Appendix A: What is the Internet?
The Internet is a decentralized network of networks. What does
that mean? In computer terms, a network is a series of computers
that are connected together to share information or resources.
The Internet connects a variety of sites in a shared network.
These sites may be universities, schools, government, and/or businesses.
While these institutions are not directly connected to one another,
they are electronically connected, which allows them to send information
to one another. The Internet makes physical location much less
important today than it once was. For example, students in Iowa
can use the Internet to reference the Library of Congress right
from their Iowa classroom, without going to Washington, DC. Moreover,
the parents of a student at the local elementary school can receive
information about homework from their child's teacher, without
going to the school.
One of the great strengths of the Internet is its flexibility.
Users can connect to the Internet through a single computer, through
the local area network (LAN) in a single building, or through
the wide area network (WAN) that connects the computers within
a wider region (e.g., all of the computers in a school district).
If the Internet connection is established through a LAN or WAN,
then individual computers within that network will probably be
routed through a main server that connects the network to the
outside world. This routing creates efficiency, as the traffic
from the numerous computers on the local network is organized
and prioritized to make efficient use of the single connection
to the Internet.
With a system as massive as the Internet, it would seem that
there should be some central control governing computers and network
traffic. As mentioned above, the network is almost entirely decentralized.
There are no huge central computers controlling the Internet and
monitoring its activity. Instead, the central core of the Internet
consists of routers, which serve essentially the same function
as postal sorting facilities: they read a recipient address (each
computer has a unique address) and forward information along to
another router that is closer to that address. Eventually, the
"information package" gets to its destination.
While this system may sound inefficient, it works. An e-mail
message may travel through 20 different routers on its way from
the sender to the receiver, but the entire process actually takes
only a second or two. The network is designed this way for a number
of reasons, the most important of which is its high resistance
to damage, even in times of war (the original network was designed
by the military). If one router is destroyed, breaks, loses power,
or otherwise ceases to function properly, traffic is simply rerouted
around the hole in the network.
The Internet is also "interoperable" and "platform independent."
Users of all different kinds of computers can view content, send
information, and receive data on the Internet. E-mail sent from
a Macintosh computer can be received and viewed on another Macintosh—or
on a Windows PC, a Linux computer, or a UNIX machine. That means
when web pages are written in one or more of a shared set of languages,
the language(s) are interpreted almost identically on a variety
of platforms.1
How Does the Internet Work?
The Internet is often referred to as the information superhighway,
which is a useful metaphor to explain how the Internet actually functions.
One should think of the Internet as a superhighway that stretches
around the world. On this superhighway, huge amounts of data are constantly
traveling back and forth, as people request and send information from
the many remote locations connected to the Internet.
In addition, there are numerous smaller information highways
connected to the superhighway, like local routes that connect
to the interstate. For example, if a person drives from Boston,
Massachusetts, to Denver, Colorado, he or she would take a local
road in Boston to the interstate highway; once in the Denver area,
he or she would exit the interstate to a local road leading directly
into Denver.
When an e-mail message travels along the Internet from a computer
in Boston to a computer in Denver, what actually happens to it?
The e-mail application (e.g., Outlookİ, Pegasusİ, etc.) will first
attach a header to the e-mail message. The header is like an address
on the outside of an envelope; it does not change the substance
of the message, but it tells the delivery service (in the case
of e-mail, the Internet) where the message needs to go.
When a user clicks on the send button of the e-mail application,
a router receives the message and sends it on the local highway
toward the superhighway. When the message gets to the superhighway,
passing through a series of smaller highways on the way, another
router directs it the right way. When it gets to the "off-ramp,"
another router intercepts it and directs it further along the
way. Eventually, the e-mail reaches the server of the intended
recipient and waits to be read in an electronic mailbox.
In reality, the Internet does not actually send the entire e-mail
message as one package. Instead, it breaks the message up into a
series of small packets, addresses them, and sends each of them
individually. Each of these packets consists of a header and a little
piece of the message. A single e-mail message may be broken up into
a half dozen individual packets, which are separately routed. They
may take slightly different paths to get to Denver, but once they
are all there, the server at the receiving end reads the address
in the header and puts the pieces back together. The recipient would
never know it had been taken apart. (See appendix
G, "Follow that Packet: Deep Down Security.")
Internet traffic does not consist only of e-mail. In fact, most
Internet users browse the web for public files containing everything
from pictures and small items of information to entire books.
Web traffic is a big part of the total Internet traffic. When
using a web browser, such as Internet Explorer? or Netscape, information
is retrieved from the Internet to be viewed on the user's desktop,
at home or in the classroom. When connecting to a web site, the
browser sends a short message to the site asking it to return
all of the content for the page requested. The computer hosting
the web site receives that message and returns a copy of the web
page. When clicking on a link to another web site, the back and
forth communication occurs each time.
Sometimes a web page takes a bit of time to "load," or show
up on the screen. This is particularly true with a web page that
has many pictures or symbols, called graphics. A file containing
graphics that are much larger than the average e-mail message
may cause this time lag. Just like e-mail messages, these files
get broken up for the routing process—in the case of some
web pages, they're broken into hundreds or thousands of packets
that need to find their way to the person requesting the page.
There is another speed bump in the information superhighway.
Millions of people are sending e-mails and web requests and are
transferring files at the same time. Each of these "messages"
is broken up into dozens, hundreds, or thousands of smaller packets,
which are sent out over the Internet. At any given instant, literally
hundreds of millions of packets are whizzing down the highway.
Routers all over the world are constantly taking packets in and
sending them out towards other routers closer to the packet's
destination. When too many of these packets are on the Internet,
it slows everything down, just like a speed bump on an ordinary
highway.
All of these packets whizzing back and forth are referred to,
collectively, as network traffic. When there is too much traffic
on any given road, or network, the traffic is rerouted—automatically—to
a different but parallel highway or superhighway in order to bypass
the congestion. The Internet, in fact, is not a single superhighway
as the metaphor implies, but is rather a collection of dozens
of parallel superhighways that provide an even greater capacity
for traffic.
As important as it is to understand how information travels from
one computer to another across the Internet, it is equally important
(if not more so) to understand what happens to the Internet traffic
when it gets closer to home. A basic understanding of how LANs function
(see appendix B) is especially important for
agency policymakers who must make decisions about web development
and technology in general.
Footnote
1 These languages are interpreted almost
identically. Different web browsers on different platforms often
interpret data slightly differently (particularly data that do not
comply with the appropriate standards). This may cause web pages
to appear differently on different computers (or, in some cases,
to not load at all).
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