Take most of the computers on the planet, join them together start exchanging information and you get the mother of all WAN's, the internet.
It was not always thus, this table shows internet users since 1995.
As you can see if it had been a disease a lot of us would be dead by now. It is important to remember though that a significant number of the worlds' population have no easy access even now.
The internet is more than the world wide web even though most of us spend most of our time on it. There are other ways of exchanging information on the internet. Telnet and Ftp being but two.
An early version
The US Governments Advanced Research Projects Agency (ARPA) in many ways built the first network resembling the modern internet.
ARPA created an early version called imaginetively the ARPANET.
Paul Baran who had written an exhaustive study for the U.S. Air Force that recommended packet switching as a method of making a network highly robust and survivable. Particularly during warfare. As a result of this and others endevours, the first node went live at UCLA on October 29, 1969 on what would be called tday, the "eve" network of today's Internet. I doubt they could forsee where there early network would be in 35 years time.
I have talked about connecting computers into networks and how we can do this here . The actual physical networking of the internet does not matter. Connections can be satellite phone line, network cable or a piece of string being flicked (this would be slow, would need someone at either end to re-encode the data and would only be good over short distances), it doesn't matter. What maters is how the data is split up and moved and the fact that we have all agreed on protocols for doing it. I will start with the (fairly) simple stuff and build up in levels as we add funtions on to our network.
The first thing to understand about the internet and for that matter almost all modern computer networks is that data moves in packets.
A packet is in two parts
The Data part
This is the lump of information that needs to moved from one computer to another it might be part of an image on a web page or a word. Whatever it is it is encoded into binary. Think of the G of google in their image on the search page , if it helps. This would never move in just one packet but hey if it helps, it helps.
The Header Part
The packet also contains some other information as well as my google G. It contains what is called a Header.
The Header contains the information the packet needs to move around a network succesfully. The header is further divided up into parts but I will not talk about all of these by name.
Basically the packet knows based on some of the settings in the header. Where it has come from, where it is going to and how big it is.
The one part of he header I will talk about is called the Check Sum. This tells anything that has to process the packet how big the packet should be and it makes the packet fairly unique.
If the checksum is wrong the packet is corrupt and it is rejected. The checksum also allows the packet to be identified if it has been duplicated by a network error.
The computers that deal with the packets take responsibility for working out what has been sent and what has been recieved. They use TCP/IP to do this. It is important to realise that each packet may well pass through many computers before it gets to its destination computer. Each machine in the chain will look at the packet. If it is not corrupt the computer will send the packet on or "route" it towards it destination.
This is really two protocols but they ted to get linked together. Without these there would be no internet.
The TCP part (Transmission Control Protocol)
is the protocol by which the packets move between computers. TCP does a few things for you
- It makes sure the packets go in order so they are not mixed up at the other end.
- It Makes sure corrupt packets go in the bin.
- It makes sure duplicate packets go in the bin
TCP uses the check sum from the packets header for the binning operations.