We propose a flexible and scalable architecture for a network controller platform used for OpenFlow. The OpenFlow technology was proposed as a means for researchers, network service creators, and others to easily design, test, and virtually deploy their innovative ideas in a large network infrastructure, which will accelerate research activities on Future Internet architectures. The technology enables the independent evolution of the network control plane and the data plane. Rather than having programmability within each network node, the separated OpenFlow controller provides network control through pluggable software. Our proposed network controller architecture will enable researchers to use their own software to control their own virtual networks. Flexibility and scalability were achieved by designing the network controller as a modularized and distributed system on a cluster of servers. Testing showed that a group of servers can efficiently cooperate to serve as a scalable OpenFlow controller. Testing using the nationwide JGN2plus network demonstrated that high-definition video can be delivered through OpenFlow-based point-to-point and point-to-multipoint paths.

The deployment of hybrid wide-area OpenFlow networks is essential for the gradual integration of OpenFlow technology into existing wide-area networks. Integration is necessary because it is impractical to replace such wide-area networks with OpenFlow-enabled ones at once. On the other hand, the design, deployment, and operation of such hybrid OpenFlow networks are often conducted intuitively without in-depth technical considerations. In this paper, we systematically discuss the technical aspects of the hybrid architecture for OpenFlow networks based on our experience so far in developing wide-area hybrid OpenFlow networks on JGN2plus and JGN-X, which are nation-wide testbed networks in Japan. We also describe the design and operation of RISE (Research Infrastructure for large-Scale network Experiments) on JGN-X, whose objective is to support a variety of OpenFlow network experiments.