Using MIS 2e Chapter 6 Data Communications

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© Pearson Prentice Hall 2009

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Using MIS 2e


Chapter 6




Data Communications

David Kroenke


© Pearson Prentice Hall 2009

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Study Questions


Q1


What is a computer network?



Q2


What are the components of a LAN?



Q3


What are the alternatives for a WAN?



Q4


What criteria can you use for comparing WANs?



Q5


How does encryption work?



Q6


What is the purpose of a firewall?

© Pearson Prentice Hall 2009

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3


Q1


What is a computer network?



Q2


What are the components of a LAN?



Q3


What are the alternatives for a WAN?



Q4


What criteria can you use for comparing WANs?



Q5


How does encryption work?



Q6


What is the purpose of a firewall?

© Pearson Prentice Hall 2009

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Q1


What is a computer network?


The chart below describes three major types of networks
which are collections of computers that communicate
with each other over a variety of transmission lines. (The
Internet is discussed in Appendix 6A)

Fig 6
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1 Major Network Types

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Q1


What is a computer network?


Here are some additional characteristics of networks:



LAN communication lines reside on
-
premises, 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 the vendor to use the 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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Q1


What is a computer network?



Q2


What are the components of a LAN?



Q3


What are the alternatives for a WAN?



Q4


What criteria can you use for comparing WANs?



Q5


How does encryption work?



Q6


What is the purpose of a firewall?

© Pearson Prentice Hall 2009

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Q2


What are the components of a LAN?


This figure depicts a typical LAN. The components are usually
located within a half mile of each other.


A switch, located in the center, 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 new computers now


include an onboard NIC


that’s built into the


computer’s circuitry.


Fig 6
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2 Local Area Network (LAN)

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Q2


What are the components of a LAN?


A media access control (MAC) address serves as a unique identifier
for each NIC on a LAN.


Unshielded twisted pair (UTP) cables, shown on the left, are one
way to connect devices to a LAN.


Optical fiber cables, shown on the right, are also used to connect
devices to a LAN. The glass wires transmit signals in the form of
light rays. Cladding surrounds the core and contain the signals.
Optical fiber carries more traffic than UTP cables.


Fig 6
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3 Unshielded Twisted Pair (UTP) Cable

Fig 6
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5 Optical Fiber Cable

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Q2


What are the components of a LAN?

Fig 6
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4 Typical Arrangement of Switches in a Multistory Building


This figure shows how
a typical LAN might be
arranged in a
multistory building.
Notice the combination
of switches, UTP
cable, and optical fiber
cable on each floor.


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Q2


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.



The 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 support the 10/100/1000 Ethernet
protocol which describes transmission rate speed.



Communication speeds are expressed in bits like 1,000,000 for
megabits.

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Q2


What are the components of a LAN?


The IEEE 802.11 wireless protocol uses wireless NICs (WNIC) to
connect devices to networks similar to how wired NICs operate. The
most popular is IEEE 802.11g.


This figure depicts a


combination of NICs


and WNICs on a LAN.


It also shows access


points (AP) that use


the 802.3 protocol to


communicate with a


switch and the


802.11 protocol to


send and receive


wireless traffic.

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Q2


What are the components of a LAN?

Fig 6
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7 Summary of LAN and WAN Networks, Part 1


The chart on this slide and the next one is a summary of LAN and
WAN networks.

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Q2


What are the components of a LAN?

Fig 6
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7 Summary of LAN and WAN Networks Part 2

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Q1


What is a computer network?



Q2


What are the components of a LAN?



Q3


What are the alternatives for a WAN?



Q4


What criteria can you use for comparing WANs?



Q5


How does encryption work?



Q6


What is the purpose of a firewall?

© Pearson Prentice Hall 2009

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Q3


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).



The three primary functions of an ISP are:


To provide users with a legitimate Internet address


To serve as a gateway for users to connect to the Internet


To help pay for the Internet by collecting money from customers
and using it to pay access fees and other charges.

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Q3


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. The figure below compares the two kinds of
signals.



Fig 6
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8 Analog Versus Digital Signals

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Q3


What are the alternatives for a WAN?

Fig 6
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9 Personal Computer Internet Access


Modems are used to convert the signals back and forth as shown in
the figure below.


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Q3


What are the alternatives for a WAN?


A dial
-
up modem uses regular telephone lines and a
Point
-
to
-
Point Protocol (PPP) to connect a personal
computer to an ISP.



A 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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Q3


What are the alternatives for a WAN?


A 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.



A dial
-
up modem is considered narrowband because it
uses transmission speeds less than 56 kbps.



DSL and cable modems are considered broadband
because their transmission speeds exceed 256 kbps.

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Q3


What are the alternatives for a WAN?


Companies can use networks of leased lines from
telecommunications companies to connect computers located at
geographically distributed sites as this figure shows.


The lines use a variety of access devices to connect to each site:


Switches


Routers


special
-
purpose


computers that move


network traffic from


one node to another.


Only predefined sites can


use the leased lines.


These lines provide low
-
cost


connections if the amount of


traffic warrants it.

© Pearson Prentice Hall 2009

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Q3


What are the alternatives for a WAN?

Fig 6
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11 Transmission Line Types, Uses, & Speeds


This chart allows you to compare line types, uses, and speeds.

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Q3


What are the alternatives for a WAN?


This figure depicts a public switched data network, PDSN, that is
developed and maintained by a vendor who leases network time to
other organizations.


Each user site must lease a line on a PDSN. The line connection
location is called a Point of Presence (POP).


PDSNs are less costly and don’t require as much management
involvement as leased lines.


PDSNs use three protocols:


Frame relay with speeds


from 56 kbps to 40 Mbps


Asynchronous transfer


mode (ATM) with speeds


from 1 to 156 Mbps.


Ethernet with speeds from


10 to 40 Gpbs

© Pearson Prentice Hall 2009

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Q3


What are the alternatives for a WAN?


Virtual Private Networks (VPNs) create the appearance of private
point
-
to
-
point connections by using tunnels to create virtual, private
pathways over the Internet.


The figure below shows the actual connections a VPN uses.

Fig 6
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13 Remote Access Using VPN: Actual Connections

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Q3


What are the alternatives for a WAN?

Fig 6
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14 Remote Access Using VPN: Apparent Connection


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 and then decodes them when the user receives a
message.

© Pearson Prentice Hall 2009

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Q3


What are the alternatives for a WAN?

Fig 6
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15 WAN Using VPN


This figure shows how a WAN uses three different VPN
tunnels to connect geographically separated users.

© Pearson Prentice Hall 2009

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Q1


What is a computer network?



Q2


What are the components of a LAN?



Q3


What are the alternatives for a WAN?



Q4


What criteria can you use for comparing
WANs?



Q5


How does encryption work?



Q6


What is the purpose of a firewall?

© Pearson Prentice Hall 2009

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Q4


What criteria can you use for comparing WANs?


The following figures provide criteria you can use to
compare network alternatives based on three categories:
cost, performance, and other criteria.

Fig 6
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16 Criteria for Comparing Network Alternatives

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Q4


What criteria can you use for comparing WANs?

Fig 6
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16 Criteria for Comparing Network Alternatives

© Pearson Prentice Hall 2009

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Q4


What criteria can you use for comparing WANs?

Fig 6
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16 Criteria for Comparing Network Alternatives

© Pearson Prentice Hall 2009

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Q1


What is a computer network?



Q2


What are the components of a LAN?



Q3


What are the alternatives for a WAN?



Q4


What criteria can you use for comparing WANs?



Q5


How does encryption work?



Q6


What is the purpose of a firewall?

© Pearson Prentice Hall 2009

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Q5


How does encryption work?


The process of transforming clear text into coded, unintelligible text
for security reasons is called encryption.



It’s used to help make transmissions more secure across networks
and between users and Web sites.



Encryption algorithms use a key (number) to encode data in
messages before they’re sent and decode them when they reach
their destination.


Symmetric encryption uses the same key to encode and decode a
message.


Asymmetric encryption uses a different key to encode than is used to
decode a message.

© Pearson Prentice Hall 2009

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Q5


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 the 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.

© Pearson Prentice Hall 2009

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Q1


What is a computer network?



Q2


What are the components of a LAN?



Q3


What are the alternatives for a WAN?



Q4


What criteria can you use for comparing WANs?



Q5


How does encryption work?



Q6


What is the purpose of a firewall?

© Pearson Prentice Hall 2009

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Q6


What is the purpose of a firewall?


A computing device that prevents unauthorized network access is
called a firewall.


It can be a special
-
purpose computer or a program on a general
-
purpose
computer or router.


This figure shows a perimeter firewall that sits outside the network and is
the first device incoming network traffic encounters.


An internal firewall is located

inside the network and protects the LAN.

Fig 6
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17 Use of Multiple Firewalls

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Q6


What is the purpose of a firewall?


Packet
-
filtering firewalls, the simplest kind, examine the source
address, destination address, and other data in each incoming
message and decide 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 and
the firewall stops messages that are prohibited from entering the
network.



Every computer should have a firewall!