Usually, in computer networking and computer architecture, a northbound interface means an interface that lets a specific component communicate with a higher-level component in the same network. A southbound interface is the opposite — it enables a specific component to communicate with a lower-level component.
In software-defined networking, the southbound interface is the OpenFlow protocol specification, which allows communication between the SDN controller and the network nodes.
The northbound interface is protocol-supported communication between the controller and applications or higher-layer control programs.
