An SDN can have some level of logical decentralization, with multiple logical controllers. An interesting type of proxy controller, called FlowVisor, can be utilized to add a level of network virtualization to OpenFlow networks and allow multiple controllers to simultaneously control overlapping sets of physical switches. Initially developed to allow experimental research to be conducted on deployed networks alongside production traffic, it also facilitates and demonstrates the ease of deploying new services in SDN environments. FlowVisor can be considered as a special purpose OpenFlow controller that acts as a transparent proxy between OpenFlow switches on one side and multiple OpenFlow controllers on the other side, as depicted in ...
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