LOFT: A latency-oriented fault tolerant transport protocol for wireless sensor-actuator networks

Wireless sensor-actuator networks, or WSANs, refer to a group of sensors and actuators which collect data from the environment and perform application-specific actions in response. To act responsively and accurately, an efficient and reliable data transport protocol is crucial for the sensors to inform the actuators about the environmental events. Unfortunately, the low-power multi-hop communications in WSANs are inherently unreliable; the frequent sensor and link failures as well as the excessive delays due to congestion further aggravate the problem. In this paper, we propose a latency-oriented fault tolerant data transport protocol in WSANs. We argue that reliable data transport in such a real-time system should resist to the transmission failures, and should also consider the importance and freshness of the reported data. We articulate this argument and provide a cross-layer two-step data transport protocol for on-time and fault tolerant data delivery from sensors to actuators. Our protocol adopts smart priority scheduling that differentiates the event data of non-uniform importance. It balances the workload of sensors by checking their queue utilization and copes with node and link failures by an adaptive replication algorithm. We evaluate our protocol through extensive simulations, and the results demonstrate that it achieves the desirable reliability for WSANs.