In recent years, with the popularization of factory automation and large-scale sensor-actuator networks, networked control systems (NCSs) over optical networks have been attracting considerable research interest. In NCSs, a delay compensator, which includes an average round-trip time (RTT) model, is implemented to improve stability and performance. However, energy-efficient networks based on cyclic sleep techniques can induce rate-dependent fluctuations in the average downstream queuing delay or the average RTT for periodically generated NCS traffic. The fluctuations result in a mismatch between the average RTT model and the actual RTT, which in turn results in destabilization and performance degradation. This letter proposes sleep period randomization methods for energy-efficient Ethernet passive optical networks (EPONs) to prevent rate-dependent fluctuations in the low-rate range. Simulation results are presented to verify the effectiveness of the proposed methods.
