upload...

Speed guide recommends : 72kb/sec upload, 450 max connections, 100 max/torrents

I agree that overhead is probably taken into account... but there is something wrong with the speed limiting.. the speed is not as stable as with azureus.. it goes over and under the limit all the time.

While I agree that 80k/sec was a bit high for my upload speed... it was working fine on azureus because it was never actually going over 80. With µTorrent, it probably averages 80k/sec but it goes higer than that... see my screenshots...

I'll test with a lower max upload and gives you feedback

Thx for your quick answers ;)

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If your line is capable of the speed, µTorrent will hold the upload speed within 3 KB/sec of what you set it to.

Azureus is probably only showing you an average speed and may fluctuate just as much as µTorrent. It seems very odd that in the Azureus screenshot DU Meter is showing LESS upload bandwidth being used than Azureus claims to be uploading. ONE of them is misreporting, and probably by >15%.

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