TimeoutX: An Adaptive Flow Table Management Method in Software Defined Networks

In Software Defined Networks (SDN), applications on the controller could enforce fine-grained control on flows by policies employing more packet fields. These policies are converted to flow entries and stored in switch Flow Table. To store these entries, Flow Table requires large storage space because an entry consisted of more packet fields needs more storage space and the number of entries also increases significantly due to fine-granularity definition of flows. However, Flow Table has limited storage space owing to the constraints of Ternary Content Addressable Memory (TCAM). As a result, the switch Flow Table in SDN faces scalability issue. We address this issue by means of adaptive Flow Table management, namely we manage how long the entries occupy the storage space by setting adaptive timeouts to them. Through this means, the storage space could be reused efficiently and more flows could be supported with the same Flow Table (without updating hardware devices). Our proposed method TimeoutX, for the first time, combines traffic characteristics, flow types and Flow Table utilization ratio to decide the timeout of each entry and it outperforms current timeout setting strategies in both metrics of table miss number and blocked packet number, which indicates TimeoutX could make the best of Flow Table and support more flows.