Research On P2P File Sharing System Based On Fountain Codes

Nowadays, because P2P technology has many advantages such as decentralization, better extendability, high stability and balanced load, it is used in more and more fields including file sharing, instant messaging, distributed computing and cooperative work, and it prompts the emergence of new development and application in these fields. File sharing is always an important momentum for the development of network technology and it is the most typical application of P2P technology. On the other hand, there are some problems existing in file sharing system in general and it is difficult to solve through P2P technology itself, for example, the system is sensitive to the torrent nodes and the network bandwidth utilization is not high.As a practical technology in the field of communications, digital fountain technology has attracted universal attention and research. The rateless characteristic makes it have a good utilization prospect in satellite communications, multimedia broadcasting, wireless communications, and so on. This thesis focuses on the following research:how to improve the encoding and decoding performance and how to apply digital fountain technology to P2P file sharing system.The main tasks of this thesis are listed as follows:1. BitTorrent protocol and its working principle are intensively studied, the open source code of client Enhanced CTorrent is analyzed. The deficiencies and shortcomings of BitTorrent system are pointed out and a detailed analysis of its causes is put forward.2. Digital fountain technology is studied on deep levels, the degree distribution function and decoding algorithm are studied and a large number of simulation experiments of LT codes are carried out, at last, a best encoding and decoding solution for P2P file sharing system is selected.3. On the basis of intensive understanding of digital fountain technology and Enhanced CTorrent client, an improved P2P file sharing system based on digital fountain codes is designed and implemented. The new system solves the existing problems and improves file downloading performance.4. The performance of improved P2P file sharing system is tested, and the reasons for the download performance improvement are analyzed. Experimental results show that the improved P2P file sharing system with digital fountain codes has a good download performance and the system is more robust.