ARPA intended to establish a communication system that automatically
detects failures of its components and accordingly employs different
paths to transfer packages of data to their destination.
Figure 1
illustrates this idea.
The research supported by the ARPA resulted in a network called
ARPAnet which was first realized with four computers at the University
of California, Los Angeles.
Based on the ARPAnet technology the NSF (National Science
Foundation) set up the NSFnet in the 1980s. Initially, the NSFnet
connected several universities and companies in the USA and was
used for non military purpose.
Later, more and more institutions from all over the world joined the
NSFnet in order to participate at the fast and easy exchange of
information enabled by this technology. This global communication
system is called the Internet.
Nowadays, the Internet consists of more than 2mio computers in more
than 30000 networks. The different networks building up the Internet
are connected by routers which are computers that can establish
connections to computers of other networks than their own. Hence,
via the routers each computer on the Internet can contact any other
computer on the net. A scheme illustrating how the Internet is built up
is shown in
figure 2 .