Computer Networking: The Physical Layer

Very complicated mathematics, physics, and electrical engineering principles are underway to transmit huge amounts of data in a small area at incredible speeds. What I need to know about the physical layer is much more approachable.

The physical layer consists of devices and means of transmitting bits across computer networks. A bit is the smallest representation of data that a computer can understand, it's a 1 or a 0. It doesn't matter whether you're streaming your favorite movie or emailing your boss, you are sending 1's and 0's across the physical layer in the many different layers between you and the server you're interacting with. These are sent across cables through a process called modulation, which a way of varying the voltage of a charge across a cable. This kind of modulation is line coding, allowing devices to allow if an electric charge at a certain state is a 0 and another state is a 1. 

 The most common type of cable is known as twisted pair because it features pairs of copper wires that twist together, and their twisted-pair helps prevent unwanted electromagnetic information from transferring.

The number of pairs in use depends on the transmission technology being used. These cables allow for duplex communication, the concept that information can flow in both directions across the cable. On the other hand, simplex communication is unidirectional. A fax is simplex, but a phone is duplex. Full duplex is when devices can fully communicate with each other at the exact same time. Otherwise, the network might operate as half-duplex, where only 1 device can be communicating at a time.

The final step takes place at the endpoints of the network loops. Twisted pair network cables are terminated with a plug that terminates them. The most common plug is an RJ45 plug.

An RJ-45 Plug can connect to an RJ-45 Network Port, which is directly attached to the devices that make up a computer network. Servers and desktops usually only have 1 or 2 networks. Most ports have 2 small LEDs - the link light and LED light. The link light will be lit when it is properly connected to 2 devices that are powered on. The activity light will flash when data is actively transferred on the cable. 

Today, computer networks are so fast that the activity light just communicates if there are any LEDs. The same LED can be used for both link and activity status. There will always be some troubleshooting data available to you through the portlights. Traditional cable networks are the most common option to connects stuff. ]