80 Part I • Information Technology
serve a limited audience and other networks like the
Internet that are available to anyone or any organization
that wishes to buy the networking service.
Virtual Private Networks. A virtual private
network(VPN) provides the equivalent of a private
packet-switched network (as discussed in the previous
section) using the public Internet. VPN data transmission
rates vary from a low 56 kbps up to a very high 40 gbps, all
at a very reasonable cost compared to other alternatives,
but the network’s reliability is low. To establish a VPN, the
user organization places a VPN gateway (a special router
or switch) on each Internet access circuit to provide access
from the organization’s networks to the VPN. Of course,
the user organization must pay for the access circuits and
the Internet service provider (ISP). The VPN gateways
enable the creation of VPN tunnelsthrough the Internet.
Through the use of encapsulation and encryption, these
tunnels ensure that only authorized users can access the
VPN. The advantages of VPNs are low cost and flexibility,
while the primary disadvantage is low reliability. An
organization can create a VPN itself, or it can contract with
a vendor such as AT&T or Verizon to manage and operate
the VPN.
INTERNET Almost last, but certainly not least, of the
network types we will consider is the ubiquitous Internet.
The Internet could be considered a gigantic WAN, but it is
really much more than that. The Internetis a network of
networks that use the TCP/IP protocol (to be discussed
later in the chapter), with gateways (connections) to even
more networks that do not use the TCP/IP protocol. By
January 2010, there were approximately 733 million hosts
(number of IP addresses that have been assigned a name)
on the Internet (Internet Systems Consortium, 2010).
Internet World Stats estimated the number of Internet users
in September 2009 as 1,734 million, with nearly 253 million
users in North America (Internet World Stats, 2010). An
incredible array of resources—both data and services—is
available on the Internet, and these resources are drawing
more users, which are drawing more resources, in a
seemingly never-ending cycle.
The Internet has an interesting history, dating back to
1969 when the U.S. Department of Defense created
ARPANET^4 to link a number of leading research universi-
ties. Ethernet LANs incorporating TCP/IP networking
arrived in the early 1980s, and NSFNET was created in
1986 to link five supercomputer centers in the United
States. NSFNET served as the backbone (the underlying
foundation of the network, to which other elements are
attached) of the emerging Internet as scores of other
networks connected to it. Originally, commercial traffic
was not permitted on the Internet, but this barrier was
broken in the late 1980s, and the floodgates opened in the
early 1990s. In 1995, the National Science Foundation
withdrew all financial support for the Internet, and it began
funding an alternate very high-performance network
named vBNS—which was, in some respects, a forerunner
of Internet2 (to be discussed next).
The Internet has no direct connection to the U.S.
government or any other government. Authority rests with
the Internet Society, a voluntary membership organiza-
tion. The society is the organizational home for the groups
responsible for Internet infrastructure standards, including
the Internet Engineering Task Force and the Internet
Architecture Board. Similarly, the Internet receives no
government support now that NSF funding has ended.
Users pay for their own piece of the Internet. For an
individual, this usually means paying an ISP a monthly
fee to be able to dial a local number and log into the
Internet, or to access the Internet via a broadband service
such as DSL or cable. The smaller ISPs, in turn, pay a
fee to hook into the Internet backbone, which is a network
of high bandwidth networks owned by major ISPs such as
AT&T, Verizon, Sprint Nextel, Level 3 Communications,
and Qwest.
The Internet provides the four basic functions
summarized in Table 3.4: electronic mail, remote login,
discussion groups, and the sharing of data resources.
Electronic mailwas really the first “killer app” of the
Internet—the first application that grabbed the attention of
potential users and turned them into Internet converts.
Electronic mail provides an easy-to-use, inexpensive,
asynchronous means of communication with other Internet
users anywhere in the world. A newer variant of electronic
mail,instant messaging(IM), is a synchronous communi-
cation system that enables the user to establish a private
“chat room” with another individual to carry out text-based
communication in real time over the Internet. Typically,
the IM system signals the user when someone on his or her
private list is online, and then the user can initiate a chat
session with that individual. Major players in the IM
market are AOL, Yahoo!, Microsoft, and IBM Lotus.
Remote loginpermits a user in, say, Phoenix, to log
into another machine on which she has an account in, say,
Vienna, using a software program such as Telnet or the
more secure SSH. Then she can work on the Vienna
machine exactly as if she were there. Discussion groups
are just that—Internet users who have gathered together to(^4) ARPANET is a creation of the Advanced Research Projects Agency of
the U.S. Department of Defense. Much of the pioneering work on
networking is the result of ARPANET, and TCP/IP was originally
developed as part of the ARPANET project.