The control layer, sometimes referred to as the SDN controller, serves as the central intelligence of a software-defined network. It provides the abstracted view of the overall network to the application layer, allowing the applications to define network behavior without the need for direct interactions with the networking devices, which are part of the infrastructure layer. The SDN controller makes network-wide decisions based on the policies and the application requirements. Other answers might seem plausible, but they do not accurately define the primary role of the control layer within an SDN environment.