How does the Internet work? - The Tao of Computing - page 296

Despite the complexity, however, millions of people receive
email, use Web browsers to find information, move files via FTP,
and generally utilize the Internet for a wide range of communications
each and every day. This chapter addresses how such communication
is possible—even with the Internet's inherent intricacies. First, we'll
consider matters of organization. How do various pieces fit together
in a way that allows machines to get information from one place to
another? We'll then discuss questions of Internet ownership and ac
cess: who owns what parts of the Internet and how funding is gener
ated to pay for this infrastructure. Once we've covered these basics,
the chapter addresses common questions about experiences you may
have in using the Internet, such as how a browser works and the role
of standards. Let's begin with the organization of the Internet.
How is the Internet organized?
Although you may think of the Internet as a single logical entity,
a more accurate image would involve a confederation of cooperat
ing local, regional, and national networks. To understand this struc
ture, some history may be helpful.
In the 1960s, most computing was done on large computers,
called mainframes . Mainframes were not quite the portable and
userfriendly personal computers that we know today; rather, they
were large, heavy machines that were usually operated by experi
enced technicians. In many cases, these machines worked by them
selves or in clusters that were physically close to each other. When
connections between distant machines were needed, companies used
telephone lines to dial up from one location to another. After estab
lishing a connection between locations, the computers used these
dialup lines for communication. When greater capacity, or band-
width, was needed for communications, companies sometimes
leased telephone lines from one location to another. By leasing a
telephone line, a company made an exclusive physical wire connec
tion with a different location, and no longer needed to dial up their
telephone box. Leased lines also could be somewhat more reliable
than depending upon a dialup telephone. Both dialup and leased
lines worked reasonably well, as long as volume was relatively low
and one machine always communicated with just a few others.
Then, in 1969, for various practical and strategic reasons, the
U.S. Department of Defense (DoD) established an experimental net