A typical wireless sensor network performs only one action: sensing the
environment. Our requirement for intelligent interaction with the
environment has led to the emergence of Wireless Sensor and Actor Networks
(WSANs), where a group of sensors, actors and a central coordination
entity (sink) linked by wireless medium perform distributed sensing and
acting tasks.
In WSANs, the sensors monitor the environment based on which the sink
issues commands to the actors to act on the environment. In order to
provide tight coupling between sensing and acting, an effective coordination
mechanism is required among sensors and actors. In this context, we identify the
problem of “hazards”, which is the out-of-order execution of queries and
commands due to a lack of coordination between sensors and actors. We
identify three types of hazards and describe the undesirable consequences of
these hazards. In this context, we discuss the basic design needed to
address this problem efficiently. Through simulations we study the performance of the
proposed solution and two basic strategies, and show that the proposed
solution is efficient for a variety of network conditions.