We describe the design and implementation of unstructured peer-to-peer networks for large-scale live media streaming through global Internet in this paper. In so called GridMedia system, we adopt gossip-based protocol to organize end nodes into an application layer overlay. Each node in GridMedia independently selects its neighbors and utilizes a novel and efficient push-pull streaming mechanism to fetch data from neighbors with low latency and little redundancy. The traditional pull mode in the unstructured overlay has inherent robustness to high churn rate which is common in peer-to-peer environment while the push mode could efficiently diminish the accumulated latency observed at end users. A practical system based on this architecture has been developed, and we evaluate its performance on PlanetLab [10] in various rigorous conditions. All the results demonstrate that the proposed push-pull method in GridMedia achieves good performance even with high group change rate and very low upload bandwidth limitation. Furthermore, this system was provided for CCTV (the largest TV station in China) to live broadcast the Gala Evening of Spring Festival 2005 over global Internet at the bit rate of 300 Kbps. It is evidenced that more than 500,000 users were attracted all over the world with the peak concurrent online users of 15,239 during the night.
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