Disturbance-observer-based active queue management with time delay using software-defined networking controller

This paper presents an active queue management (AQM) architecture using a software-defined networking (SDN) controller. The SDN controller can achieve the AQM of a router from a remote location. It leads to realizing cooperative AQM of multiple routers and flexible AQM taking traffic conditions of the total network system into account. However, the AQM control system includes additional time-delay elements between the SDN controller and routers, and they have not been discussed. In this research, we discuss the effects of the time-delay elements on the AQM performance. Simulations are performed to compare the queue length variations in a bottleneck router, when we adopt a disturbance-observer (DOB)-based proportional-derivative (PD) controller or a proportional-integral-derivative (PID) controller as an AQM controller. The simulation results show that the DOB-based PD controller tracks the target queue length more accurately than the PID controller even if the additional time-delay elements exist.