PROD: Relayed file retrieving in overlay networks

To share and exchange the files among Internet users, peer-to-peer (P2P) applications build another layer of overlay networks on top of the Internet infrastructure. In P2P file sharing systems, a file request takes two steps. First, a routing message is generated by the client (request initiator) and spread to the overlay network. After the process finishes, the location information of the requested file is returned to the client. In the second step, the client establishes direct connection(s) with the peer(s) who store a copy of that file to start the retrieving process. While numerous research projects have been conducted to design efficient, high-performance routing algorithms, few work concentrated on file retrieving performance. In this paper, we propose a novel and efficient algorithm - PROD to improve the file retrieving performance in DHT based overlay networks. In PROD, when a file or a portion of a file is transferred from a source peer to the client, instead of creating just one direct link between these two peers, we build an application level connection chain. Along the chain, multiple network links are established. Each intermediate peer on this chain uses a store-and-forward mechanism for the data transfer. PROD also introduces a novel topological based strategy to choose these peers and guarantees the transmission delay of each intermediate link is much lower than the direct link. We conducted extensive simulation experiments and the results shown that PROD can greatly reduce the transfer time per file in DHT base P2P systems.