The controller placement problem or the controller selection problem?

In SDN, the control logic of packet processing devices is moved onto the SDN centralized controller. This decoupled networking architecture creates some critical concerns when compared to traditional distributed architectures. One primary concern in this architecture is the placement of the controller, which is commonly known as the CPP. From our extensive literature review, we identify that there is no strict placement rule that best fits every network in SDN. Dynamic addition and deletion of controllers is inevitable. Motivated from this, in this paper, we attempt to transform the CPP into a CSP. We show that, in the dynamic SDN environment, researchers need to pay attention to CSP issues. The clear advantage of CSP over CPP is that, in the dynamic SDN ecosystem, we can answer fundamental questions about the control plane performance, i.e., minimum number of controllers, their workload distribution, and placement/locations. Furthermore, we can meet strict, application-specific, QoS constraints.