Node selection method for P2P (peer to peer) systems

The invention discloses a node selection method for P2P (peer to peer) systems and relates to the technical field of broadcasting application devices and methods directly related to broadcast information or broadcast time and space. The method includes: searching for neighbor nodes the closest to a node, transmitting a UDP (user datagram protocol) message to all neighbor nodes to request for bitmap information, and selecting optima partner nodes according to round-trip transmission time, whether or not data blocks in an emergency window are held and whether or not rare data blocks and bitmap information are held. According to the method, the concept of autonomous domain is disclosed and applied to the discovery of the neighbor nodes, the nodes equal to former ones in terms of geographical position and operator are selected prior as own service nodes, the optimal partner nodes are selected according to the round-trip transmission time, whether or not data blocks in an emergency window are held and whether or not rare data blocks and bitmap information are held, an overlay network is optimized by regularly updating the neighbor nodes and the partner nodes, network downloading speed is increased, video-on-demand system delay is low, and transmission quality of streaming media is guaranteed.