Reducing Inconsistency between Software-Defined Networking Controllers

In distributed SDN, each controller builds the "global network view" by obtaining missing pieces of global network view from other controllers. All SDN controllers need to maintain consistent view of global network in order to make a correct routing decision. An inconsistent global network view may result in incorrect routing decision a switch. In order to achieve correct routing decision while keeping low latency and high throughput of controller, we need to avoid inter-controller communication overhead at the time of flow setup. In order to do so, we need to make an assignment of switches to controllers such that routing decision on each flow can be made by as small number of controllers as possible. In order to achieve such assignment of switches to controllers, we propose a controller placement model based on traffic locality. We identify a cluster of switches such that fair amount of traffic flow remains inside the cluster and assign the switches belonging to the cluster to the same controller. Thereby the inconsistency between controllers has less impact on the accuracy of controllers routing decision for the traffic flow because the controller is like to have all necessary information on the network resource to calculate the route for the traffic flow. In order to make such clusters of switches, we employ Infinite Relational Model (IRM), a nonparametric Bayesian model that discovers relational structure in data sets as a set of clusters. Simulation results show that our proposed method reduces the inconsistent probability that controllers need to update a global network view.