ee SO this concept is orthogonal to that of applications in the tight hierarchy of OSI protocol layers. The SDN application interfaces with the controller, using it to set proactive flows on the devices and to receive packets that have been forwarded to the controller. Proactive flows are established by the application; typically, the application will set these flows when the application starts up, and the flows will persist until some configuration change is made. This kind of proactive flow is known as a static flow. Another kind of proactive flow is where the controller decides to modify a flow based on the traffic load currently being driven through a network device (Lau, Rubin, Smith, et al. 2000). In addition to flows defined proactively by the application, some flows are defined in response to a Packet forwarded to the controller. Upon receipt of incoming packets that have been forwarded to the controller, the SDN application will instruct the controller as to how to respond to the packet and, if appropriate, will establish new flows on the device in order to allow that device to respond locally the next time it sees a packet belonging to that flow. Such flows are called reactive flows. In this way, it is now possible to write software applications that implement forwarding, routing, overlay, multipath, and access control functions, among others. Some reactive flows act or are modified as a result of stimuli from sources other than packets from the controller. For example, the controller can insert flows reactively in response to other data sources such as intrusion detection systems (IDS) or the Net Flow traffic analyser. The Open Flow protocol act as the means of communication between the controller and the device (Alsulaiman, Alyahya, Alkharboush, Alghafis, 2009; Su, Huang, Hu, 2013; Tootoonchian and Ganjali, 2010). Though Open Flow is the defined standard for such communication in Open SDN Downloaded: 4/15/2022 9:44:49 AM Nova Southeastern University IP Address: 137.52.76.29 Analysis of Issues in SDN S