The
Internet originated in the late 1960s when the United States developed
ARPAnet - Advanced Research Projects Agency network - a system of
computers able to survive, even if partially, after a bomb attack.
That system was made by a lot of computers connected together, like a web.
That web was divided in LAN - Local Area Networks.
Those
computers were able to communicate with each other even is some of them
were out of service. From that time the Internet is by now world wide,
or WWW - World Wide Web
The protocol that rules all these computers is TCP/IP:
TCP = Transmission Control Protocol
IP = Internet Protocol
The
wonderful characteristic of this protocol is the way it deals with the
information sent and received. The normal phone transmission works in
this way:
From point A directly to point B, using cable or radio
connection. So if something wrong happens to the radio transmitter or to
the cable, the communication is impossible.
With the TCP/IP protocol, on the contrary, the connection from A to B is not direct.
The
information (file) that we want to send is divided in several parts,
packets, and each packet has a bit of the whole information.
Each
packet has a header and a footer, where are store all the indication for
delivery what is being sent (Address, sender, number of the packet).
These
packets follow different paths of the net, passing through different
computers, so even if some of them are not working, the file uses the
ones which are working properly. The computers may be all over the
world. After this trip the file is rebuilt in the right way.
For
instance, if we send a file to a computer that is in a house close to
our office, may be that before arriving to destination, it goes to
Europe and back.
To try to understand just a bit this system, we can do this very simple example:
We
want to send a letter to someone. Instead of sending just one sheet of
paper, we could send 6 sheets. Each one contains 1/6 of the whole
letter.
On the 6 envelopes we write the sender, the address of the
receiving person and the number of the letter (Letter n. 1, letter n.2,
and so on).
Then we can send all this letters, from several Post Office or from just one.
The
person who gets all these letters, has to follows the number on each
letters (1,2, 3...) to be able to read the whole message.
This is good also for safety: if someone gets some letters, he has only part of the message not the whole message.
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