The main mission of the physical layer concerns the physical connection of two units within the same network. It thus allows to establish and terminate the connection, while ensuring that it works correctly during the transfer.
In addition to the transfer itself, the « physical layer » also provides for the bit structure, the meaning of these and the different methods governing their transfer. The data is transferred bit by bit, prepared, reinforced and, if necessary, converted. During the process, the physical layer makes no distinction between payload data and control information, nor does it deal with error correction.
Indeed, the physical layer only activates the physical connection, transfer all relevant data as a bit stream and properly disable the connection once the transfer is complete. The “physical layer” nevertheless supports some management functions.
The physical layer also answers, among other things, the question of the physical representation of the binary digits (1 and 0), which can be, for example, electrical, electromagnetic, optical or acoustic. The physical layer also checks the direction in which the transfer takes place. The properties of individual connectors and cables, pin assignments and physical values (such as current and voltage) are also relevant information for the physical layer.
