physical layer (OSI) (PL)
The physical layer, layer 1 in the OSI reference model, defines the electronic, functional and procedural parameters and utilities for the physical connection between units on a network.
Functions of the physical layer
The most important functions of the physical layer are connection establishment, maintenance of a physical connection, and connection termination. In particular, it deals with bit transmission, the structure of bits, the meaning of bits, and the methods used to transmit individual bits. The standards relevant to LANs also include the transmission medium, data connectors, amplifier levels, etc. The characteristics of the physical layer depend on the corresponding local network. One example is the Ethernet physical layer.
Services of the physical layer
The provision of the physical connection and the transparent transport of data units can be mentioned as services for the higher layers.
In the case of large data transmission distances, transmission errors caused by the quality of the transmission medium or caused by the atmosphere may occur. These may have a negative effect on the waveform of the signal to be transmitted or on the entire bit unit. Such errors can be eliminated by suitable assemblies - amplifiers, regenerators. If errors cannot be eliminated without affecting the communication of the next layer above (e.g. line failure for a longer period of time, strong electromagnetic interference, etc.), it is a service of the physical layer to pass on error information to it.
The specification according to DIN is: "The physical layer provides unsecured system connections between systems for the transmission of bits".