February 1st, 2009
P2P file sharing traffic can constitute up to 75% of all the broadband bandwidth depending on the country. This of course increases the cost of operation for the ISPs, since it means traffic congestion and slow internet for them which leads to unsatisfied customers.
To solve this problem they either buy more traffic, or they limit the p2p traffic. Businesses being businesses - maximize profit, minimize cost - some of them go for the second option, that is to limit the torrent traffic of their customers.
How to check if your ISP limits your torrent traffic?
This tool called Glasnost can check if your ISP is manipulating your torrent traffic. It takes 7 minutes to make a full analysis of your ISP.
Test on my ISP (Streamyx) returned a negative result for the main port 6885, even though Streamyx is in the Bad ISPs list that are known to throttle the torrent traffic.

Maybe I have not reached the limit yet? Glastnost’s note could be the explanation:
Note: that some ISPs do not throttle all BitTorrent traffic but only if this traffic exceeds a certain threshold. Thus, passing our tests does not necessary mean that there is no throttling occurring on your link.
That’s probably correct since I am not a heavy p2p user.
Website: broadband.mpi-sws.org/transparency/bttest-mlab.php