Ethernet: A Beginner’s Introduction
It didn’t take very long after computers were invented before scientists
realized that they could do amazing and useful things by connecting two
or more of them together and letting them send messages to each other.
That way, they could share their work, or they could share their
printers, they could share disk drives and other resources. They’ve used
a lot of different technologies to let computers send messages to each
other. Computers send messages on light waves and radio waves and
infrared beams and on all kinds of wires. Fat cables and skinny cables,
ribbon cables, telephone cables, and modems with cables. But in the
mid-1970’s a very clever guy by the name of Bob Metcalf invented the
most elegant and popular method of all: he called it “Ethernet.”
Ethernet has evolved through a lot of different versions, and some of them are very sophisticated now. There are people whose entire careers are built on making Ethernet go faster, and they study the molecules and the magnetic waves of the cables.
But if we summarize it at its simplest, original basis, Ethernet is easy to understand, and old style Ethernet used to look like this...
A coaxial cable or wire with little taps on the ends and throughout the middles that could stretch through one or two or three computers: 3 taps, as you see here, or more.
This wire, all coiled up neatly, could be stretched out to about thirty feet in length and it consists of what we would call a “three-node Ethernet segment,” or an Ethernet segment with three taps on it- (one, two and three) which would allow as many as three different computers to be networked at high speed over a relatively short distance. Ethernet has evolved a lot over the years and a more modern Ethernet cable looks like this:
(This one of course would accommodate only two connections, or two computers talking to each other).
To understand the basics of Ethernet, you need to be introduced to three simple concepts:
First, using a very simple analogy, I will illustrate the way one computer can send one bit of information to another computer.
Secondly, we’ll discuss how computers use addressing information to identify each other on a network.
And third, we’ll discuss the way computers take turns in an orderly fashion when transmitting on a network to avoid interfering with one another.