The Basics of an Ethernet LAN

Ethernet is the name of the most commonly used LAN today. A LAN (Local Area Network) is a network of computers that covers a small area like a room, an office, a building or a campus. It is used in contrast with WAN (wide area network) which spans for much larger geographical areas. Ethernet is a network protocol that controls how data is transmitted over a LAN. Technically it is referred to as the IEEE 802.3 protocol.

The protocol has evolved and improved over time and can now deliver at the speed of a gigabit per second. That's one million kbps.

Many people have for their whole lives been using Ethernet without actually knowing it. It is most likely that the wired network in your office, at the bank and even at home is an Ethernet LAN. Besides, most desktop and laptop computers come with integrated an Ethernet card inside so that it is ready to be connected to an Ethernet LAN.

What Do You Need in an Ethernet LAN

To set up a small or big Ethernet LAN, you need the following:

Computers and devices to connect. An Ethernet connects any type of computer to its network as long as the device has an Ethernet adapter or network card.
Network interface cards in the devices. This is either integrated into the motherboard of the computer or installed separately in the device. You also have USB versions of Ethernet cards like external dongles. An Ethernet card is simply known as a network card. It has ports (sort of a socket to which we can connect cables) that can accommodate cables for connection. There are normally two ports, one for an RJ-45 jack (see picture), that connect UTP cables, and one for a coaxial jack.

A hub or gateway to connect your devices in a star network. A hub is a device that acts as a connecting point between devices on a network. It consists of several RJ-45 ports to which you plug the cables.
Cables. UTP (unshielded twisted pair) cables are more commonly used in Ethernet LANs. This is the same type of cable used for landline telephone sets, but fatter, with 8 twisted pairs of wires of different colors inside. The end is crimped with an RJ-45 jack, which is a larger version of the (RJ-11) jacks that plug into your landline phone. When the Ethernet spans beyond a room to distances that reach hundreds or meters, coaxial cable is used. This is the same cable we use for TV, with a round single-core jack.

Software to manage the network. Modern operating systems like recent versions of Windows, Linux and Mac OS are more than sufficient to manage Ethernet LANs. You just need the skills to do do it. There is also third-party software that gives more feature and better control.

How Ethernet Works

It requires quite some knowledge in computer science to understand fully the mechanism behind the Ethernet protocol. But here is a simple explanation for dummies. When a machine on the network wants to send data to another, it senses the carrier (which is the main wire connecting all the devices). If it is free, i.e. no one is sending anything, it sends the data packet on the network, and all other devices check the packet to see whether they are the recipient. The recipient consumes the packet. If there is already a packet on the highway, the device that wants to send holds back for some thousandths of a second to try again until it can send.