In-switch Dynamic Flow Aggregation in Software Defined Networks

Abstract

The limited size of the flow table, usually implemented by ternary content addressable memory (TCAM), may result in the flow table overflow problem, which becomes severer in software defined networks (SDN). To conquer this problem, this paper proposes an in-switch dynamic flow aggregation (IDFA) mechanism, which can be dynamically triggered. In the IDFA, redundant flow entries are inserted to speed up flow aggregation convergence time. The uniqueness of the proposed IDFA is that it resides in an OpenFlow switch, instead of acting as an application in an SDN controller, which avoids link delays between the controller and switches. This paper also proposes two novel techniques, degradation and repermutation, to aggregate flows effectively while keeping semantic equivalence. Evaluation results show that, the average compression ratio of the IDFA in a fat-tree topology under a LAN (random IP) environment is 26.3% (43%) better than that of the Flow Table Reduction Scheme (FTRS), a representative related work. The average flow aggregation convergence time of the IDFA in the fat-tree topology is 84% shorter than that of the FTRS. In addition, the occurrence probability of flow table overflow in the fat-tree topology is 26.71% lower than that of the FTRS.