Which of the following layers directly communicates with the physical devices in a network?

The infrastructure layer is the correct choice as it is responsible for managing the physical devices and resources in a network. This layer interacts with the hardware components such as routers, switches, and other networking devices, enabling communication and data transfer at the physical and data link layers of the network model.

In the context of Software Defined Networking (SDN), the infrastructure layer abstracts the physical network elements and provides a programmable interface that allows for the management and configuration of these devices. This abstraction is key to the operational model of SDN, allowing for enhanced flexibility and control over the physical infrastructure while separating the control plane from the data plane.

Other layers mentioned in the options serve different purposes: the application layer is focused on providing network services to end users; the control layer handles network policies and management but does not directly interact with hardware; and the transport layer ensures reliable data transfer between hosts but also does not interact directly with physical devices.