AHTM: Achieving efficient flow table utilization in Software Defined Networks

In Software Defined Networks (SDN), more packet fields are included to design fine-grained policies. These policies are stored as entries in switch Flow Table. However, fine-grained policies cause the scalability issue as a single flow entry needs larger storage space and a significant number of flow entries need to be stored, but the Flow Table is limited due to the constraints of Ternary Content Addressable Memory (TCAM). To address this issue, we propose Adaptive Hard Timeout Method (AHTM) to improve the Flow Table utilization by optimizing the timeouts of flow entries, thus the Flow Table is reused efficiently. AHTM models the Flow Table as a queueing system and derives closed-form formulas for analysis and optimization. We also implement AHTM as a light-weighted SDN application and it offers interfaces to other applications. The simulation results show that AHTM can achieve the balance between blocking probability and extra workload to SDN controller.