What is the function of "off-the-shell" switches in a controller-based network?

Providing a central view of the deployed network is a function of the SDN controller or a network management application, not the data plane switches themselves.

In a controller-based (SDN) network, off-the-shelf or 'data plane' switches are primarily responsible for the high-speed forwarding of packets. They receive forwarding instructions and policies from the central SDN controller and simply execute those rules without making independent routing decisions or policy determinations.

Making routing decisions is the responsibility of the SDN controller, which then programs the forwarding paths into the data plane switches, rather than the switches making these decisions autonomously.

Setting packet-handling policies is a control plane function performed by the SDN controller, which then enforces these policies by pushing rules to the data plane switches.