The Effects of Replication on the QoS in P2P VoD Systems

Replication strategy is one of the central design issues in P2P VoD systems. Given the distributed cache spaces of all peers, it aims to address how to utilize them efficiently. In this paper, we concentrate on the essential question for designing: how replication affects the QoS of requests. Unlike the previous works, in order to close to the practice, three types of replicas are differentiated: complete replicas, incomplete replicas and the replicas of viewers in the same channel. The effects of these types are quantified respectively via modeling and simulating. The model of bandwidth competition is presented and it is observed that the QoS of video is not only determined by the Availability to Demand ratio (ATD) of itself, but also influenced by the ATD of the video saved in the same peer. Both theoretical analysis and experiments show that when the viewer size is large enough, the upload capacity of incomplete replicas is equal to that of complete replicas. We argue that proportion replication is not optimal and more replicas should be assigned to the unpopular videos.