Physical Layer

The first or bottommost layer of the OSI Reference Model is the physical layer. The physical layer is responsible for the physical mechanics of a network connection which include the following:

• The type of interface used on the networking device.

• The type of cable used for connecting devices.

• The connectors used on each end of the cable.

• The pin-outs used for each of the connections on the cable.

The type of interface is commonly called a NIC A NIC can be a physical card that you put into a computer like a 100BaseT Ethernet card or a fixed interface on a switch like a 100BaseTX port on a Cisco Catalyst 1900 series switch. The physical layer is also responsible for how binary information is converted to a physical layer signal. For example if the cable uses copper as a transport medium the physical defines how binary 1 s and 0 s are converted into an electrical signal by using different voltage