BiTtorrent 101: The Complete Guide to Filesharing

The old school crew
Since the downfall of Napster in 2001, new networks sprung up to fill in the gaps, with FastTrack, Gnutella and eDonkey being the most popular. The FastTrack protocol lies beneath services like Kazaa, Grokster and iMesh, and relies on certain clients acting as supernodes to speed up file searching. Kazaa is the most recent to hit the headlines, after an Australian court found that the owners knowingly allowed its customers to trade copyright files. The upshot is that Australians can not officially download the client from the Kazaa website.

The eDonkey network uses dedicated servers to track and locate files, rather than relying on supernodes. eDonkey is a massively popular service, and according to research firm CacheLogic, is the most popular method for trading video files.

Gnutella takes a slightly different tack to eDonkey and FastTrack by delivering a pure, decentralised network. It was originally developed by Nullsoft developers, Justin Frankel and Tom Pepper of Winamp fame. While Nullsoft was working under AOL, the pair released Gnutella without AOL's knowledge. AOL subsequently canned the project, but the software (and source code) had already been downloaded in the thousands. Without a centralised server, the network can't be shut down -- once it's up, it's up.

Looking beyond the major players, there are many more networks lurking in the background. Some, like MP2P are exclusively used for music, and others will restrict clients from connecting unless they offer up a library of files to share. The net effect of the many networks, each with their strengths and weaknesses, provides a collective mesh of peers where you can find anything you want.

But is this just an industry built on copyright infringement? As a whole, few would argue that these networks didn't facilitate illicit filesharing. You could even take it a step further and suggest that these networks not only rely on it, but were created because of it -- something that the court house dramas over the past few years will attest. But if we look past the rampant piracy, there's a whole new world of legitimate P2P brewing out there.

It's raining bits
One of the most significant moments in Internet history is when lone programmer, Bram Cohen, unleashed BitTorrent in 2002. Prior to BitTorrent, if you wanted to distribute a large file you'd likely be charged through the nose in bandwidth, and the more popular the file, the more demanding the load on the server. Consequently, you either have an expensive server farm to keep up with demand, or your server would crawl to a stop as it tried to fulfill the many requests.

BitTorrent changes that by turning the process upside down. By using the bandwidth of each person who wants the file, rather than a series of one way client connections to a single server, popular files are distributed faster and cheaper. That a file could be better distributed with more people was an absurd notion five years ago, but for those that deal in large files, it's now an indispensable distribution method.

In order to start downloading with BitTorrent, you first download a very small file with a .torrent extension. The tiny files contain information about the original file, as well as the location of the tracking server. When the .torrent file is loaded into a BitTorrent client, the client contacts the tracker discover which peers have the data you need. Once you've started collecting data packets, the tracker will then let the other peers know, who'll then start asking you for data. The net result is that no matter how many users are after a file, there's little chance of a bottleneck forming -- and with more users, you'll often get a faster connection. Of course the reverse is also true, where an unpopular file will often be slower than a dedicated server, due to the lack of peers to download from.

Another distinction is its use of the web as a searching tool, where other P2P programs require direct searching of the shared files of other peers, or accessing a designated indexing server. Few search engines can compete with the speed of a Google search, and this a major strength of BitTorrent.

Given its advantage in distributing large files, the most common file types winging their way around BitTorrent networks are videos, games and software packages like Linux distributions. It also has a place in commercial online distribution services, with Cohen himself having been brought into Valve to work on its online distribution service, Steam.

Despite its uses in distributing copyright media, which constitutes the majority of BitTorrent downloads, its robust system makes it ideal -- and in some cases necessary -- for any type of large media. This alone helps BitTorrent attain an air of legitimacy, letting it stand apart from the pirate havens of classic P2P networks.