Bit Torrent:
Bit Torrent is a protocol for the practice of peer-to-peer file sharing that is used to distribute large amounts of data over the Internet. BitTorrent is one of the most common protocols for transferring large files, and peer-to-peer networks have been estimated to collectively account for approximately 43% to 70% of all Internet traffic (depending on geographical location) as of February 2009.In November 2004, BitTorrent was responsible for 35% of all Internet traffic. As of February 2013, Bit Torrent was responsible for 3.35% of all worldwide bandwidth, more than half of the 6% of total bandwidth dedicated to file sharing.
To send or receive files the user must have a BitTorrent client; a computer program that implements the BitTorrent protocol. Some popular BitTorrent clients include Xunlei, Transmission, μTorrent, MediaGet, Vuze and BitComet. BitTorrent trackers provide a list of files available for transfer, and assist in transferring and reconstructing the files. The most well-known BitTorrent tracker is The Pirate Bay.
Programmer Bram Cohen, a former University at Buffalo graduate student in Computer Science, designed the protocol in April 2001 and released the first available version on 2 July 2001, and the final version in 2008. BitTorrent clients are available for a variety of computing platforms and operating systems including an official client released by Bittorrent, Inc.
As of January 2012, BitTorrent is utilized by 150 million active users (according to BitTorrent, Inc.). Based on this figure, the total number of monthly BitTorrent users can be estimated at more than a quarter of a billion
Downloading torrents and sharing files
Users find a torrent of interest, by browsing the web or by other means, download it, and open it with a BitTorrent client. The client connects to the tracker(s) specified in the torrent file, from which it receives a list of peers currently transferring pieces of the file(s) specified in the torrent. The client connects to those peers to obtain the various pieces. If the swarm contains only the initial seeder, the client connects directly to it and begins to request pieces.
Clients incorporate mechanisms to optimize their download and upload rates; for example they download pieces in a random order to increase the opportunity to exchange data, which is only possible if two peers have different pieces of the file.
The effectiveness of this data exchange depends largely on the policies that clients use to determine to whom to send data. Clients may prefer to send data to peers that send data back to them (a tit for tat scheme), which encourages fair trading. But strict policies often result in suboptimal situations, such as when newly joined peers are unable to receive any data because they don't have any pieces yet to trade themselves or when two peers with a good connection between them do not exchange data simply because neither of them takes the initiative. To counter these effects, the official BitTorrent client program uses a mechanism called "optimistic unchoking", whereby the client reserves a portion of its available bandwidth for sending pieces to random peers (not necessarily known good partners, so called preferred peers) in hopes of discovering even better partners and to ensure that newcomers get a chance to join the swarm.
Although swarming scales well to tolerate flash crowds for popular content, it is less useful for unpopular content. Peers arriving after the initial rush might find the content unavailable and need to wait for the arrival of a seed in order to complete their downloads. The seed arrival, in turn, may take long to happen (this is termed the seeder promotion problem). Since maintaining seeds for unpopular content entails high bandwidth and administrative costs, this runs counter to the goals of publishers that value BitTorrent as a cheap alternative to a client-server approach. This occurs on a huge scale; measurements have shown that 38% of all new torrents become unavailable within the first month.A strategy adopted by many publishers which significantly increases availability of unpopular content consists of bundling multiple files in a single swarm. More sophisticated solutions have also been proposed; generally, these use cross-torrent mechanisms through which multiple torrents can cooperate to better share content.
Bit Torrent does not offer its users anonymity. It is possible to obtain the IP addresses of all current and possibly previous participants in a swarm from the tracker. This may expose users with insecure systems to attacks. It may also expose users to the risk of being sued, if they are distributing files without permission from the copyright holder(s). However, there are ways to promote anonymity; for example, the One Swarm project layers privacy-preserving sharing mechanisms on top of the original Bit Torrent protocol.
To send or receive files the user must have a BitTorrent client; a computer program that implements the BitTorrent protocol. Some popular BitTorrent clients include Xunlei, Transmission, μTorrent, MediaGet, Vuze and BitComet. BitTorrent trackers provide a list of files available for transfer, and assist in transferring and reconstructing the files. The most well-known BitTorrent tracker is The Pirate Bay.
Programmer Bram Cohen, a former University at Buffalo graduate student in Computer Science, designed the protocol in April 2001 and released the first available version on 2 July 2001, and the final version in 2008. BitTorrent clients are available for a variety of computing platforms and operating systems including an official client released by Bittorrent, Inc.
As of January 2012, BitTorrent is utilized by 150 million active users (according to BitTorrent, Inc.). Based on this figure, the total number of monthly BitTorrent users can be estimated at more than a quarter of a billion
Downloading torrents and sharing files
Users find a torrent of interest, by browsing the web or by other means, download it, and open it with a BitTorrent client. The client connects to the tracker(s) specified in the torrent file, from which it receives a list of peers currently transferring pieces of the file(s) specified in the torrent. The client connects to those peers to obtain the various pieces. If the swarm contains only the initial seeder, the client connects directly to it and begins to request pieces.
Clients incorporate mechanisms to optimize their download and upload rates; for example they download pieces in a random order to increase the opportunity to exchange data, which is only possible if two peers have different pieces of the file.
The effectiveness of this data exchange depends largely on the policies that clients use to determine to whom to send data. Clients may prefer to send data to peers that send data back to them (a tit for tat scheme), which encourages fair trading. But strict policies often result in suboptimal situations, such as when newly joined peers are unable to receive any data because they don't have any pieces yet to trade themselves or when two peers with a good connection between them do not exchange data simply because neither of them takes the initiative. To counter these effects, the official BitTorrent client program uses a mechanism called "optimistic unchoking", whereby the client reserves a portion of its available bandwidth for sending pieces to random peers (not necessarily known good partners, so called preferred peers) in hopes of discovering even better partners and to ensure that newcomers get a chance to join the swarm.
Although swarming scales well to tolerate flash crowds for popular content, it is less useful for unpopular content. Peers arriving after the initial rush might find the content unavailable and need to wait for the arrival of a seed in order to complete their downloads. The seed arrival, in turn, may take long to happen (this is termed the seeder promotion problem). Since maintaining seeds for unpopular content entails high bandwidth and administrative costs, this runs counter to the goals of publishers that value BitTorrent as a cheap alternative to a client-server approach. This occurs on a huge scale; measurements have shown that 38% of all new torrents become unavailable within the first month.A strategy adopted by many publishers which significantly increases availability of unpopular content consists of bundling multiple files in a single swarm. More sophisticated solutions have also been proposed; generally, these use cross-torrent mechanisms through which multiple torrents can cooperate to better share content.
Bit Torrent does not offer its users anonymity. It is possible to obtain the IP addresses of all current and possibly previous participants in a swarm from the tracker. This may expose users with insecure systems to attacks. It may also expose users to the risk of being sued, if they are distributing files without permission from the copyright holder(s). However, there are ways to promote anonymity; for example, the One Swarm project layers privacy-preserving sharing mechanisms on top of the original Bit Torrent protocol.
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