Effective idle_timeout value for instant messaging in Software Defined Networks

In Software Defined Networks (SDN), each flow table entry is dedicated to an individual flow and has an idle timeout value associated with it. Due to limited flow table and controller processing resources, SDN suffers from scalability problem especially when dealing with a large number of flows. As Instant Messaging (IM) applications usually generate too many different flows and idle timeout has effect on the two limited resources, we try to obtain the effective idle timeout value for IM in this paper. Firstly, based on ON/OFF traffic model, we explore the effect of idle timeout on flow table and controller processing resources respectively, and then we define corresponding costs of the both resources. After that, we derive the lower and upper bounds of idle timeout value considering the constraints of limited flow table and controller processing resources. Furthermore, we formulate an optimization model to calculate the effective idle timeout for IM. At the end of this paper, we note that the simulation results are consistent with our theoretical analysis, which verifies the effectiveness of our model.