Advances in MEMS technology, wireless communications, and digital electronics have enabled the development of low-cost, low-power, multifunctional sensor nodes that integrating the ability of sensing, computing, and communication. The low per node cost will enable the development of densely distributed sensornet for a wide range of applications. Sensornet is usually deployed in remote and hostile area without human care. To achieve scalable, robust and long-lived goal, sensornet itself should execute adaptive adjustment and burn energy economically. In this paper we present the idea of context aware sensornet (CASN). Be context aware, sensor nodes are expected to use contexts available and adjust their behaviors correspondingly. Also, cooperative sensor nodes are expected to use context to promote their collaboration. The paper presents the motivation and research challenge of building CASN. It also briefly discusses the implementation issues of CASN middleware. Categories and Subject...