A controller communicates with applications in the application plane by using ________ ____ such as REST or OSGi.

A controller communicates with applications in the application plane by using ________ ____ such as REST or OSGi.

• A. Southbound API
• B. Northbound API
• C. Eastbound API
• D. Westbound API

Answer: (B)

Interfacing the controller with applications is done through northbound APIs. The controller sits between the application plane and the underlying infrastructure, exposing APIs that apps use to request data, trigger actions, and access services provided by the controller. REST is a common northbound style because it offers simple, interoperable, web-based communication that apps can call over HTTP. OSGi is another mechanism often used in Java environments to expose and discover services within the controller or among apps, enabling dynamic integration. Southbound APIs, in contrast, are used by the controller to talk to network devices or infrastructure elements. Eastbound and westbound terms describe interactions with other controllers or domains, not specifically the application layer. So the option that best fits the description is the northbound API.

Interfacing the controller with applications is done through northbound APIs. The controller sits between the application plane and the underlying infrastructure, exposing APIs that apps use to request data, trigger actions, and access services provided by the controller. REST is a common northbound style because it offers simple, interoperable, web-based communication that apps can call over HTTP. OSGi is another mechanism often used in Java environments to expose and discover services within the controller or among apps, enabling dynamic integration.

Southbound APIs, in contrast, are used by the controller to talk to network devices or infrastructure elements. Eastbound and westbound terms describe interactions with other controllers or domains, not specifically the application layer. So the option that best fits the description is the northbound API.