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A File Fetching Method to Reduce the Redundant Traffic on BitTorrent-Like P2P Networks

When dividing a file into many pieces and fetching different pieces from many peers on P2P systems, if the piece is requested from a slow peer whose upload throughput is low, the download time for the whole system may increase because of this slow download. End-game mode, which requests the last piece from all the connected peers at the same time, has been proposed to solve this problem, while the duplicated requests generate redundant traffic. In this paper, we propose a method to avoid requesting a piece from slow peers without the duplicated requests, which can alleviate the increase in download time and generates no redundant traffic. The proposed method and the existing method with end-game mode are evaluated through simulation experiments using BitTorrent as a typical instance of the parallel retrieving method of a file from many peers. As a result, we confirm that our proposal can fetch files in similar length of time as the existing method with end-game mode, with trimming down redundant traffic generated by the existing method, whether or not some peers leave from the network after completion of the file retrieval. We believe that this proposal enhances network assurance absorbing the difference in the peer performance and providing the steady download time without redundancy in traffic.