Optimization of Web Service-Based Control System for Balance Between Network Traffic and Delay

In Internet of Things systems, Web services enable interoperable machine-to-machine communication over networks. Polling mechanism is a practical way for a Web service-based control system to enable its actuator to respond to its controller under uncertain environments where the actuator does not know exactly when the controller updates its command. Fast response demands a high polling frequency (polling mechanism handles the event in time-driven mode) which may lead to heavy network traffic. Therefore, how to make the optimal tradeoff between the network traffic and delay in a Web service-based control system becomes an interesting problem. This paper formulates the problem of finding the optimal polling frequency control policy of a Web service-based control system as a constrained Markov decision process (CMDP). The policy is such that the actuator responds to the controller within a tolerable delay threshold while minimizing network traffic. An algorithm called CMDPA is proposed to solve the problem. Simulation and field experiments show our policy performance.