Resolving Controller Load Imbalanced State in Multiple Controllers based Software-Defined Network

This paper proposes a switch migration scheme to balance the load of all controllers in multiple controllers based software-defined network. Several works define the number of requested packets as a controller load. The controller needs to hold the current processing until receiving a response message from the switch before processing a new request. For this reason, the number of requested packets incorporates with the path cost is defined as a controller load. In a multiple controllers approach, a load imbalanced state is recognized if a load of one controller is biased against a load of the other controllers. In the imbalanced state, connections of some switches that belong to a controller with high load are disconnected, and the switches are reconnected to the other controllers with the lower load. This process is called a migration process. The probability of migration and the efficiency of migration are used as a decision to find a switch to be migrated and the other controller to be reconnected. The load imbalanced state is resolved but the aggregate load of all controllers may be increased. In the proposed scheme, the aggregate load of all controllers after the migration is used as an indicator to select the migrated switch and a new controller. A pair of migrated switch and controller with the minimum aggregate load is selected so that the aggregate load is reduced compared to the conventional scheme. Computer simulation result shows that the proposed scheme reduces the aggregate load, compared to the traditional scheme.