OSI Model - Physical Layer

Layer 1 - Physical Layer

Physical layer determines the physical and electrical characteristics of network like type of cables, length, and connectors. At the physical layer, data is transmitted onto the medium cables) in the form of bits (ones and zeros). There are number of types of cables that can used for data transmission but the most common are coaxial cable, fiber cable and twisted pair cables. Physical layer determines the voltage level, timings of voltage changes, physical data rates, maximum transmission distance and physical data rates.

Some of the functions of physical layer involve

• Transmits raw bit stream over physical cable
• Establishments and termination of connections to communication medium such as cables.
• Sharing of Communication resources among multiple users
• Conversion of digital data and signal to transmit over network.

Repeater and hubs operate at physical layer. Repeater connects two segments of network cable. It is a device, which receives the signal, regenerates them to proper signal and sends it to all ports. Repeaters require small amount of time to regenerate the signal. A hub is really a multiple port repeater. Like repeater, hubs does not check the traffic, instead it sends all the data to all the ports. Every device connected to hub or hubs has to listen if the device transmit. It receives the data from one device and sends it to another.