Due to unpredictable peer churns (joins, leaves and failures), it is challenging to offer video continuity in peer-to-peer (P2P) live streaming. In this paper, we study a push-based P2P network formed by unreliable nodes (i.e., nodes which may churn at any time). To achieve high stream continuity, the video is encoded into k MDC (Multiple-Description Coded) streams and t FEC (Forward Error Correction) streams. To achieve low delay and reduce error correlation between streams, the k + t streams are pushed to the nodes in parent-disjoint spanning trees. The issue is how to construct these trees minimizing the worst-case node delay. We address the optimization of the spanning trees through problem analysis and algorithmic design. After presenting a model capturing important system parameters and delay components, we formulate the problem and prove that it is NP-hard. We then propose SUN (Streaming with Unreliable Nodes), a simple, adaptive and distributed algorithm which continuously reduces delay through overlay adaptation. Through extensive simulation on real Internet and Internet-like topologies, we show that stream continuity can be achieved with push-based P2P streaming. SUN is effective, achieving low delay and high continuity in the presence of node churns for P2P live streaming.
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