Using MIS 2e

Using MIS 2e


Chapter 6: Data Communications

Appendix: How the Internet Works


David Kroenke

This presentation has been
modified from the original and
should be downloaded from the
Course Documents area in
Blackboard


Study Questions (Chapter 6)


Q1
–

What is a computer network?


Q2
–

What are the components of a LAN?


Q3
–

What are the alternatives for a WAN?


Q4
–

How does encryption work?


Q5
–

What is the purpose of a firewall?


Reflection Guide: Human Networks Matter More

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Chapter 6/Appendix 6: Data Communications/Internet


A
computer network

is a collection of computers that
communicate with one another over transmission lines.


Three basic types of networks are:


Local area networks

(LANs)
–
connects computers that reside in a
single geographic location on the premises of the company that
operates the LAN.


Wide area networks

(WANs)
–
connects computers at different
geographic sites. WAN communication lines are owned by a third
-
party vendor.


Internet
–

a network of networks (the author defines an internet as
a network of networks and distinguishes between internets and the
Internet)


The networks that comprise the Internet use a large
variety of communication methods and conventions, and
data must flow seamlessly across them. This is
accomplished via
communications protocols
.

Q1
–

What is a computer network?

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Chapter 6/Appendix 6: Data Communications/Internet


A local area network (LAN) is a group of computers
connected together on a single company site.


A
switch

is a special purpose computer that receives and
transmits messages on a LAN.


Each device on a LAN has a hardware component called a
network interface card

(NIC)

or
wireless network interface
card (WNIC)
connects the device’s circuitry to the cable.


Each NIC (or WNIC) has a unique identifier, which is called the
(MAC)
media access control address
.


Communicating devices have two addresses: physical address
(MAC) and an IP address (logical address).


Devices on a LAN are connected using either Unshielded,
Twisted Pair (UTP) cable or optical fiber cables

Q2
–

What are the components of a LAN?

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Chapter 6/Appendix 6: Data Communications/Internet

Different protocols; e.g., 802.3 (also called
Ethernet
) or 802.11 (wireless) enable
communication among devices on a LAN. The WNICs connect via an access point

Q2
–

What are the components of a LAN?

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Chapter 6/Appendix 6: Data Communications/Internet

Q2
–

What are the components of a LAN?


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.


Communications speeds
are expressed in
bits
,
whereas memory sizes are
expressed in bytes; also
unlike memory,
K

and
M

imply
1,000

and
1,000,000

respectively as opposed to
2
10

and 2
20
.
Narrowband

refers to speeds less than
56 kbps;
Broadband

implies speeds in excess
of 256 kbps



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Chapter 6/Appendix 6: Data Communications/Internet

Q2
–

What are the components of a LAN?

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Chapter 6/Appendix 6: Data Communications/Internet


WANs connect computers located at physically separated
sites by obtaining connection capabilities from a third
-
party, typically an
Internet Service Provider (ISP).
The
network may be created using:


Leased lines

from telecommunication companies; the number of
lines increases dramatically as new sites are added; beneficial
when high volume of traffic occurs between fixed locations


Public switched network (PSDN)
, a network of computers and
leased lines that is developed and maintained by a vendor that
leases time on the network to other organizations; the organization
pays for the time it uses


Virtual private network (VPN)

use the Internet to create the
appearance of private point
-
to
-
point connections. VPN software
encrypts the messages to ensure security; offers the benefit of
point
-
to
-
point leased lines while enabling remote access

Q3
–

What are the alternatives for a WAN?

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Chapter 6/Appendix 6: Data Communications/Internet

Q3
–

What are the alternatives for a WAN (Connecting a PC)?


Connecting personal computers to an ISP requires that
digital

signals

coming out of the computer are converted to
analog

signals

and vice versa.
Modems

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


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Chapter 6/Appendix 6: Data Communications/Internet

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


You dial the number for your ISP and connect


The maximum speed is 56 kbps


A
DSL (digital subscriber line) modem

operates on the same lines as
voice telephones


The signals do not interfere with voice telephone service.


They provide much faster transmission speeds than dial up


They always maintain a connection.


May be symmetric or asymmetric (same or different upload and download
speeds)


A
cable modem

provides high
-
speed data transmission using cable
television lines.


Transmission speeds vary based on the number of network users


A
wireless modem
connects to a wireless network instead of to the
telephone system. When you connect with a wireless modem, you are
attached directly to your wireless ISP (Internet Service Provider)


Q3
–

What are the alternatives for a WAN (Types of Modems)?

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Chapter 6/Appendix 6: Data Communications/Internet

Q3
–

What are the alternatives for a WAN (Leased Lines)?

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


Only predefined sites can


use the leased lines.


These lines provide low
-
cost connections if the
amount of traffic warrants it.

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Chapter 6/Appendix 6: Data Communications/Internet

Q3
–

What are the alternatives for a WAN (PSDN)?


A public switched data
network (PSDN) is
developed and
maintained by a vendor
who leases network time
to other organizations.

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


PSDNs are less costly
and require less
management than
leased lines.

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Chapter 6/Appendix 6: Data Communications/Internet

Q3
–

What are the alternatives for a WAN (VPNs)?


Virtual Private Networks (VPNs) create the appearance of private
point
-
to
-
point connections by using tunnels to create virtual, private
pathways over the Internet; i.e., a VPN appears to be a direct
connection between two sites as shown in this figure.

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Chapter 6/Appendix 6: Data Communications/Internet


Software encrypts data as they pass through the VPN, then decodes
them when the user receives a message.


Encryption

is the process of transforming clear text into coded,
unintelligible text for secure storage or communication.


Consider a simple encryption scheme where each letter is
transposed by a constant (known as the key)


“Go Canes” becomes “Hp Dboft” (using key of 1)


“Go Canes” becomes “Iq Ecpgu” (using key of 2)


In this example:


Only 25 keys are possible which is too limited


This a
symmetric key

because the same key is used to encrypt and
decrypt a message. Both sender and recipient must keep the key secret.


In practice:


Web browsers use 2
128

possible keys (39
-
digit number)


Two different keys are used to encrypt and decrypt a message (an
asymmetric key
). The
public key

is freely distributed; the
private key

is
kept secret

Q4
–

How does encryption work?

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Chapter 6/Appendix 6: Data Communications/Internet

Most secure communication over
the Internet uses a protocol called
HTTPS.
With HTTPS, data are
encrypted using a protocol called
the Secure Socket
Layer/Transport Layer Security
(SSL/TLS).



Q4
–

How does encryption work?

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Chapter 6/Appendix 6: Data Communications/Internet


A
firewall

is a computing device that prevents unauthorized
network access. It can be a special
-
purpose computer or a
program on a general
-
purpose computer or on a router


Organizations normally use multiple firewalls (next slide).

Q5
–

What is the purpose of a firewall?

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Chapter 6/Appendix 6: Data Communications/Internet


A
perimeter firewall

sits outside the organization network; it
is the first device that Internet traffic encounters.


A
packet
-
filtering firewall

examines each packet and determines
whether to let the packet pass.


Packet
-
filtering firewalls can prohibit outsiders from starting a
session with any user behind the firewall.


They can also disallow traffic from particular sites, such as known
hacker addresses.


They can also prohibit traffic from legitimate, but unwanted
addresses, such as competitors’ computers.


Firewalls can filter outbound traffic as well.


Many organizations employ

internal firewalls
inside the
organizational network in addition to the perimeter firewall.
The internal firewall protects the LAN


Q5
–

What is the purpose of a firewall (multiple firewalls)?

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Chapter 6/Appendix 6: Data Communications/Internet

Reflection Guide
–
Human Networks Matter More











The Hungarian writer, Frigyes Karinthy, came up with the
idea that everyone on earth is connected to everyone else
by five or six people.

Suppose you want to meet your university’s president.


The president has a secretary who acts as a gatekeeper.


If you walk up to that secretary and say, “I’d like a half hour with
President Jones,” you’re likely to be palmed off to some other
university administrator. What else can you do?

Most successful professionals consistently build personal
human networks.


They meet people at professional and social situations, collect and
pass out cards, and engage in pleasant conversation (all part of a
social protocol) to expand their networks.


Who do you interact with at a company function, people or your
department or people in another department?


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Chapter 6/Appendix 6: Data Communications/Internet

Study Questions (Appendix Chapter 6)


Q1
–

How does email travel?


Ethics Guide: Sending Personal e
-
mail at work?


Q2
–

What is a communications protocol?


Q3
–

What are the functions of the five TCP/IP
—
OSI layers?


Q4
–

How does the Internet work?


Q4a
–

How is the Web different from the Internet?


Q4b
–

How do you create a Web site?


Q5
–

How does www.prenhall.com become 165.193.123.253?


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Chapter 6/Appendix 6: Data Communications/Internet

Should your friend give you his/her e
-
mail address at work?

You are on vacation in Hawaii and you
want to send a photograph to your
friend at work in the snow
-
bound
Midwest. You click send and the picture
arrives a minute later. You take it for
granted, but “a techno
-
miracle” has
occurred

You have a Dell, your friend has a Mac,
and you use different e
-
mail programs.
The LAN in your hotel uses wires, but
the LAN in your friend’s company is
wireless. Your message has to travel via
the Internet by underwater cable or
satellite, but it gets there. Amazing!

Q1
–

How does email travel?

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Chapter 6/Appendix 6: Data Communications/Internet


Sending/receiving personal e
-
mail from work generally
takes only a few minutes and consumes little of the
company’s resources. Is it OK to send personal e
-
mail?


What if you send a picture (or other large file) to your
friend? If you send 10 pictures to 100 friends? Where do
you draw the line?


What is the greater cost to the company; its resources or
your time? Is there a problem?


Is the activity illegal
?


Is the activity against company policy
?


Is the activity unethical
?


Is the activity smart?



Ethics Guide: Sending/Receiving personal e
-
mail at Work

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Chapter 6/Appendix 6: Data Communications/Internet


A protocol is a standard means for coordinating an activity
between two or more entities.


A
communications protocol

is a means for coordinating activity
between two or more communicating computers.


Two machines must agree on the protocol to use, and they must
follow that protocol as they send messages back and forth.


An
architecture

is an arrangement of protocol layers in
which each layer accomplishes a specific task


The most commonly used architecture is comprised of five levels
and is known as

TCP/IP
-
OSI architecture
.


A
program

is product that implements a protocol


Internet Explorer and Netscape are programs that implement the
HTTP protocol at the top level of the TCP/IP
-
OSI architecture

Q2
–

What is a communications protocol?

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Chapter 6/Appendix 6: Data Communications/Internet

Q3
–

What are the functions of the five TCP/IP
—
OSI layers?

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Chapter 6/Appendix 6: Data Communications/Internet


The Post Office is a good analogy of how the Internet works
(Ed Krol in
the Whole Internet, O’Reilly and Associates, 1992)


You drop a letter into a mailbox where it is picked up with
other letters and delivered to local post office


The letters are sorted and sent to another post office that is
closer to the destination


The process is repeated until the letter is eventually picked
up by the mail carrier at the other end and delivered to the
local destination


Each postal substation considers all of the routes available
and makes the best possible decision according to the
prevailing conditions


All that matters is the beginning and ending address; i.e., the
path may change the next time a letter is mailed


Q4
–

How does the Internet work (Overview)?

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Chapter 6/Appendix 6: Data Communications/Internet

All that matters is the beginning and ending address

Q4
–

How does the Internet work?

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Chapter 6/Appendix 6: Data Communications/Internet


Continue the Post Office analogy, but this time we are mailing
a book, not a letter. The Post Office (for whatever reason)
does not accept large packages and thus we have to rip the
pages out of the book and send them separately


Each page is placed in its own envelope and each envelope
(packet) is sent separately into the postal system


Each packet may travel a different route, but all packets are
assembled on the other end and then delivered


This may seem complicated, but it is actually quite clever:


Individual packets take turns using the connection medium
so that large packages (books) do not monopolize traffic


Each packet is checked for accuracy individually; if an error
is found only the individual packet has to be resent


All that matters is the starting and ending address; the path of
individual packets may change the next time a letter is mailed

Q4
–

How does the Internet work (TCP/IP)?

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Chapter 6/Appendix 6: Data Communications/Internet

D

D

E

F

D

E

E

D

E

F

D

TCP (Transmission Control
Protocol)
on Computer A
breaks message into packets

IP (Internet Protocol)

adds
the source and destination
address to each packet

1

TCP
on Computer D checks
the accuracy of individual
packets as they are received,
checks for missing packets,
then reassembles the message

3

The
router

reads the IP
addresses of individual
packets and routes
them to the destination;
e.g. Network 2 and
Computer D

2

Q4
–

How does the Internet work (Packet Switching)?

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Chapter 6/Appendix 6: Data Communications/Internet


HTTP

(Hyper Text Transfer Protocol) the protocol that is
used to transmit Web documents


HTTPS

–

Secure protocol for confidential transactions;
data is encrypted prior to being sent over the Internet


HTML

–

The main language in which Web documents
are displayed; uses codes to specify how the content
should appear to the user


URL

(Uniform Resource Locator)
–

the address of a
document on the Web


Web Browser

–

A software program used to locate and
display Web pages; e.g., Netscape or Internet Explorer


IP address

–

a series of dotted decimals that identifies a
unique device on a network

Q4
–

How does the Internet work? (Acronyms)?

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Chapter 6/Appendix 6: Data Communications/Internet


The Internet is a network of networks


Connects millions of computers in a global network where any
computer can communicate with any other computer, as long as
both have an Internet connection and follow Internet protocols


Supports multiple protocols and applications including e
-
mail,
news groups, instant messaging, HTTP, and FTP


Originally a project of the US government and ARPANet (1969)


The Web is a subset of the Internet which consists of
sites that process the HTTP protocol


Uses HTTP and Web browsers to access Web pages linked
together by hyperlinks


Created by
Tim Berners Lee

of CERN (1991)


The Internet is about computers whereas the Web is
about documents. The Web makes the Internet more
interesting, but the Internet makes the Web possible

Q4
–

How does the Internet work? (Internet versus the Web)

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Chapter 6/Appendix 6: Data Communications/Internet

Register.com

enables
you to search for the
domain name
(bobsgolfclubs.com)
and offers alternatives

Whois.com

shows the
owner of the domain
name and is useful if the
site does not yet exist;
i.e., you can buy it

Q4a
–

How do you create a Web site (Obtain a Domain Name)?

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Chapter 6/Appendix 6: Data Communications/Internet


Once you register a domain name, you will be contacted
by multiple developers seeking to create and/or host
your Web site.


Easiest initially to have the same company do both


The cost can vary from a few hundred dollars to many
thousands, depending on the nature of the site.


Four distinct steps
–

create, host, maintain, and attract


Create the site


Determine the complexity of the site; the more complex, the
more expensive. Complexity can go from merely displaying
information, to downloading documents, to simple security (log
-
in), to e
-
commerce


Navigation (depth of links; horizontal versus vertical links)


Determine a visual design; a simple template is inexpensive
whereas custom design adds significant


Q4a
–

How do you create a Web site?

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Chapter 6/Appendix 6: Data Communications/Internet


Host the site


After the site is created you need a company to host the site (i.e.,
provide a Web server) for you. The site should be
scalable
;
i.e.,
it should be built in such as way that you can simply add more
servers as traffic increases


Maintain the site


You want control of the content (at least initially); i.e., you should
be the one to add/modify content (e.g., the special of the month)


Attract visitors to the site


This is an entirely different issue and requires a marketing
campaign in conjunction with various search engines to direct
users to your site




Q4a
–

How do you create a Web site (continued)?

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Chapter 6/Appendix 6: Data Communications/Internet

Q5
–

How does www.prenhall.com become 165.193.123.253?


The
domain name system (DNS)

converts user
-
friendly names into
their IP addresses. Any registered valid name is a
domain name
.



Every domain name must be unique.


A non
-
profit agency (
ICANN
, Internet Corporation for Assigned Names
and Numbers) administers the registration of domain names.


The top
-
level domain (TLD) refers to the last letters in a domain name;
e.g., com, edu, and gov


Converting a domain name into an IP address is called Domain
Name Resolution


www.prenhall.com = 165.193.123.253


Domain name resolvers are computers that store the correspondence of
domain names and IP addresses.


Root servers maintain lists of IP addresses of servers that resolve each
type of TLD.


Each Web address is called a Uniform resource locator (URL); e.g.,
http://www.prenhall.com

is the URL for Prentice Hall.


The URL may contain additional information about the document or
folder where it is located; e.g.,
http://www.prenhall.com/kroenke


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Chapter 6/Appendix 6: Data Communications/Internet

Q5
–

How does www.prenhall.com become 165.193.123.253? (Top Level Domains 2005)

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Chapter 6/Appendix 6: Data Communications/Internet

www.warriorsofthe.net

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Chapter 6/Appendix 6: Data Communications/Internet

Summary


A
computer network

is a collection of computers that
communicate with one another over transmission lines.


Three types of computer networks are:
LANs
,
WANs
, and
the Internet.


A
protocol

is a set of rules for accomplishing the functions
of a particular layer.


An
architecture

is an arrangement of protocol layers; The
most commonly used architecture is comprised of five
levels and is known as
TCP/IP
-
OSI architecture


The Internet functions conceptually the same way as the
post office; i.e., all that matters is the ending address in
sending a message across the network.

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Chapter 6/Appendix 6: Data Communications/Internet

Summary (Continued)


The
Web

is a subset of the Internet which consists of sites
that process the
HTTP

protocol


The
domain name system (DNS)

converts user
-
friendly
names into their IP addresses. You can apply for your own
domain name using Register.com or a host of similar sites


Four distinct tasks associated with establishing a Web site
(Create, Host, Maintain, and Attract Customers)


Encryption

is the process of transforming clear text into
coded, unintelligible text for secure storage or
communication. An asymmetric approach is used with two
keys, one public and one private

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Chapter 6/Appendix 6: Data Communications/Internet

Review: Select the appropriate term for each item

1.
Subset of the Internet
World Wide Web

2.
Software application used to display Web pages

Browser

3.
Arrangement of protocol layers

Architecture

4.
He invented the Web

Berners
-
Lee

5.
The language of the Web

HTML

6.
Special purpose computer that implements the IP protocol
(the basic building block of the Internet)

Router

7.
Popular protocol for LAN

Ethernet

8.
Series of dotted decimals to identify a device

IP

Address

9.
An agreed upon format for transferring data between
computers

Protocol

10.
Protocol used to transmit Web documents

HTTP

11.
A secure Internet protocol

HTTPS

HTML
–

Architecture
–

HTTP
–

HTTPS
–

Protocol
–

Browser

–

World Wide Web
–

IP address
–

Router
–

Ethernet
–

Berners
-
Lee

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Chapter 6/Appendix 6: Data Communications/Internet