What is the function of a network controller in SDN architecture?

In Software-Defined Networking (SDN) architecture, the network controller plays a crucial role as the central component responsible for managing network resources and controlling data flow. This centralized controller has a comprehensive view of the entire network, allowing it to make informed decisions about how data packets should be forwarded, routed, and prioritized.

By separating the control plane from the data plane, the network controller can dynamically adjust traffic flows and manage resources based on real-time conditions and policies, which enhances network efficiency and flexibility. It can optimize performance by directing traffic along the most efficient paths or implementing Quality of Service (QoS) policies to ensure that critical applications receive the necessary bandwidth.

The other options provided, while related to networking, do not accurately capture the primary function of a network controller in SDN. Routing traffic to the internet is a task typically associated with routers, not specifically with the SDN controller. Encrypting network data is primarily concerned with security protocols, and monitoring network usage for billing relates more to network management and analytics rather than the core function of resource management and data flow control that the network controller performs.