22-12-2009, 02:46 PM
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Abstractâ€
The peer-to-peer (P2P) file-sharing applications are becoming increasingly popular and account for more than 70% of the Internetâ„¢s bandwidth usage. Measurement studies show that a typical download of a file can take from minutes up to several hours depending on the level of network congestion or the service capacity fluctuation. In this paper, we consider two major factors that have significant impact on average download time, namely, the spatial heterogeneity of service capacities in different source peers and the temporal fluctuation in service capacity of a single source peer. We point out that the common approach of analyzing the average download time based on average service capacity is fundamentally flawed. We rigorously prove that both spatial heterogeneity and temporal correlations in service capacity increase the average download time in P2P networks and then analyze a simple, distributed algorithm to effectively remove these negative factors, thus minimizing the average download time. We show through analysis and simulations that it outperforms most of other algorithms currently used in practice under various network configurations.
I. INTRODUCTION
Peer-to-peer (P2P) technology is heavily used for content distribution applications. The early model for content distribution is a centralized one, in which the service provider simply sets up a server and every user downloads files from it. In this type of network architecture (server-client), many users have to compete for limited resources in terms of bottleneck bandwidth or processing power of a single server. As a result, each user may receive very poor performance. From a single userâ„¢s perspective, the duration of a download session, or the download time for that individual user is the most often used performance metric. P2P technology tries to solve the issue of scalability by making the system distributed. Each computer (peer) in the network can act as both a server and a client at the same time. When a peer completes downloading some files from the network, it can become a server to service other peers in the network. It is obvious that as time goes on, the service capacity of the entire network will increase due to the increase in the number of servicing peers. With this increasing service capacity, theoretical studies have shown that the average download time for each user in the network is much shorter than that of a centralized network architecture in ideal cases [2], [3]. In other words, users of a P2P network should enjoy much faster downloads.
