Most peer-to-peer content distribution sys- tems require the peers to privilege the welfare of the overall system over greedily maximizing their own utility. When downloading a file broken up into multiple pieces, peers are often asked to pass on some possible download opportunities of common pieces in order to favor rare pieces. This is to avoid the missing piece syndrome, which throttles the download rate of the peer-to-peer system to that of downloading the file straight from the server. In other situations, peers are asked to stay in the system even though they have collected all the file's pieces and have an incentive to leave right away. We propose a mechanism which allows peers to act greedily and yet stabilizes the peer-to-peer content shar- ing system. Our mechanism combines a fountain code at the server to generate innovative new pieces, and a prioritization for the server to deliver pieces only to new peers. While by itself, neither the fountain code nor the prioritization of new peers alone stabilizes the system, we demonstrate that their combination does, through both analytical and numerical evaluation. I. INTRODUCTION
@cite_10 proves the stability of the P2P system when the peers are asked to stay in the system for some time after download completion that depends on the peer arrival process and download rate. As in the previous system, peers are asked to stay longer, either explicitly or by withholding download, in order to stabilize the system.
@cite_10
2015690067
Peer-to-peer (P2P) communication in networks for file distribution and other applications is a powerful multiplier of network utility, due to its ability to exploit parallelism in a distributed way. As new variations are engineered, to provide less impact on service providers and to provide better quality of service, it is important to have a theoretical underpinning, to weigh the effectiveness of various methods for enhancing the service. This paper focuses on the stationary portion of file download in an unstructured P2P network, which typically follows for many hours after a flash crowd initiation. The contribution of the paper is to identify how much help is needed from the seeds, either fixed seeds or peers dwelling in the system after obtaining the complete file, to stabilize the system. It is shown that dominant cause for instability is the missing piece syndrome, whereby one piece becomes very rare in the network. It is shown that very little dwell time is necessary--even if there is very little help from a fixed seed, peers need to dwell on average no longer than it takes to upload one additional piece, after they have obtained a complete collection.