What is .......... Ethernet?

What is it.

Computers often need to be networked so you want the network cables, plugs, network cards and so on, to all work together.

The plugs must fit in the sockets, the cable must behave the same way no matter who you buy it from. You should be able to purchase network cards from one supplier and know that they will work with cards from another supplier.

For this to happen, manufacturers must use a common standard. And the standard most often used is called 'Ethernet'.

So Ethernet is a standard *partly* designed to allow network hardware to work together.

The official name for Ethernet is the hard-to-remember IEEE802.3 which refers to the American standards body that made it official.

It is one thing for the hardware to physically work together, but then the way data is handled also has to be agreed between the networked computers. And once again Ethernet comes in handy, because it not only defines hardware, it also defines how data is to be handled.

So in a nutshell, Ethernet is a standard that defines network hardware and also how data is to be handled.

Speed

Ethernet has been around for a long time, starting in the 1970's with slow networks running at 10 Megabits per second. Then some years later 100 Megabits per second became practical.

Higher speed is better because you wait around less for data. But then again higher speed often means higher cost for the hardware, so it is a balance.

An Ethernet standard has defined the kind of cable and network cards you need to work at the higher speeds.

Moving on to today 1 Gigabit / sec is becoming common, once again with the right hardware being specified by the Ethernet standard.

It is great to be able to shift a 4.7 GB DVD film across a 1 Gb/sec network in a few seconds, but then the hardware and cables are more expensive than the much slower 0.1Gb/s i.e. 100 Mb/s.

So which one you go for depends on the kind of data you want to move across the network.

Sorting out collisions.

Ethernet then goes on to describe how to deal with data 'collisions'.

For example, say computer A and computer B are both trying to send data at *exactly* the same time i.e. within a few millionths of a second of each other.

The Ethernet standard protocol goes like this:

1. Collision detected
2. Computer A and B to stop sending immediately
3. Computer A to re-send a small random time later
4. Computer B also to re-send a small random time later

The chance that both Computer A and Computer B pick exactly the same random time is quite low. Collision avoided.

A manufacturer of network cards would read this protocol and build this behaviour into his product. Another supplier would do the same, so both products deal with collisions in the same way.

Addressing

Ethernet standard also specifies how data gets to its correct destination. It does this by defining the make-up an ethernet data packet.

The packet includes the destination address. Every network card has an unique address (called the MAC address).

The network card on every connected computer examines the data packet and if the destination address inside the packet matches its MAC address, it is allowed to pass into the computer, otherwise the packet is ignored.

Linking to other standards.

There is a well-accepted information model called the OSI model.

The OSI model describes how data flows from the screen of one user, down through the computer, across the network cable and back up into another person's screen.

The model is split up into a number of abstract layers. Each layer has a name to reflect  its purpose.

Ethernet deals with the Physical and Transport layers of this model. The PHYSICAL layer deals with hardware and the TRANSPORT layer of the model deals with the handling of data across a network.

And the future?

Ethernet has proven so successful over the years that it will continue to be used in the future. At the moment, people are busy putting together an Ethernet standard that can deal with 100 Gigabits per second.

This will be needed because it will become common for very high speed data such as high-definition television signals to be networked around the home.