关键词: 计算机网络，P2P TV，网络编码，拓扑优化

Abstract: With network coding(NC) , intermediate nodes can form outgoing packets through coding incoming packets to achieve the theoretically maximum throughput of multicast. Network coding has been applied in P2P TV systems to improve the performance of delivery ratio, delay and so on. Generally, it is simplified in existing P2P TV systems to shorten the waiting time of nodes for incoming data packets and reduce computing overhead. This introduces the impact of the redundancy ratio of data packets on topology, and increases system overhead. The cause of redundancy brought by topology was quantitatively analyzed, and a topology optimization scheme named instant control was proposed to control and optimize topology spontaneously. Experimental results show that instant control reduces redundancy ratio of data packets caused by topology effectively. Compared with other similar work, it achieves better tradeoff between redundancy ratio of data packets and utility ratio of uplink bandwidth capacity, and further reaches higher delivery ratio.

Key words: Computer networks,P2P TV,Network coding,Topology optimization