Towards Minimizing Average Finish Time of P2P File Delivery Under Peer Leaving

Optimized Water Filling scheduling (OWF) has been studied previously \cite{p2p:Ezovski2009} for no peer leaving Peer-to-Peer (P2P) network, where the problem of efficiently delivering a common set of data from a single base station to multiple users that have heterogeneous uploading capacity was examined. In the absence of peer leaving, it has been demonstrated that OWF can achieve significant performance improvement by exploiting the optimal tradeoff between augment of last finish time and reduction of average finish time. However, peer leaving is a typical behavior of P2P file sharing network, and minimizing average finish time combined with the effects of peer leaving necessitates a more complex scheduling policy. In this work, we extend their studies to P2P networks with users are subject to leave when they complete the data gathering. A simple scheduling method, named reversed water filling method (RWF) is proposed to adapt problem of peer leaving. We also examine the finish time and total network access time of peers under different file distribution strategies. The results show that RWF method yields significant shorter average finish time and total network access time than its predecessors and all other known file delivery methods under peer leaving condition. The results provide fundamental insights of scheduling for improving performance of P2P systems.