What does a northbound API accomplish?

A northbound API enables communication between the SDN controller and higher-level business applications or orchestration systems, facilitating programmatic control and automation of network resources by interacting with the controller's abstracted view of the network.

While related to centralized control, this option is too general and does not specifically highlight the 'programmatic' and 'abstracted network resources' aspects that define a northbound API's role in SDN.

Communication between SDN controllers and physical network devices (switches, routers) is typically handled by southbound APIs (e.g., OpenFlow, NETCONF), not northbound APIs.

This describes a specific application of programmatic control (security applications accessing switches), but it doesn't represent the full scope and fundamental purpose of a northbound API in abstracting network resources for broader programmatic control.