Time-Shifted Streaming in a Tree-Based Peer-to-Peer System

We propose a peer-to-peer (P2P) streaming system that multicasts live video as well as provides the live video as Video-on-Demand (VoD) during the live session. The proposed system allows users to individually pause and resume a live video stream, and to view video that was streamed before the particular user joined the session. Since live video content naturally results in many users watching it online at the same time, the P2P concept is leveraged to reduce server load. We extend our Stanford Peer-to-Peer Multicast (SPPM) protocol, originally designed for live video multicast, to support playback control. To achieve this in a P2P fashion, peers store received video packets in their local buffer and forward them at a later time when requested by other peers, which is called time-shifted streaming. To understand interaction between live and time-shifted traffic, we analyze video availability of the proposed system, which refers to how many peers possess video contents of a particular position. Motivated by the analysis, we propose fast prefetching and a parent selection scheme suitable for fast prefetching in order to further reduce server load by disseminating video quickly. Fast prefetching is possible because the relaxed transfer deadline of time-shifted streams and peers’ extra uplink bandwidths are exploited. With simulations and mathematical analysis, it is shown that fast prefetching not only alleviates the requirement of server bandwidth by expediting video dissemination, but also mitigates video disruption due to peer churn.