Optimizing Flow Idle Timer in Reactive SDN

Reactive Software-Defined Networking (SDN) gives us more flexibility than traditional SDN by adding dynamic path definitions on top of data layer programmability driven by SDN controllers. This flexibility is necessary as it allows us to better utilize the limited capacity of flow tables that switches use to house the logic for handling traffic flows. However, it comes with a cost of control packets generated and exchanged between the controller and switch, processing time at the controller for the several types of control packets vying for its attention, and the waiting time at the switch as it awaits instructions by the controller. This may occur several times for a single traffic flow as the rules periodically expire due to each rule’s idle timer and may need to be reinstalled into the flow table. This paper analyzes the delay incoming packets encounter in such a reactive SDN setup; presents a delay formulation based on modeling the system as M/M/1 queues at the controller and the switch; and studies the relationship between the idle timer, average delay, and flow arrival rate.