Distributed SDN controller system

Although within SDN community, the notion of logically centralized network control is well understood and agreed upon, many different approaches exist on how one should deliver such a logically centralized view to multiple distributed controller instances. In this paper, we survey and investigate those approaches. We discovered that we can classify the methods into several design choices that are trending among SDN adopters. Each design choice may influence several SDN issues such as scalability, robustness, consistency, and privacy. Thus, we further analyze the pros and cons of each model regarding these matters. We concluded that each design begets some characteristics. One may excel in resolving one issue but perform poorly in another. We also presented the design choices to build distributed controller that is scalable, robust, consistent and secure.