A virtual replica node-based flash crowds alleviation method for sensor overlay networks

The rapid development of sensor networks has made it possible to build large-scale sensor overlay networks by integrating separated sensing resources. In our previous work, we employed a range queriable P2P (peer-to-peer) network, Skip Graph, as the overlay substrate of sensor overlay networks. Range queriable P2Ps such as Skip Graph enable retrieving sensing resources whose properties are within the specified range in an effective and scalable manner. A side effect of the range queriable property is that when flash crowds occur, it is likely that multiple nodes with successive keys/IDs will become hotspots at virtually the same time, which rarely happens in typical DHT (Distributed Hash Table)-based systems. In this work, we present a virtual replica node-based approach to protect sensor overlay networks from flash crowds. In the proposed approach, a hotspot node can request physically spare nodes located anywhere in the overlay to generate virtual nodes with its key and force the virtual replica nodes to join the overlay network as if they were normal nodes around the hotspot. The proposed method is effective for both single hotspot and hotspot zone scenarios. With theoretical analysis, simulations, and testbed experiments, we demonstrate that the proposed method is efficient, scalable and feasible.