Gathan Beaga

ask alan: bittorrent

I’m not sure exactly why Mr Reasonable thought I could give advice on this… but I’ll try. Especially as there’s some free caffeine involved.

Bittorrent is a way to efficiently distribute large files in a way that lessens the chance of choking the bandwidth on the file’s host. It does this by chunking the file up, and allowing people to download the chunks from each other. So if Martha and I are both trying to get hold of the latest out of copyright Kiddie Records file and I already have chunk 5 downloaded, and Martha needs it, then she downloads it off me rather than looking in a possibly overloaded central place for it. In this way, you end up with a “swarm” of downloaders all obtaining chunks of the file off each other at quite high speed.

As I understand it, this is very efficient, and also takes advantage of the fact that most people never use their 128kbps upload capability with their broadband connections. In most cases users should end up uploading to others almost as fast as they are downloading.

This is all much better explained here and more technically here.

Anyway, Mr Reasonable’s problem does sound like a firewall problem. He’ll need to dig around in his PC’s firewall and open ports 6881 through 6889 to incoming connections so that people on the network can request stuff back off him.

Also, I would recommend him trying Azureus instead, a Java based client that has quite a nice wizard-based setup that is aimed at beginners and experts. Works good for me.

So Mr Reasonable: see how you go with that. If it’s still not working right then you may have to do some configuration of your ADSL router. Hopefully not though: Azureus supports a protocol called UPnP which talks nicely to many newer ADSL routers. (I ended up having to upgrade the firmware of the router – not for the fainthearted – to get UPnP to work seamlessly. I’m sure there was an easier way, but I’m not savvy enough to know.)

All good fun though. Now, is this sufficient for coffee?

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