Software-defined Network (SDN) is the promising paradigm for future Internet. It overcomes the weakness of traditional network (TCP/IP), and is considered as an assuring solution to serve a large number of heterogeneous traffic with varying requirements. In order to maintain the changing traffic demands, it encountered with challenges such as maintenance of traffic load, scalability and reliability, security hardening, cross-layer communication. Therefore, it is important to understand, analyze, and enhance the performance, security, and downtime limitations of SDN for implementation, deployment in live network environments and applications. In this book, we analyzed the performance challenges exist in SDN, and designed a controller system model (CSM) which provides energy-efficiency as well as load balancing scheme to address some of the challenges which leads to performance enhancement. This book, therefore provides a new direction to SDN research which enhances the SDN devices performance that most of the Industries currently use. It also helps the professional in computer network research field, or any one else who is interested in network and communication research.