What is the function of the physical layer of the OSI model?

The Physical Layer of the OSI model establishes the physical characteristics of the network (e.g., the type of cable, connectors, length of cable, etc.) It also defines the electrical characteristics of the signals used to transmit the data (e.g. signal voltage swing, duration of voltages, etc.). The Physical Layer transmits the binary data (bits) as electrical or optical signals depending on the medium.