What Is Bittorrent?
BitTorrent is a protocol designed for transferring files. It is peer-to-peer in nature, as users connect to each other directly to send and receive portions of the file. However, there is a central server (called a tracker) which coordinates the action of all such peers. The tracker only manages connections, it does not have any knowledge of the contents of the files being distributed, and therefore a large number of users can be supported with relatively limited tracker bandwidth. The key philosophy of BitTorrent is that users should upload (transmit outbound) at the same time they are downloading (receiving inbound.) In this manner, network bandwidth is utilized as efficiently as possible.
What Bittorrent Does?
When a file is made available using HTTP, all upload cost is placed on the hosting machine. With BitTorrent, when multiple people are downloading the same file at the same time, they upload pieces of the file to each other. This redistributes the cost of upload to downloaders, (where it is often not even metered), thus making hosting a file with a potentially unlimited number of downloaders affordable. Researchers have attempted to find practical techniques to do this before. It has not been previously deployed on a large scale because the logistical and robustness problems are quite difficult. Simply figuring out which peers have what parts of the file and where they should be sent is difficult to do without incurring a huge overhead. In addition, real deployments experience very high churn rates. Peers rarely connect for more than a few hours, and frequently for only a few minutes.
Well known economic theories show that systems which are pareto efficient, meaning that no two counter parties can make an exchange and both be happier, tend to have all of the above properties. In computer science terms, seeking Pareto efficiency is a local optimization algorithm in which pairs of counter parties see if they can improve their lot together, and such algorithms tend to lead to global optima. Specifically, if two peers are both getting poor reciprocation for some of the upload they are providing, they can often start uploading to each other instead and both get a better download rate than they had before.
Torrent refers to the small metadata file you receive from the web server (the one that ends in .torrent.) Metadata here means that the file contains information about the data you want to download, not the data itself. This is what is sent to your computer when you click on a download link on a website
Legitimate P2P use is here and has a definite role to play in the future of the Internet. It is without a compromise between the copyright holders and the file sharers, that there will be an ever-escalating arms race of technology versus legal maneuvers. BitTorrent is a nifty program that works in a simple, if counter-intuitive.
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