Final answer:
An SDN controller uses Southbound APIs to manage and communicate with network devices on the data plane(option b).
Step-by-step explanation:
An SDN controller communicates with devices on the network data plane by utilizing b)Southbound APIs.
Southbound APIs are essential for enabling the SDN controller to manage, configure, and exchange information with network devices such as switches and routers. They provide the mechanism by which the controller can implement its policies across various pieces of network hardware. In contrast, Northbound APIs are used for communication between the SDN controllers and higher-level network services or applications, not for direct device management. Therefore, the correct answer to which interface enables an SDN controller to communicate with the network devices is Southbound APIs.