 OF CONTROLLERS The job of the controller is to instruct the switch as to what action they should perform or take using an interface also known as southbound Application Programming Interface. CBench (2008) mentioned the proximity of controllers to the future needs. As mentioned above, Open Flow is pervasively taking on the SDN market for controllers to communicate with the switches. Now the switches can be either pure or hybrid switches. The function of pure switch is to forward packets straight- forward while the hybrid one supports both features of Open Flow forwarding and traditional switch bridging and routing. Downloaded 4/15/2022 9:44:49 AM Nova Southeastern University IP Address: 137.52.76.29 The Heart and Brain of SDN Uses and Benefits of Controllers Now comes the fun part, WHY use them anyway? What is wrong with the current method? What is the hype all about? Consider Figure 2 and focus on the central part of the image which shows control plane inclusive of agent, logic and driver. Heller, Sherwood and McKeown (2012) clearly mentions that the thing is, if we only have an integrated control and data plane of a router, to make any configuration changes we have to it manually in each and every network centre's routers separately. This is a very tedious and mundane job. To avoid this commotion, Controllers come into play. Once we logically segregate the planes of the routers, controller abstracts the network from the hardware and makes it possible to control the entire network from a single console. They typically contain a collection of "pluggable" modules, meaning they can be detached or attached when the need be, that can perform different network tasks. Some of the basic tasks include gathering network statistics, what all devices are within the network and how to enhance the functionality and support more advanced capabilities such as running algorithms to perform analytics throughout the network. Figure 2. Controller architecture (detailed) SDN Application SDN Application' SDN Application* SDN App Log