Single torrent fast, multiple download slow.

[qwertykeyboard]

Recently I've been experiencing some seemingly random issues with download speeds and internet connections when dealing with torrents. Before someone automatically posts links to the standard guides, I'd like to point out that I've already read through all of them and tested god knows how many combinations of settings to adjust the performance.

The main issue that I've been experiencing relates to having multiple torrents running simultaneously. The latest test was with a pair of torrents that individually have great speeds. We're talking about 400-600 kB/s (that's kilo-bytes) sustained. However, when I try to run both simultaneously, their speeds drop to ~20-30 kB/s. Mind you, this isn't with all torrents and it doesn't seem to be limited to particular trackers either. Any ideas what could cause this?

The other issue that sometimes shows up is the nuking of the internet connection when running these downloads. With some torrents, it becomes nearly impossible to access the internet via another application. This obviously isn't a problem right now, but when it happens, the only fix is to shut down uTorrent and reboot the modem. It seems to happen more often with one particular tracker that's given other problems anyways. This leads me to suspect that a number of my issues are actually tracker related rather than ISP or application settings.

For those interested, my settings, etc:

=============================

ISP: Cox

DL/UL: 6.5 mbps/ 1.5-3.5 mbps (depends on test site)

uTorrent:

BitTorrent:

Max UL: 186 kBps

Max Global: 250

Max #/Peer: 80

# UL Slots/torrent: 7

Protocol Encryption: Enabled/Allow Incoming Legacy

DHT is enabled.

Queueing:

Max # Active total: 8

Max # Active DL: 6

I don't have NAT issues, and usually have a great connection. I'm just trying to figure out what could cause these problems.

[Switeck]

With 1 torrent, your upload speed is split 7 ways...but still probably greater per peer you're uploading to than most others. So almost every peer you upload to uploads back to you.

You start 2 torrents, now your upload is split probably 14 ways...and numerous other peers can and are uploading significantly faster than you. End result, they get the lion's share of other peer's upload speed.

[qwertykeyboard]

Ah, that makes sense. So, would reducing the UL/torrent number help for multiple downloads, or is that just a bad idea?

[Switeck]

Ok, so you currently have 2 torrents started with 7 upload slots each (14 upload slots total) and max upload speed of 186 KiloBYTES/second. Assuming you're always getting full upload speed (which you probably aren't!), that is an average of 13.2 KiloBYTES/second per upload slot (per person) that you are uploading to at any given moment.

With only 1 torrent going, that is an average of 26.5 KiloBYTES/second per upload slot (per person) -- faster than some peoples' total usable upload speed! You must have a large list of peers to pick from on whatever torrents you're downloading, because usually for me I seldom see individual peers uploading to me much faster than 10 KiloBYTES/second.

Were you to lower upload speed, other peers would be less willing to give you as much of their upload speed IF there were any other peers uploading to them as fast or faster than you.

Is uTorrent really sustaining the 186 KiloBYTES/second upload speed on its speed graph?

[qwertykeyboard]

Yes, it does sustain that speed. These problems aren't with all downloads though. A couple of trackers I regularly use let me easily pull 3+ downloads simultaneously for ~600-700 kB/s.