Physical layer

The shapes and properties of the electrical connectors, the frequencies to transmit on, the line code to use and similar low-level parameters, are specified by the physical layer.

Historically, the OSI model is closely associated with internetworking, such as the Internet protocol suite and Ethernet, which were developed in the same era, along similar lines, though with somewhat different abstractions.

Beyond internetworking, the OSI abstraction can be brought to bear on all forms of device interconnection in data communications and computational electronics.

The bitstream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a transmission medium.

[3] It is a fundamental layer underlying the higher level functions in a network, and can be implemented through a great number of different hardware technologies with widely varying characteristics.

Line coding is used to convert data into a pattern of electrical fluctuations which may be modulated onto a carrier wave or infrared light.

Sharing of the transmission medium among multiple network participants can be handled by simple circuit switching or multiplexing.

Modular transceivers for fiber-optic communication (like the SFP family) complement a PHY chip and form the PMD sublayer.