Transcript Chapter 7

Basic Computer Application
Chapter 7
The Web and E-mail
7 Chapter Contents
Section A: Web Technology
Section B: Search Engines
Section C: E-commerce
Section D: E-mail
Section E: Web and E-mail Security
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7 Web Basics
The Web is an interlinked collection of
document, image, video, and sound files
A Web site contains a collection of related
information
Podcasts
RSS vs. Atom
Videocasting
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7 Web Basics
A Web page is the product or output of one or more
Web-based files displayed in a format similar to a
page in a book
A Web browser is client software that displays Web
page elements and handles links between pages
Every Web page has a unique address called a
URL
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7 HTML
Set of specifications for creating documents
that a browser can display as a Web page
Markup language
HTML tags
XHTML – Extensible HTML
DHTML – Dynamic HTML
Ajax – Asynchronous JavaScript and XML
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7 HTML
UTA Example
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7 HTTP
HTTP messages flow
between a browser
and a Web server.
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7 Web Browsers
Help you access Web pages
Upgrade to new browser
versions as they become
available
Popular browsers:
–
–
–
–
–
Internet Explorer
Mozilla Firefox
Apple Safari
Netscape Navigator
Opera
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7 Cookies
Small chunk of data generated by a Web
server and stored on computer’s hard disk
– Fix problems caused by HTTP’s stateless
protocol
– Relatively safe
Your computer does not have to accept
cookies
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7 Web Page Authoring
Text editor
HTML conversion tool
Online Web authoring
tools
Web authoring software
– Microsoft FrontPage
– Adobe Dreamweaver
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7 HTML Scripts
HTML scripts can perform complicated tasks
and respond to user actions
– HTML forms
– Server-side script
– Client-side script
– Java applet
– ActiveX control
Digital Certificate
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7
SECTION
B
Search Engines
Search Engine Basics
Formulating Searches
Citing Web-based Source Material
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7 Search Engine Basics
 A Web crawler is a computer program that is automated to
methodically visit Web sites
 A search engine indexer is software that culls keywords from
a Web page and stores them in a database
 A search engine’s query processor looks for your search
terms in search engine’s indexed database and returns list of
relevant Web sites
 Link popularity is measured by quantity and quality of links
from one Web page to others
 A meta keyword is entered into a header section of a Web
page when it is created and is supposed to describe the
page contents
– Keyword stuffing
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7 Formulating Searches
Most search engines
work with keyword
queries in which you
enter one or more
words, called search
terms
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7
SECTION
C
E-commerce
E-commerce Basics
Online Shopping
Online Auctions
Online Payment
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7 E-commerce Basics
Business transactions conducted
electronically over a computer
network
– B2C (business-to-consumer)
– C2C (consumer-to-consumer)
– B2B (business-to-business)
– B2G (business-to-government)
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7 Online Shopping Transactions
In a typical shopping
session, you connect to
an online storefront and
use navigation controls
to browse through the
merchant’s catalog. As
you browse, you can
drop items into your
electronic shopping cart.
At the checkout counter,
you enter the information
necessary to pay for the
items you selected.
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7 Online Shopping
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7 Shopping Carts
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7 Online Payment
A secure connection encrypts the data
transmitted between your computer and a
Web site
• SSL (Secure Sockets Layer)
• S-HTTP (secure HTTP)
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7
SECTION
D
Web Technology (bonus)
The Internet Protocol Stack
Application Ports
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7 Internet Protocol Stack
Nodes attached to the Internet implement a
standard set of capabilities to allow
communications between dissimilar systems
across dissimilar communications links
The standard protocol “stack” is implemented
in a layered design to support modularity and
ease of implementation in many different
environments.
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7 Internet Protocol Stack
Think of each layer as
application
HTTP,
etc.
a different system
software program that
transport
TCP
or UDP
runs on your computer.
The upper layers allow
network
IP
like applications to
communicate
link
Ethernet
The lower layers allow
like devices to
UTP,physical
fiber, etc.
communicate
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APPLICATION
CATEGORY
DEPENDENT
OPERATING
SYSTEM
CONTROLLED
NETWORKE
HARDWARE
DEPENDENT
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7 Internet Protocol Stack
Your Client
Application
Web browser,
email client, etc.
Web server, email
server, etc.
Target Server
Application
transport
transport
network
network
link
physical
packets
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Your Messages
application
Your Messages
application
link
The
Internet
physical
packets
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7 Internet Ports
The means by which
a single physical
node differentiates
multiple requests,
like email, web, file
transfer, etc.
The transport layer
passes requests to
specific “ports” into
the application layer
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Email
Application
Web Server
Application
File Transfer
Application
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transport
network
link
physical
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7
SECTION
D
E-mail
E-mail Overview
Netiquette
E-mail Technology
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7 E-mail Technology
E-mail systems carry and manipulate e-mail
messages
– E-mail servers
– Based on store-and-forward technology (SMTP)
Three types of e-mail client systems widely
used today:
– POP
– IMAP
– Web-based e-mail
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7 E-mail Technology
A POP server is a
computer that stores
your incoming
messages until they
can be transferred to
your hard disk
– E-mail client software
An SMTP server is a
server that forwards
emails that you send
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7 E-mail Technology: SMTP mail
1) Alice uses an email client
program to compose a
message and “to”
[email protected]
2) Alice’s mail client sends the
message to her mail server
where it is placed in a
message queue (SMTP)
3) Client side of opens a
“connection” with Bob’s
mail server
1
user
agent
2
mail
server
3
4) The client-side mail server
sends Alice’s message over
the connection (SMTP)
5) Bob’s mail server places the
message in Bob’s mailbox on
the server
6) Bob opens his email client
program to download and
read Alice’s message (POP3)
mail
server
4
5
6
user
agent
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Chapter 7: The Web and E-mail
Slide from Computer Networks: A Tops-Down Approach, Kurose and Ross
7 E-mail Technology: Web mail
Web-based e-mail accounts allow you to use
a browser to access your e-mail messages
 Messages are sent as form data between
the client and the server using HTTP (not
SMTP/POP).
 Your Web server re-formats and then
forwards your email using SMTP.
1
Web
Client
2
HTTP
Chapter 7: The Web and E-mail
mail
server
Web Mail
HTTP SMTP
3
4
5
SMTP
6
7
user
agent
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7 Web and E-mail Security
SECTION
E
Cookie Exploits
Fake Sites
Spam
Phishing
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7 Cookie Exploits
An ad-serving cookie can track your activities
at any site containing banner ads from a third
party
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7 Fake Sites
 A fake Web site
looks legitimate, but
has been created by
a third party to be a
very clever replica of
a legitimate Web site
 Pharming is an
exploit that redirects
users to fake sites
by “poisoning” a
domain name server
with a false IP
address
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7 Spam
Spam is unwanted electronic junk mail about
medical products, low-cost loans, and fake
software upgrades that arrives in your online
mailbox
A spam filter is a type of utility software that
captures unsolicited e-mail messages before
they reach your inbox
– Local filtering
– ISP filtering
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7 Phishing
Phishing is an e-mail based scam designed
to persuade you to reveal confidential
information, such as your bank account
number or Social Security number
If you don’t want to become a phishing victim,
be suspicious of e-mail messages that
supposedly come from banks, ISPs, online
payment services, operating system
publishers, and online merchants
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Basic Computer Application
Chapter 7 Complete
The Web and E-mail