In peer-to-peer video-on-demand (VoD) streaming systems, each peer contributes a fixed amount of hard disk storage (usually 2GB) to store viewed videos and then uploads them to requesting peers. However, the daily hits (namely popularity) of different segments of the same 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 network. To address this issue, we propose a video slicing mechanism (VSM) where 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 blocks into their contributed hard disk storage, which increases the usage of peers' storage space. 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 content and then release bandwidth for other peers. We apply the MPS to PPLive VoD system and measurement results demonstrate that low server load and perfect user satisfaction can be achieved.
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