Is this throttling? Torrent spikes at start, then drops to 1 MB/s

[creedo]

I know this is a common question and I've done some searching,

and played with all the appropriate settings. I read http://forum.utorrent.com/viewtopic.php?id=15992

and played with stuff like tcp ratecontrol, lazyfield, half open connections, etc etc.

Every time I start a torrent, I spike to 2.2ish megabytes (2,200 KB/s) within seconds.

I only can keep that speed for a few seconds then it drops to almost EXACTLY 1 megabyte (1000 KB/s)

and stays there. At any time I can stop, restart, and it will do the exact same process.

Speedtest.net using the nearest server reports my connection as 20 megabit down/3 megabit up.

I can see my ISP (Comcast) throttles but I'm curious if 1 MB is a comcast speed cap or something else.

Any other comcast people see exactly 1,000 KB/s? Glasnost reports no download throttling but

I understand the test isn't perfect. Also if I DL a large test file (not torrent just http),

I never see more than 1100 KB/s.

1000 KB/s is pretty fast so I'm not unhappy really, just curious what's happening.

I also want to know if there's a workaround, enabling encryption is not working.

Other info:

I'm using utorrent recommended settings, except for the recommended changes in the link above.

Using a surfboard cable modem, no router. Decently fast Windows 7 machine with nothing else running,

no firewall etc. Could the 2.2 megabyte number I see briefly just be wrong, or something the NIC can't handle?

[Switeck]

What you're seeing is ComCast's SpeedBoost in action.

Here it is on the upload side for me:

http://img821.imageshack.us/img821/4795/comcastspeedboost201008.png

The problem is...your sustainable upload is probably much like mine. It may spike to 2.5-3 mbit/sec but it won't sustain nearly that high! Which means uTorrent's settings *NEED* to be set based on having a 1-2 mbit/sec upload speed max rather than that short burst speed max.

[creedo]

Hi again - thanks for the heads up.

So just so I'm clear, either comcast is temporarily allowing more upload than I've really got...

therefore my unused download bandwidth gets used for a few seconds...

or my download gets temporarily boosted, and it's really capped at around around 10 megabits even though

speed tests show twenty.

I tried playing with different upload settings but whether I was uploading with lots of slots and 250 kb/s or

just a few slots and 30 kb/s, the download never improves over 1 MB/s. Even with several well-seeded torrents.

Eventually limiting the upload would result in less than 1,000 kb/s download.

I guess if I understand this right, it never will improve, except for when the torrent first starts.

So my next question is... is there some trick to getting utorrent to stop and start every few seconds,

to take advantage of comcast speed boost?

[Switeck]

Burst speeds do not work very well with uTorrent's assumed-fixed max speed limits.

You have to basically treat them as not existing.

The "extra" speed you get from burst is often only the amount you COULD have used had you been very near max regular speed all the time. It is not extra beyond that amount.

So your max upload stabilizes at 250 KiloBYTES/second in uTorrent even over 10 minutes time?

I'm not sure which ComCast speed plan you have. Can you check that via looking at your last bill?

I have the 6 mbit/sec down and 1 mbit/sec up plan...although they can burst to about double that amount.