Bittorrent FAQ
Traditionally, files are downloaded from the Internet by accessing the file from a single server. The file is downloaded in sequential order. You can download the file only if there are enough resources on the server to handle the connection and if the file remains available. The BitTorrent protocol was created by Brian Cohen in 2002 to offer an alternative to the single-server, sequential download method.
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The Basics
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BitTorrent is an Internet protocol that allows users to download files quickly by allowing the people who are downloading the file to distribute parts of the file as they are downloading. It is used to distribute large or very popular freely available files. The BitTorrent protocol rewards users who provide the most upload capacity by providing them with a faster download. However, users with limited bandwidth can participate in the file transfer.
How It Works
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The first user creates a torrent file that contains the meta data about the file and information about the computer that will coordinate the file distribution. This coordinator is called the tracker. The file is then provided to other users to download.
Other users (peers) obtain the torrent file and connect to the specified tracker and the original user to begin downloading the file. Each peer that connects to the file is provided with a different portion of the file. When multiple peers have multiple portions of the file, the peers begin to distribute their portion of the file. When a peer finishes the download of the complete file, the peer becomes a seeder for that particular file, further reducing the resource load for the original file distributor. The seeders and peers together are called a swarm.
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Advantages
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The BitTorrent protocol reduces the strain on the original distributor's hardware and bandwidth resources. Instead of making a large data request over a single TCP connection, BitTorrent makes many small data requests over multiple TCP connections to different computers.
It also provides redundancy against system problems and the dependency on the original distributor. If there are multiple seeders and peers for a particular file, the download can continue even if the original distributor removes the file.
Files are downloaded in either a random method or a "rarest first" method, instead of the traditional sequential method. This ensures the high availability of the file.
Disadvantages
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Unlike traditional downloads, where the download speed reaches a certain level and then remains at that speed until the download is finished, BitTorrent downloads take time to reach full speed. This is due to the time it takes to connect to peers and the time it takes a peer to receive enough data to become an uploader. BitTorrent downloads slowly gain in speed, then slow down as the download finishes.
There is also no way to index torrent files. Because of this, the material that is available from a few websites may be copyrighted, and there may be legal implications for downloading the files.
There is security risk in using BitTorrent rather than traditional methods. It is possible to obtain the IP addresses of all the participants in the swarm from the tracker. Users with insecure systems can become vulnerable to a malicious attack.
Client Software
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To download files through BitTorrent, you must have a BitTorrent client. There are several clients available, including the original BitTorrent client, uTorrent and Vuze. BitTorrent and Vuze are available for Windows, Mac OS X and Linux. Utorrent is available for Windows and Mac OS X.
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