Physical Layer (Layer 1)
The physical layer of the OSI model identifies the physical characteristics of the network, including the following specifications:
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Hardware The type of media used on the network such as type of cable, type of connector, and pinout format for cables.
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Topology The physical layer identifies the topology to be used in the network. Common topologies include ring, mesh, star, and bus.
In addition to these, the physical layer also defines the voltage used on a given media and the frequency at which the signals that carry the data move from one state to another. These characteristics dictate the speed and bandwidth of a given media as well as the maximum distance over which a certain media type can be used.