App intelligently swaps and stacks tunnel labels in the packets. The top-down procedure finishes when leaf cNodes run their TE and program the physical switches. Summary SDN architecture introduces a separation between the control and forwarding components of the network. Among the use cases of such architecture are the access/aggregation domain of carrier-grade networks, mobile backhaul, data center networks, and cloud infras- tructure, all of which are among the main building blocks of today's network infrastructure. Therefore, proper design, management, and performance optimization of these networks are of great importance. 4 Software-Defined Networks Principles and Applications In this chapter, we first provide an overview of the design principles and building blocks of the SDN architecture. We discuss the use cases, the challenges, and its business impact. Then, we dive into more details of SDN controller and SDN data plane separately. Finally, we conclude with introducing a few interesting and novel applications that SDN enables. SDN and NFV in 5G Mobile network operators are looking for cheaper and more efficient ways to connect subscribers/devices to their networks by search- ing for creative ways to minimize network traffic and latency. Next-generation 5G mobile networks will steer mobile network operators toward software-defined networks (SDN), agnostic net- work access, mobile edge computing, and 5G network slicing where grouped subscribers or machine-to-Machine (M2M) and Internet of things (IoT) devices are serviced by separate, virtualized core networks. Next-generation 5G mobile networks will merge IT and Cloud concepts into mobile core networks methods for accessing subscriber information in order to reduce data latency and network backhaul. Mobile edge computing will position network applications, service applications, and subscriber profiles on the network edge in close proximity to the subscriber/device in order for 5G networks to accomplish their goals, thus making services and profile as mobil