STAR: Preventing flow-table overflow in software-defined networks

The emerging Software-Defined Networking (SDN) enables network innovation and flexible control for network operations. A key component of SDN is the flow table at each switch, which stores flow entries that define how to process the received flows. In a network that has a large number of active flows, flow tables at switches can be easily overflowed, which could cause blocking of new flows or eviction of entries of some active flows. The eviction of active flow entries, however, can severely degrade the network performance and overload the SDN controller. In this paper, we propose SofTware-defined Adaptive Routing (STAR), an online routing scheme that efficiently utilizes limited flow-table resources to maximize network performance. In particular, STAR detects real-time flow-table utilization of each switch, intelligently evicts expired flow entries when needed to accommodate new flows, and selects routing paths for new flows based on flow-table utilizations of switches across the network. Simulation results based on the Spanish backbone network show that, STAR outperforms existing schemes by decreasing the controller's workload for routing new flows by about 87%, reducing packet delay by 49%, and increasing average throughput by 123% on average when the flow-table resource is scarce.