Users launch it by clicking on a hyperlink to the file they wish to download, and are given a standard “Save As” dialog, followed by a download progress dialog which is mostly notable for having an upload rate in addition to a download rate. 1.1 BitTorrent Interface BitTorrent’s interface is almost the simplest possible. We will explain how BitTorrent solves all of these problems well. In practice it’s very difficult to keep peer download rates from sometimes dropping to zero by chance, much less make upload and download rates be correlated. The strategy for allocating upload which seems most likely to make peers happy with their download rates is to make each peer’s download rate be proportional to their upload rate. The total download rate across all downloaders must, of mathematical necessity, be equal to the total upload rate. Finally, there is a general problem of fairness. Peers rarely connect for more than a few hours, and frequently for only a few minutes. In addition, real deployments experience very high churn rates. 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. It has not been previously deployed on a large scale because the logistical and robustness problems are quite difficult. Researchers have attempted to find practical techniqes to do this before. 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.
With BitTorrent, when multiple people are downloading the same file at the same time, they upload pieces of the file to each other. 1 What BitTorrent Does When a file is made available using HTTP, all upload cost is placed on the hosting machine. We explain what BitTorrent does, and how economic methods are used to achieve that goal. It achieves a higher level of robustness and resource utilization than any currently known cooperative technique. Abstract: The BitTorrent file distribution system uses tit-fortat as a method of seeking pareto efficiency.
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