Distributed multi-controller deployment is a promising method to achieve ascalable and reliable control plane of Software-Defined Networking (SDN).However, it brings a new challenge for balancing loads on the distributedcontrollers as the network traffic dynamically changes. The unbalanced loaddistribution on the controllers will increase response delay for processingflows and reduce the controllers'throughput. Switch migration is an effectiveapproach to solve the problem. However, existing schemes focus only on the loadbalancing performance but ignore migration efficiency, which may result in highmigration costs and unnecessary control overheads. This paper proposesEfficiency-Aware Switch Migration (EASM) to balance the controllers'loads andimprove migration efficiency. We introduce load difference matrix and triggerfactor to measure load balancing on controllers. We also introduce themigration efficiency problem, which considers load balancing rate and migrationcost simultaneously to optimally migrate switches. We propose EASM toefficiently solve to the problem. The simulation results show that EASMoutperforms baseline schemes by reducing the controller response time by about21.9%, improving the controller throughput by 30.4% on average, maintaininggood load balancing rate, low migration costs and migration time, when thenetwork scale changes.
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