DHA: Distributed decisions on the switch migration toward a scalable SDN control plane

Distributed control plane is a promising approach to a scalable software-defined networking (SDN). However, traffic changes could incur load imbalance among individual controllers. Live migration of switches from controllers that are overloaded to those that are underutilized may be a solution to handle peak switch traffic using available control resource. Such migration has to be performed with a well-defined mechanism to fully utilize the available resource of controllers. In this paper, we study a scalable control mechanism to decide which switch and where it should be migrated for a balanced control plane, and we define it as switch migration problem (SMP). The main contributions of this paper are as follows. First, we define a SDN model to describe the relation between the controllers and switches from the view of loads. Based on this model, we formulate SMP as a network utility maximization (NUM) problem with the objective of serving more requests under the available control resource. Second, we design a synthesizing distributed algorithm for SMP - distributed hopping algorithm (DHA), by approximating our optimal objective via Log-Sum-Exp function. In such DHA, individual controller performs algorithmic procedure independently. With the solution space F, we prove that the optimal gap caused by approximation is bounded by 1/β log|F|, and the DHA procedure is equal to an implementation of a time-reversible Markov chain process. Finally, the results are corroborated by several numerical simulations.