In our friend’s case, he was using a BitTorrent client called Azureus. The standard BitTorrent client is written in the highly flexible Pyton language. Azureus is written in Java, which can be slower than Python, but Azureus works on both Windows and Mac OS X, and it’s much better looking, more configurable and provides a lot more information and potential for tweaking than most of its competitors.

Bleeding Edge, however, prefers to use the Windows client called simply BitTorrent, which is now at version 4.01. It’s fast and very simple to set up, and we particularly like the slider feature that allows you quickly to change the amount of bandwidth you devote to uploading, while downloading a file.

That’s the first thing the BitTorrent user has to come to terms with. Unlike other peer-to-peer programs, BitTorrent works on the principle of sharing. You have to devote some of your upload capacity to give the file to others while you’re downloading it. In order to get the best out of these “swarming downloads”, you have to finely balance your uploads to maximise the speed at which you get the file. We generally set it at between 7 and 8k.

The other thing is that BitTorrent isn’t as nicely “wrapped” as other peer-to-peer programs, so it’s not easy to use, or to find files. Simply identifying a reliable source of torrents can be difficult. You may have to trawl though on-line forums or watch IRC channels just to find the torrent you’re looking for. The ones you come up with could be dead, or painfully slow.

If you’ve got a firewall – and we sincerely hope you do – you’ve also got to set it up to allow BitTorrent to accept incoming connections from the Internet. If you have a router, you have to set up port forwarding. If you run a software firewall like Zone Alarms or Sygate, you will have to open the ports used by BitTorrent.
In the case of Azureus, the default is 6881. BitTorrent seems to require 6881 – 6889. In practice, however, some ISPs throttle back those ports, so it might be wiser to set it to something like 4881 etc.

Most BitTorrent clients seem to allow you to set the exact IP address you’re using. If you don’t have a static connection, you can find out what that address is here.

Most peer-to-peer programs centre around a search program that helps you find what you are looking for. Then you tend to download off a small group of clients. BitTorrent has no built in search engine - it simply deals with the mechanics of downloading. Before you can even start, you need to find a .torrent file. They’re very small, and they contain information about the file you want to download and the location of a “tracker” that is looking after the torrent.

A couple of good sources are here and http://www.btefnet.net.

The tracker is the only centralised part of BitTorrent. It doesn’t hold any files. It merely tracks who is interested in them, and sends Bit Torrent a random list of peers that are also downloading the same file. BitTorrent then negotiates with the peers what to download.

Centralised downloading systems tend to fall over as the load increases. The genius of the BitTorrent architecture is that the more popular a file is, the faster everything goes, because there are more peers to share the load.

Bittorrent works by slicing the file up in to little pieces so a 300
MB AVI file may get dived into 600 512Kb pieces.

BitTorrent will try to download a piece at a time from as many peers at it can. By default, it goes for the rarest piece first, making it more likely you’ll get the entire file in the shortest possible time. The client may show a linear progress bar, but in reality you download the files in almost random fragments.

BitTorrent is used to download many things that don’t breach copyright. Many Linux distributions are available as torrents and there are sites like filerush.com that use BitTorrent to distribute game demos and trailer videos. We’re almost sure that’s what our friend was doing.