A typical wireless sensor network performs only one action:
sensing the environment. The requirement for intelligent
interaction with the environment has led to the emergence of
Wireless Sensor and Actor Networks (WSANs). 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 show with an
example application, the undesirable consequences of these
hazards. In this context, we discuss the basic design needed to
address this problem efficiently. We propose a distributed and
fully localized hazard-free approach that addresses the
problem based on the design. 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.