What describes a northbound REST API for SDN?

A network-element-facing interface is a southbound interface, which communicates from the controller to the network devices, not northbound.

While applications can use SNMP, a northbound API typically uses RESTful principles for network programmability, and is not limited to just SNMP GET requests.

A northbound REST API in SDN is an application-facing interface that allows applications and orchestration systems to program the network and request network services. It uses standard HTTP methods like GET, POST, PUT, and DELETE to interact with the SDN controller, enabling high-level control and automation.

A network-element-facing interface for control and data planes describes southbound interfaces (like OpenFlow), not northbound APIs.