Strange effect

[spyder]

Hi.

I have observed a strange effect: I can have a torrent coming in at some puddling low speed; maybe there are few active seeds or peers...

I start a second torrent downloading and immediately the first one comes to life and the download speed increases dramatically.

Is this a normal thing? If so, what is the reason?

Regards

[Ultima]

Coincidence?

[Switeck]

It may occur if you have very strange settings, especially advanced settings!

Can you list all the settings shown in Speed Guide (CTRL+G) as well as any non-default advanced setting?

[spyder]

Hi.

It's not a coincidence, I've observed this on a number of occasions.

The Speed Guide settings are "default" – ie, based on the up and down speedsindicated by the speed test sites, and are as follows:

Up Limit – 7kB/s,

Up Slots – 1,

Connections – 50,

Connections (Global) – 75,

Max active up – 1, Down – 1.

I've changed nothing under "Advanced".

[Switeck]

Ah, with only 1 upload slot...it acts like the optimistic unchoke slot alot.

But how could starting another torrent work? You've limited total active torrents to 1.

...unless you have the slow torrents don't count towards the limit feature enabled.

If you're only running 1 torrent at a time, set your upload slots to 2.

[spyder]

Now that was interesting. I changed the upload slots to 2, and the download speed of the one torrent being downloaded doubled!

So... Does that mean that it wasn't the Forced starting of a second download that affected the speed, but the associated uploading of that second torrent?

Whatever - thank you.

[Switeck]

I don't know how µTorrent handles optimistic upload slots across multiple torrents at once, but that'd be my guess.

Problem with optimisitic upload is it's randomly choosing people to upload to, NOT choosing the person who gives you the most back in return. Because of this, you get random download speeds in return...usually poor results, such as 3 KB/sec at most from people -- even seeds.

[spyder]

Ah. I see. (I think...)

So, what if I make it 3 slots?

Or increase the Global maximum Upload rate?

[Switeck]

If you can, do both -- but remember to keep TOTAL upload slots (upload slots times number of active torrents) below the upload speed's KB/sec...preferably only 1/3 as much.

So if you had upload speed set to 9 KB/sec, that'd mean 3 upload slots but only 1 torrent at once.

Reason for this is...if each upload slot of yours is less than 3 KB/sec, you are far less likely to get much of anything back from anyone you're uploading to...as many others are no doubt uploading to them faster than you.

[spyder]

Thanks for the advice and help - I think I'm beginning to understand this torrent business... I think...

Now - I have one torrent downloading, and another one seeding. How does one affect the other?

(If the questions are becoming stupid and/or tiresome, please say so.)

[Switeck]

Still, like you say, with 2 torrents going at once I don't really know/understand why 1 would affect another except to slow it down -- since they're both fighting over limited bandwidth!

[spyder]

OK, thanks. I sort of thought that theupload and download bandwidths were somehow distinct and separated.

Anyway - my initial query has been more than satisfactorily answered. Once again, thank you for your interest and patience.

[Switeck]

BitTorrent file traffic goes over TCP IP. That means each packet that is received/downloaded on your end has a smaller upload/outgoing SYN ACK reply. And each packet you upload should get a SYN ACK reply on your download. But if your upload is so overloaded that random packets are lost, SYN ACK replies gets lost often too and your download slows also. The same is true for download being maxed out, though that condition is alot rarer due to most people having max download speeds 10-20x their max upload speeds.

In English, you're not working in a vacuum. The speeds you're getting is negotiated on-the-fly with the others on the torrent. If your connection fails to send the "send more!" (SYN ACK) packet quick enough, the other end quits sending as fast.

Lots of people don't know how to unfirewall their connection for BitTorrent. Probably nearly as many just use whatever default settings their BitTorrent client uses...which means either very low upload speed limits or NO upload speed limits, which is even worse. With no upload limits, they're usually slamming hard against their ISP's upload limits and their ISP randomly destroys their uploaded packets to get them back under max speed. End result, they may only be averaging about 50% of their real max upload speed.