A BitTorrent user who has downloaded a file may use it immediately or share it with other users through a BitTorrent tracker. In either case, if the user has more of the data in a torrent, or for that matter, the entire torrent, he or she will be able to download it more quickly.
The BitTorrent protocol has been adopted by a number of Internet service providers. After a torrent is created and a data center is set up, the content on the site is moved to the BitTorrent network. Users requesting the content are connected to the site using the BitTorrent protocol. This has the advantage of being more cost-effective than a traditional distributed system, since the content is no longer stored in a single location and sites no longer need to pay for bandwidth in large quantities. A disadvantage is that bandwidth is shared among users of the site, lowering the available bandwidth and resulting in slower download speeds. To combat this, hosting providers provide users with a higher bandwidth package (often, they are charged only for the difference between their desired bandwidth and the available bandwidth).
What remains to be seen are the legal implications of BitTorrent and peer-to-peer networks. Although the BitTorrent protocol itself is not covered by copyright law, the distribution of copyright infringing material through BitTorrent may be illegal. This problem is compounded by the fact that the BitTorrent protocol does not enforce copyright licenses - if a file is not covered by a license, peers may download it as they see fit and share it with other peers.
BitTorrent is used to share a variety of types of files, ranging from software, movies and music to games and pirated content. It is possible to use the BitTorrent protocol to share various types of files, as illustrated in Figure 1.
Figure 1: Distribution and sharing of a file with a single torrent. The content is available at the web site.
A central concept of file-sharing networks is that the peers in a network share content. The torrents and trackers of BitTorrent and other file-sharing protocols are centrally coordinated infrastructures, since files are distributed by the peers and the peers cannot do anything else. This is in contrast to other file-sharing systems where peers merely upload and download files. The centralization of the peers is of course also a problem from the security point of view. This section describes some public distribution systems that try to address this problem. 827ec27edc