Research Of BitTorrent's Principle And Algorithm And Its Performance Optimization

The BT technology is a new peer-to-peer resource sharing technology with the "the connection more, downloading is quicker" feature. Along with the BT technology widespread application, the BT technology has become one of indispensable downloading methods on the Internet. In this paper, BT technology was researched deeply. The speed of BT downloading the document is enhanced. It has the positive practical value.Firstly, in this paper, by analysising BitTorrent client and server source code detailedly, the key principles and core algorithms of BitTorrent was understanded deeply. After analysing and data testing the pieces priority algorithm, we found that the time complex of algorithm has optimizing space. At the same time, some expand protocols especially fast downloading pattern(this pattern has been accepted by the BT official protocol)were analysed deeply.Following that, in allusion to the shortage of the pieces priority algorithm, a optimizing scheme was raised. This scheme reduces the time complex of algorithm, enhances the uniformity of document peers in the system in a certain extent, and as a result improves the speed of downloading documents. Moreover, based on fast downloading pattern, a new pattern named fast downloading pattern based on priority was brought out. This pattern can set and adjust the priority of point in the system dynamic. As a result, the highest priority point can obtain the best BT servers, namely holding fast downloading speed and more points for downloading. This can achieve the policy of "encouragement making seed", then the quantity of seed is increased in the whole system, thus the document downloading speed of the overall system is enhanced greatly.Finally, the optimizing scheme designed by this paper was realized and tested. The result of testing shows that the optimizing pieces priority algorithm has lower time complex than the old one, and it can improve the speed of downloading document in the system effectively. At the same time, the fast downloading pattern based on priority which brought by this paper can improve the downloading speed of the high priority node availably, shorten downloading time. Along with seed quantily increasing, the downloading speed of others nodes is increased. That will achieve the aim of improving the downloading speed of whole system.