The Physical Layer is a fundamental layer upon which all higher level functions in a network are based. However, due to the plethora of available hardware technologies with widely varying characteristics, this is perhaps the most complex layer in the OSI architecture. The implementation of this layer is often termed PHY.
The Physical Layer defines the means of transmitting raw bits rather than logical data packets over a physical link connecting network nodes. The bit stream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a hardware transmission medium. The Physical Layer provides an electrical, mechanical, and procedural interface to the transmission medium. The shapes of the electrical connectors, which frequencies to broadcast on, which modulation scheme to use and similar low-level parameters are specified here.
Source: from Federal Standard 1037C
The Physical Layer is also concerned with
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