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 the following diagram:
FlowVisor as a network slicer
FlowVisor creates rich slices of network resources and delegates control of each slice to a different controller and also promotes isolation between slices. FlowVisor, originally developed at Stanford...