Source: The Free On-line Dictionary of Computing (26 July 2010)
physical layer
layer 1
Layer one, the lowest layer in the OSI seven
layer model. The physical layer encompasses details such as
electrical and mechanical connections to the network,
transmission of binary data as changing voltage levels on
wires or similar concepts on other connectors, and datarates.
The physical layer is used by the data link layer.
Example physical layer protocols are CSMA/CD, token ring
and bus.
(2004-06-29)