Ethernet

Ethernet is the most common LAN (Local Area Network) technology in use today.

Ethernet was developed by Xerox in the 1970s, and became popular after Digital Equipment Corporation and Intel joined Xerox in developing the Ethernet standard in 1980.

Ethernet was officially accepted as IEEE standard 802.3 in 1985.

The original Xerox Ethernet operated at 3Mbps. Ethernet networks up to 10Gbps now exist.

Ethernet Cabling

The first Ethernet standard, 10Base-5, ran over thick coaxial cable. A later standard, Ethernet 10Base-2, ran over a much thinner coaxial cable. These two versions of Ethernet were colloquially known as thicknet and thinnet.

Modern Ethernet standards run on UTP (Unshielded Twisted Pair) or fiber-optic cabling.

Ethernet Standard	Cable Specification
10Base-T	Category 3 UTP
100Base-TX	Category 5 UTP
1000Base-T	Cat 5e UTP
1000Base-SX	Optical Fiber

Ethernet Topologies

Ethernet 10Base-5 and 10Base-2 used a bus topology. Bus topologies were difficult to maintain and troubleshoot.

Modern Ethernet networks use a star topology with an Ethernet hub, switch, or router at the center of the star.

It is still possible to create a two-node Ethernet network in a bus topology using a null-Ethernet cable between the two devices.

Ethernet DTE and DCE

All nodes on an Ethernet network are either DTE (Data Terminal Equipment) or DCE (Data Communications Equipment).

Ethernet DTE are devices such as computers and printers which are trying to communicate on the Ethernet network.

Ethernet DCE are devices such as switches and routers which are trying to help other devices communicate on the Ethernet network.

Ethernet CSMA/CD

Like any network, Ethernet must have an algorithm for determining when each network node is allowed to communicate.

In Ethernet, this algorithm is known as CSMA/CD (Carrier Sense Multiple Access / Collision Detection).

CSMA/CD has proven to be a very capable, if highly anarchistic, algorithm.