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Using MIS 3e
Chapter 6
Data Communication
David Kroenke
Chapter Preview
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If you go into business for yourself, there’s an excellent chance you’ll
have a problem just like Neil’s. How much do you really have to pay
toward a network infrastructure?
You’ll need the knowledge of this chapter to understand the
conversations you’ll have to make that assessment. Of course, you can
just rely on outside experts, but that probably doesn’t work in the 21st
century. Many of your competitors will be able to ask and understand
those questions—and use the money their knowledge saves them for
other facilities they need, like locker rooms and parking lots.
Or, what if youwork in productmanagementfor a large company? Does
your product “talk” to some network? If not, could it? Should it? Does it
require a LAN or a WAN? As stated mega-times already, data
communication is nearly free today, generating exciting opportunities.
This trend makes basic knowledge of this free resource even more
important.
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Chapter Preview (cont’d)
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To help you be prepared, we will discuss the overarching concepts of
computer networks and related technology. We will greatly simplify the
discussion, but, even still, this topic involves the interaction of dozens of
equipment types, methods, and standards and a sea of terms and
acronyms. To help you deal with this complexity, we divide this topic into
a conceptually oriented chapter and a supplemental appendix with more
details.
In particular, this chapter defines three types of computer networks and
discusses the components and alternatives for two of those types: local
area networks (LANs) and wide area networks (WANs). It then explains,
at a high level, how computer encryption works and finally describes
firewalls, which are devices for protecting networks from unauthorized
access and use.
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Study Questions
Q1 What is a computer network?
Q2
Q3
Q4
Q5
Q6
Q7
What are the components of a LAN?
What are the alternatives for a WAN?
Why do organizations use virtual private networks?
How does encryption work?
What is the purpose of a firewall?
2020?
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6-4
What Is a Computer Network?
• Computer network is a collection of computers that communicate
with one another over a variety of transmission lines.
• Three basic types of networks: LAN, WAN, Internet (The Internet
is discussed in Appendix 6A)
• (video)
Figure 6-1 Major Network Types
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What Is a Computer Network?
• Additional characteristics of networks:
 LAN communication lines reside onpremises, making it easier for a business to
locate a network wherever it chooses.
 WAN communication lines are owned by a
third-party vendor. A business contracts
with vendor to use its WAN lines.
 Each type of network uses protocols which
are sets of rules that two devices use to
communicate with each other.
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Study Questions
Q1
What is a computer network?
Q2
What are the components of a LAN?
Q3
Q4
Q5
Q6
Q7
What are the alternatives for a WAN?
Why do organizations use virtual private networks?
How does encryption work?
What is the purpose of a firewall?
2020?
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What Are the Components of a
LAN?
• Components are usually located within a half mile of each other.
• A switch is a special-purpose computer that receives and
transmits messages to computers in the LAN.
• A network interface card (NIC)
is a hardware component that
connects each device’s circuitry
to a cable allowing protocols to
send data across the LAN.
• Most computers today
include an NIC.
Fig 6-2 Local Area Network (LAN)
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What Are the Components of a
LAN?
• Media access control (MAC) address serves as a unique
identifier for each NIC on a LAN.
• Unshielded twisted pair (UTP) cables, shown on left, are one
way to connect devices to a LAN.
• Optical fiber cables, shown on right, connect devices to a LAN
using fiberglass wires to transmit signals which are light rays.
Cladding contain the signals. Optical fiber carries more traffic
than UTP cables.
Fig 6-3 Unshielded Twisted Pair (UTP) Cable
Fig 6-5 Optical Fiber Cable
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What Are the Components of a
LAN?
• Typical arrangement of
switches in a multistory
building
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What Are the Components of a
LAN?
• The IEEE, Institute for Electrical & Electronics Engineers, is a
committee that creates and publishes protocols and standards
used by virtually every network.
• IEEE 802.3, or Ethernet, protocol is used by all LAN devices. It
specifies hardware characteristics and describes how messages
are packaged and processed.
• Onboard NICs in new PCs support10/100/1000 Ethernet protocol
which describes transmission rate speed.
• Communication speeds are expressed in bits like 1,000,000 for
megabits.
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What Are the Components of a
LAN?
• IEEE 802.11 wireless
protocol uses wireless NICs
(WNIC) to connect devices to
networks similar to how wired
NICs operate.
• Figure depicts a combination
of NICs and WNICs on a
LAN.
• Access points (AP) use
802.3 protocol to
communicate with a switch
and 802.11 protocol to send
and receive wireless traffic.
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Summary of LAN and WAN
Networks
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Study Questions
Q1
Q2
What is a computer network?
What are the components of a LAN?
Q3
What are the alternatives for a WAN?
Q4
Q5
Q6
Q7
Why do organizations use virtual private networks?
How does encryption work?
What is the purpose of a firewall?
2020?
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What Are the Alternatives for a
WAN?
• WANs connect computers located at physically
separated sites by obtaining connection capabilities
from a third-party, typically an Internet Service
Provider (ISP).
• Three primary functions of an ISP are to:
1. Provide users with a legitimate Internet address
2. Serve as a gateway for users to connect to the
Internet
3. Help pay for the Internet by collecting money
from customers and using it to pay access fees
and other charges
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What Are the Alternatives for a
WAN?
• Connecting personal computers to an ISP requires that digital
signals coming out of the computer are converted to analog
signals. Analog signals coming into a personal computer must be
converted to digital signals.
Comparison of digital and analog signals.
Fig 6-8 Analog Versus Digital Signals
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What Are the Alternatives for a
WAN?
Fig 6-9 Personal Computer Internet Access
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What Are the Alternatives for a
WAN?
• Dial-up modem uses regular telephone lines and a Point-to-Point
Protocol (PPP) to connect a personal computer to an ISP.
 Dial-up modem is considered narrowband because it uses
transmission speeds less than 56 kbps.
• DSL modem shares a single communication line for a telephone
and a personal computer. It’s much faster than a dial-up modem
and allows a user to maintain a constant network connection with
an ISP.
 Asymmetric DSL, ADSL, provides different upload/download
speeds.
 Symmetrical DSL, SDSL, provides the same
upload/download speeds.
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What Are the Alternatives for a
WAN?
• Cable modem shares a single communication line for
cable TV and a personal computer. It’s also faster
than a dial-up modem and allows users to maintain a
constant network connection.
 Because cable modems use a neighborhood
distribution center, transmission speeds vary
based on the number of network users.
• DSL and cable modems are considered broadband
because their transmission speeds exceed 256 kbps.
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What Are the Alternatives for a
WAN?
• Leased lines from telecommunications companies to connect
computers located at geographically distributed sites (see figure)
• Lines use a variety of access devices to connect to each site:
Switches and Routers—
special-purpose computers
that move network traffic
from one node to another.
• Only predefined sites can
use the leased lines.
• These lines provide lowcost connections if amount
of traffic warrants it.
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What Are the Alternatives for a
WAN?
Comparison of line types, uses, and speeds.
Fig 6-11 Transmission Line Types, Uses, and Speeds
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What Are the Alternatives for a
WAN?
• Public switched data network, PDSN, developed and maintained
by a vendor who leases network time to other organizations.
• Each user site must lease a PDSN line connection called a Point
of Presence (POP).
• PDSNs are less costly, don’t
require as much management
involvement as leased lines.
• Uses three protocols:
1. Frame relay with speeds
from 56 kbps to 40 Mbps
2. Asynchronous transfer
mode (ATM) with speeds
from 1 to 156 Mbps.
3. Ethernet with speeds from
10 to 40 Gpbs
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Study Questions
Q1
Q2
Q3
What is a computer network?
What are the components of a LAN?
What are the alternatives for a WAN?
Q4 Why do organizations use virtual private
networks?
Q5
Q6
Q7
How does encryption work?
What is the purpose of a firewall?
2020?
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Why Do Organizations Use Virtual
Private Networks?
• Virtual Private Networks (VPNs) create the appearance of private
point-to-point connections by using tunnels to create virtual,
private pathways over the Internet.
• Figure below shows connections a VPN uses.
Fig 6-13 Remote Access Using VPN: Actual Connections
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Why Do Organizations Use Virtual
Private Networks?


A VPN appears to be a direct connection between two sites
as shown in this figure.
Software encrypts data as they pass through the VPN making
them more secure. Then, decodes when user receives them.
Fig 6-14 Remote Access Using VPN: Apparent Connection
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Why Do Organizations Use Virtual
Private Networks?

This figure shows how a WAN uses three different VPN tunnels
to connect geographically separated users.
Fig 6-15 WAN Using VPN
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Study Questions
Q1
Q2
Q3
Q4
What is a computer network?
What are the components of a LAN?
What are the alternatives for a WAN?
Why do organizations use virtual private networks?
Q5
How does encryption work?
Q6
Q7
What is the purpose of a firewall?
2020?
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How Does Encryption Work?
• Encryption—process of transforming clear text into coded,
unintelligible text for security reasons is called encryption.
• Used to make transmissions more secure across networks and
between users and Web sites.
• Encryption algorithms use a key (number) to encode data in
messages before sending and decode them when they reach
their destination.
 Symmetric encryption uses same key to encode and decode a
message.
 Asymmetric encryption uses a different key to encode than is used
to decode a message.
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How Does Encryption Work?
• Public key/private key is a special version of
asymmetric encryption mainly used on the Internet.
 The public key encodes a message and is exchanged among
users.
 The private key decodes a message but is never exchanged
among users.
• HTTPS is most secure protocol used on the Internet.
 Secure Socket Layer (SSL), also known as Transport Layer
Security (TLS), combines public key/private key with
symmetric encryption to establish a secure exchange of data
on a Web site.
 Web sites using this type of security will have https:// at the
beginning of the URL.
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Study Questions
Q1
Q2
Q3
Q4
Q5
What is a computer network?
What are the components of a LAN?
What are the alternatives for a WAN?
Why do organizations use virtual private networks?
How does encryption work?
Q6
What is the purpose of a firewall?
Q7
2020?
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What is the Purpose of a Firewall?
• Firewall—a special-purpose computer or a program on a
general-purpose computer or router that prevents unauthorized
network access.
• Figure shows a
perimeter firewall that
sits outside the network
and is first device
incoming network traffic
encounters.
• An internal firewall is
located inside the
network and protects the
LAN.
Fig 6-17 Use of Multiple Firewalls
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What is the Purpose of a Firewall?
•
Packet-filtering firewalls examine the source address, destination
address, and other data in each incoming message and decides
whether to let the message enter the network.
•
Packet-filtering firewalls prohibit outsiders from starting a session with
users behind the firewall, disallow traffic from particular sites, and filter
outbound traffic.
•
Each incoming message is compared to an access control list (ACL).
Firewall stops prohibited messages from entering the network.
•
Many ISPs provide generic firewalls for customers. Large organizations
supplement generic firewalls with their own.
•
Most home routers include firewalls, and Windows XP, Vista, and
Windows 7 have built-in firewalls as well. Third parties such as Norton
and Symantec also license firewall products.
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Study Questions
Q1
Q2
Q3
Q4
Q5
What is a computer network?
What are the components of a LAN?
What are the alternatives for a WAN?
Why do organizations use virtual private networks?
How does encryption work?
Q6
What is the purpose of a firewall?
Q7
2020?
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2020?
• ISPs will charge based on number of bits sent and received.
• Streamlined Sales Tax Project—more states will collect sales
taxes on Internet purchases regardless of whether seller has
physical presence in the state.
• Everything will be connected to everything, everywhere, and
everything will be inter-connected (Microsoft Office
Communicator).
• You’ll be receiving email via phone (a voice will read it to you),
and phone via email (a voice-recognition system will type it). All
messages, of whatever medium, will be stored in one location.
• Systems will provide presence, so you’ll know who is on the
system, who is available, and who cannot currently be reached.
• Communications will be ubiquitous.
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Ethics Guide: Personal Email at
Work?
• You emailed a very high-quality (nonpornographic) picture that
was 6.2 megabytes in size to a friend.
• What’s the matter with this email and a picture?
• Consider the resources consumed:
 Your message, and picture, traveled over the Internet to
OhioCompany’s ISP. Packets of the email and picture were
transmitted to OhioCompany’s router and then to its email server.
 It consumed processing cycles on the router and on the email server
computer. A copy of picture is stored on email server until your
friend deletes it.
 Picture saved on company-owned PC.
• Entire computing infrastructure, from ISP to your friend’s desk, is
owned, operated, and paid for by OhioCompany.
• Your friend reads his email during his working hours.
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Guide: Thinking Exponentially Is
Not Possible, but…
• Nathan Myhrvold claimed that humans:
 Cannot think exponentially
 Think of fastest linear change and extrapolate from there
• Was writing about growth of magnetic storage
• Applies to growth of computer network phenomena
• Ubiquitous and cheap connectivity is growing
exponentially
 What are the threats and opportunities?
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Guide: Thinking Exponentially Is
Not Possible, but…
• Technology doesn’t drive people to do new things
• Social progress occurs in small, evolutionary,
adaptive steps
• Technology may enable a capability, but people may
not want it
 People want to do what they are doing more easily.
 They want to solve existing problems.
• Respond by hedging your bets
• The more time involved, the more potential for error
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Ethics Guide: Human Networks
Matter More
• Six degrees of separation
 Social networks are crucial in connecting you to everyone in
six degrees.
 In general, people you know the least contribute the most to
your network.
• Build personal social networks for success
 Someone, somewhere, that you need to know or will need to
know
 Meet people at professional and social situations
• Pass out and collect business cards
• Converse to expand network
• Look for new channels
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Active Review
Q1
Q2
Q3
Q4
Q5
Q6
Q7
What is a computer network?
What are the components of a LAN?
What are the alternatives for a WAN?
Why do organizations use virtual private
networks?
How does encryption work?
What is the purpose of a firewall?
2020?
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6-39
Case Study 6: Keeping Up with
Wireless
• WiMax—a standards-based technology for wireless broadband
access, alternative to cable and DSL Internet access (How
WiMax works)
• Last-mile problem—getting broadband access into homes and
small businesses
• WiMax Forum CertifiedTM systems to have capacity of 40 Mbps
per channel, for fixed, nomadic, portable, and mobile applications
• IEEE 802.16-2004 and IEEE 802.16e wireless standards
• Clearwire and Craig McCaw
• Wireless Broadband Introduction (education)
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All rights reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted, in any form or by any means, electronic,
mechanical, photocopying, recording, or otherwise, without the prior written
permission of the publisher. Printed in the United States of America.
Copyright © 2011 Pearson Education, Inc.
Publishing as Prentice Hall
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