An underlay for sensor networks: localized protocols for maintenance and usage

We propose localized and decentralized protocols to construct and maintain an underlay for sensor networks. An underlay lies in between overlay operations (e.g., data indexing, multicast, etc.) and the sensor network itself. Specifically, an underlay bridges the gap between (a) the unreliability of sensor nodes and communication and availability of only approximate location knowledge, and (b) the maintenance of a virtual geography-based naming structure that is required by several overlay operations. Our underlay creates a coarse naming scheme based on approximate location knowledge, and then maintains it in an efficient and scalable manner. The underlay naming can be used to specify arbitrary regions. The overlay operations that can be executed on the underlay include routing, aggregation, multicast, data indexing, etc. These overlay operations could be region-based. The proposed underlay maintenance protocols are robust, localized (hence scalable), energy and message efficient, have low convergence times, and provide tuning knobs to trade convergence time with overhead and with underlay uniformity. The maintenance protocols are mathematically analyzed by characterizing them as differential equation systems. We present microbenchmark results from a NesC implementation, and results from a large-scale simulation of a Java implementation. The latter experiments also show how routing using the underlay would perform