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Information Systems by Efrem G. Mallach

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185
Chapter 6
Information Networks
CHAPTER OUTLINE
Communication Links and Networks
Communication Links and Devices
Local Area Networks
Wide Area Networks and the Internet
Internet Applications
Network Security
WHY THIS CHAPTER MATTERS
ose who supply data to an information system, those who use its output, and its comput-
ers are seldom all in the same place. When an information system serves people in dierent
places, such as everyone who reserves a seat on a United Airlines ight, buys music at the
iTunes Store, or follows a Twitter hashtag, they cannot be. We need to move data from one
place to another.
at is where data communication networks come in. Along with shared databases, net-
works are one of the two key enabling technologies that make modern information systems
possible.
Some technical decisions about networks are best le to experts, but many require
understanding both business and how the technology works. Aer you study this chapter,
you should be well positioned for those decisions.
CHAPTER TAKE-AWAYS
As you read this chapter, focus on these key concepts to use on the job:
1. Having the right communications and networks is key to strategic applications.
2. Dierent communications and networking options involve dierent tradeos, and
are best suited to dierent organizations or applications.
186 Information Systems: What Every Business Student Needs to Know
3. Long-distance communication is almost entirely over the Internet today, so most
business choices involve local communication and connecting to the Internet.
4. Network security is a management responsibility, even when it is supported by
technology.
COMMUNICATION LINKS AND NETWORKS
Ebay, Amazon, and the iTunes store cannot, and do not, build direct communication links
from their servers to the computers of every customer such as yourself. ey, and every other
online user, share large public networks. In order to make business decisions involving those
networks, we need to know a bit about how they work. ey involve two basic concepts:
1. A communication link is a means of transmitting data from a device at one end of the
link to a device at its other end.
2. A network is a collection of communication links with the ability to route messages
among devices attached to the network.
Communication links are the building blocks of networks. In addition to the links, a net-
work uses devices to examine messages and route them correctly. e concepts are analo-
gous to those of roads and a road network. A road network consists of roads, junctions
where vehicles can turn from one road to another, and control devices such as stop signs
and trac signals.
COMMUNICATION LINKS AND DEVICES
Many technologies can be used to transmit data. e range of choices can be bewildering.
Communication links fall into two major categories: physical (wired) links and wireless links.
As you read about types of communication links, and as you learn of new types in the
future, keep in mind that everything sent over these links is managed by soware. A link
sends signals from point A to point B. Hardware at the ends of the links turns signals into
1s and 0s. What the 1s and 0s mean is up to the soware that sends and receives them. e
soware at the two ends must agree on their meaning. Fortunately, there are standards for
this. For example, a standard called HTML denes how to send Web pages. e computer
that sends a page sends it in HTML. Your browser (Chrome, Firefox, etc.) turns that HTML
into a page on your screen.
e soware to operate communication links, and to route messages to and from appli-
cations, is built into all modern operating systems. It performs two OS functions: manag-
ing shared resources (the communication link) and providing shared services (sending
and receiving data).
Physical Communication Links
Copper wires have been used to transmit signals since the telegraph. Since the telephone
network connected every location of interest in the industrialized world, it was also applied
for data.

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