OSI Layer 1 – Physical / Physical

The Physical layer of the OSI model is responsible for the transfer of the bits - 1's and 0's that make up all of the computer code.

This layer represents the physical medium that carries traffic between two nodes. An example would be your Ethernet cable or Serial Cable. But don't get too caught up on the word "Physical" - this layer got its name in the 1970s, long before wireless communication in networks was a concept. Thus, WiFi, even though it has no real physical presence, is also considered a Layer 1 protocol.

Simply put, Layer 1 is whatever carries 1's and 0's between two nodes.

The actual format of the data on the "wire" may vary with each medium. In the case of Ethernet, bits are transferred in the form of electrical pulses. In the case of Wifi, the bits are transferred in the form of radio waves. In case of Fiber, the bits are transferred in the form of pulses of light.

Apart from physical cables, Repeaters and Hubs also operate at this layer.

A repeater simply repeats the signal from one medium to another, allowing a series of cables to increase the signal's range so that it can travel beyond the limits of a single cable. This is typically used in large WiFi deployments, where a single WiFi network is "repeated" across multiple access points to cover a larger range.

Hubs are just multi-port repeaters. If four devices are connected to one Hub, anything sent by one device will be repeated to the other three.