Again and again the problem arises that with BitTorrent downloads Traffic Shaping does not function well. We checked the problem and found out here through tests, that the RX-rate drops, if you download with too many connections simultaneously.
The result of our tests is: Downloads are substantially faster and Ping-times better if one limits the amount of the connections to for example 50 in the BT-client.
Below follows documention regarding the issue. Unfortunately so far we haven't found the exact reason for this problem.
Tests were run on a DSL-16000/1000 connection provided by Deutsche Telekom with a 1950kb/128kb flow-rate. Testing occured via constantly reloading Debian CD-Images with uTorrent 1.6.1 every 30 minutes.
This is what the transfer looks like with the limitation of 50 connections maximum:
The mean DL-rate scored at 1613 kb/sc, the mean ping at 63 msec.
And with 850 connections:
The mean DL-rate scored at 1009 kb/sec, the mean ping at 97 msec.
Meaning: It is neither advisable for appropriate ping times nor for fast downlaods. On top of this the many connections also play out on CPU load (with about 50% used rather than about 25%).
This effect has emerged earlier when dealing with a DSL-2000 connection and azureus. This does not seem to be the cause here, though. Furthermore it does not make any difference whether RX-Shaping is switched off or on.
We are continually working on an explanation as well as a solution for this problem. Until then we can offer only one measure, that is, however, very simple: Limit the amount of connections. We recommend a value of 50. Torrent clients will only decrease the amount of connections when a download is completed or if you restart.
cFos and cFosSpeed generate a Windows - Balloontip, once so many connections transfer data that RX-shaping can hardly stop them anymore. This is the case at 30 or more connections.
cFos and cFosSpeed always generate these baloon tips if rx-shaping has reduced connections to a maximum for 10 seconds at a time. If other connections are added at this point cfos and cfosspeed respectively is no longer able to keep the port regarding rx from being congested and ping rates increase.
If this balloon is, however, undesired and the user is not able or does not want to reduce the amount of used connections he or she can switch off the ballon with the command spd gset balloon_many_cons 0 -save.
Any comments pertaining to this topic should be posted here: cFos Forum