A Hybrid Hierarchical Control Plane for Flow-Based Large-Scale Software-Defined Networks

The decoupled architecture and the fine-grained flow-control feature limit the scalability of a flow-based software-defined network (SDN). In order to address this problem, some studies construct a flat control plane architecture; others build a hierarchical control plane architecture to improve the scalability of an SDN. However, the two kinds of structure still have unresolved issues: A flat control plane structure cannot solve the superlinear computational complexity growth of the control plane when the SDN scales to a large size, and the centralized abstracted hierarchical control plane structure brings a path stretch problem. To address these two issues, we propose Orion, a hybrid hierarchical control plane for large-scale networks. Orion can effectively reduce the computational complexity of an SDN control plane by several orders of magnitude. We also design an abstracted hierarchical routing method to solve the path stretch problem. Furthermore, we propose a hierarchical fast reroute method to illustrate how to achieve fast rerouting in the proposed hybrid hierarchical control plane. Orion is implemented to verify the feasibility of the hybrid hierarchical approach. Finally, we verify the effectiveness of Orion from both the theoretical and experimental aspects.