The control plane is usually embodied by a central controller, providing a global view of the underlying network situation to the upper application layer. In this chapter, we look into the architecture and performance of the controller in software-defined networks (SDNs) [1] and also provide comparisons of their features. We first review the

Introduction 121 Controllers in SDNs 124

Types of Controllers in SDNs 124 Examples of OpenFlow Controllers 124

Methods to Increase Controller Performance in SDN 125 New Techniques in the Controller of SDNs 126

Drawbacks on Current Available Controllers 126 Controller in an Ethernet-Defined SDN 127

Overview of the Controller in an Ethernet-Defined SDN 127 Partition/Aggregate in Commodity 10-G EthernetNetwork Visualization 127

Controller in WSNs 128 Motivation for WSN Controller Architecture 128

Discussion and Conclusion 130 References 130

framework of SDNs, and then we describe the controller in SDNs. We summarize the new techniques and challenges in recent years for this area, and then we illustrate two areas of implementations: in Ethernet and in wireless sensor networks (WSNs).