Modeling and application of moderate prefetching strategy based on video slicing for P2P VoD systems

In peer-to-peer (P2P) video-on-demand (VoD) streaming systems, each peer contributes a fixed amount of hard disk storage (usually 2 GB) to store viewed videos and then uploads them to other requesting peers. However, the daily hits (namely popularity) of different segments of a video is highly diverse, which means that taking the whole video as the basic storage unit may lead to redundancy of unpopular segment replicas and scarcity of popular segment replicas in the P2P storage network. To address this issue, we propose a video slicing mechanism (VSM) in which the whole video is sliced into small blocks (20 MB, for instance). Under VSM, peers can moderately remove unpopular blocks from and accordingly add popular ones into their contributed hard disk storage, which increases the usage of peers' contributed resource (storage and bandwidth). To reasonably assign bandwidth among peers with different download capacity, we propose a moderate prefetching strategy (MPS) based on VSM. Under MPS, when the amount of prefetched content reaches the predefined threshold, peers immediately stop prefetching video content and then release occupied bandwidth for others. A stochastic model is established to analyze the performance of the MPS and it is found that perfect playback continuity can be got under MPS. Then the MPS is applied to PPLive VoD system (one of the largest P2P VoD systems in China) and measurement results demonstrate that low server load and perfect user satisfaction can be achieved. Also, the server bandwidth contribution of PPLive VoD system under MPS (namely 5%) is much lower than that of UUSee VoD system (namely 30%).