lications. The controllers communicate with each other using east-west-bound interfaces. SDN networking devices: The SDN networking devices on the infrastructure layer control the forwarding and data processing capabilities of the network. This includes forwarding and processing of the data path. The user plane is composed of data for- warding elements, such as virtual/physical switches and routers, which forward and route the data packets based on the rules prescribed by the SDN controllers. This plane is responsible for all activities related to provisioning and monitoring of the networks. The SDN architecture APIs are often referred to as north-bound and south-bound interfaces, defining the communication between the applications, controllers, and networking systems. A north-bound interface is defined as the connection between the controller and applica- tions, whereas the south-bound interface is the connection between the controller and the physical networking hardware. Since SDN is a virtualized architecture, these elements do not have to be physically co-located. An SDN controller platform typically contains a col- lection of pluggable modules that can perform different network functions such as tracking device inventory within the network along with maintaining information about device capa- bilities, network statistics and analytics, etc. Extensions can be inserted in the SDN control- ler to enhance its functionality in order to support more advanced capabilities such as running algorithms to perform analytics and orchestrating new rules throughout the network. The centralized, programmable SDN environments can easily adjust to the rapidly evolv- ing needs of enterprise networks. The SDN can lower the cost and limit the uneconomi- cal provisioning and can further provide flexibility in the networks. As already mentioned above, SDN and NFV are set to play key roles for operators as they prepare to migrate from 4G to 5G and to gradually scale their networks. NFVO and NFVI, along with SDN, are critical to th