BitTorrent is a peer-to-peer protocol designed to transfer files. Users connect directly to send and receive portions of a file, while a central tracker coordinates the action of all peers and manages connections without knowledge of the contents of the files being distributed. With BitTorrent, users upload at the same time they download, so network bandwidth is managed as efficiently as possible. BitTorrent is designed to work better than other file-transfer protocols as the number of people interested in a certain file increases.
How Does BitTorrent Work?
Fig. 1. A peer connects to the .torrent server to get the .torrent file (green line). The peer then connects to other peers within the network to simultaneously download multiples parts of the same file.
The BitTorrent protocol works by breaking up a file (an MP3, for example) into much smaller pieces, typically on the order of 1000 pieces per file. A .torrent file (henceforth “torrent”) is created containing information about how the file is broken up. This torrent is a “pointer” file—that is, it contains meta information about the file’s size and filename, but does not contain any of the file itself.
Peers (those hooked into the file sharing network) are then able to download or upload a torrent to a tracker, which is a piece of software on a web server the does nothing more than store and distribute torrents (the tracker does not house the actual files themselves). When a peer downloads a torrent from the tracker, the peer’s BitTorrent client uses this file in combination with the tracker to download many pieces of the file simultaneously from peers all over the world, and reassemble the file on the peer’s computer (Pouwelse, 2004).
The use of the BitTorrent protocol on the web creates a M:N network. A peer can connect to n other peers, creating, in effect an ad hoc distributed file sharing network (called a “swarm”) based on a particular file (Fig. 1). This is in contrast to traditional file sharing networks, such as Napster or Gnotella, which connect peers in a 1:1 model only.
The BitTorrent Controversy
BitTorrent has been the source of much controversy since its invention. As it is used by a large number of illegal file-sharing websites, these websites have become targets of the Recording Industry Association of American (RIAA) and the Motion Picture Association of America (MPAA) —the music industry and movie industry watchdog groups—and the technology has become synonymous with illegal file-sharing.
In 2004 civil lawsuits from the MPAA resulted in the shutdown of SuprNova.org, a popular BitTorrent site (Cullen, 2004). In May of 2005, FBI and Customs Enforcement agents executed 10 search warrants in nine U.S states in a strike against a torrent forum accused of providing links to copyrighted movies. This action is believed to be first criminal law enforcement action against BitTorrent users (Poulsen, 2005).
Despite these lawsuits, the MPAA has been quoted as saying it does not believe the BitTorrent protocol to be illegal. It has no plans to target BitTorrent technology—only those using it for illegal purpose (Poulsen, 2005). And also despite these lawsuits, many torrent sites that point to copyrighted materials continue to stay open and operate under the noses of the MPAA, the RIAA, and the federal government. One of the most prolific and seemingly immune is the Pirate Bay, a file trading site run out of Sweden. Despite its high profile and the many threats against it, it remains in operation. Undoubtedly, this is in part due to the fact it is run overseas, outside the reach of the U.S. legal system. Although trading copyrighted material is illegal in Sweden, the anti-piracy groups in that country have yet to bring the site down (Harrison, 2006).
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