Which layer describes how the data is transmitted over a physical medium?

The layer that describes how data is transmitted over a physical medium is the Physical Layer. It encompasses the hardware technologies and protocols involved in transmitting raw bits over a physical connection, including electrical signals, light signals, and radio waves. This layer defines the characteristics of the physical medium, such as cable types, signal frequencies, and data rates. It serves as the foundation for higher layers in the network architecture, ensuring reliable data transmission.