گارگاه کامپيوتر
The Internet & the World
Wide Web
)(concepts
تييو كننده: علي برادران ىاشمي
ARPANet
Advanced Research Projects Agency Network
1969 – US Department of Defense and
Rand Corporation
Origins
Cold War – fear that a bomb could
demolish computing capabilities
Several computers, geographically
dispersed, networked together
Plan – if one computer was disabled,
others could carry on using alternative
communication routes
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ARPANet
Transmitting the Message
Messages divided into packets
TCP/IP protocol
TCP – does the packeting and
reassembling of the message
IP – handles the addressing
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ARPANet
Expands Beyond the Military
Research computers from universities
Defense contractors
Needed technical expertise to work on
Internet
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Tim Berners-Lee
1990
Perceived a spider’s web of computers
with links from computer to computer
CERN site
Dr. Berners-Lee’s physics laboratory
Birthplace of the World Wide Web
Easy movement due to links
Hypertext
Hyper-region
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Marc Andreessen
1993
Created browser software
Mosaic – first browser
Provided attractive images and a
graphical interface permitting users to
click on pictures as well as text
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ARPANet to Internet
TCP/IP software is public domain
Network became more valuable as it
embraced other networks
ARPANet disappears
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Internet Explosion
Mid 1990s
Estimate over 333 million users
worldwide
Part of our daily lives
Four factors
TCP/IP standard
Ability to link from site to site
Ease of use of browser
Growth of PC and LANs that can connect
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URL
Uniform Resource Locator
http://domain-name.top-level-domain/last-section
Unique address of a web page or file on the
Internet
Case-sensitive
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http
hypertext transfer protocol
http://domain-name.top-level-domain/last-section
Protocol – rules
Communication using links
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Domain name
http://domain-name.top-level-domain/last-section
Address of the ISP
Domain names are registered
Ongoing fee is paid for each domain
name
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Top-level Domain
Represent the purpose of the organization of
entity
.com
.gov
.edu
.org
.net
12 May be a two-letter country code (.ir)
Last section
http://domain-name.top-level-domain/last-section
Directories and file names that specify a
particular web page
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URL (Universal Resource Locator)
URLs--addresses for web pages
http://www.aut.ac.ir/departments/index.htm
Protocol : http://
Protocol - a set of communication rules for exchanging
information.
Domain name: aut.ac.ir
Directory name: departments
14 File name: index.htm
Getting Started
Computer with a modem or NIC
Internet service provider (ISP)
Browser
Related software
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Internet Service Provider
Vehicle to access the Internet
Provides
Server computer
Software to connect
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Choosing Your Internet Access
Device & Physical Connection
Bandwidth - an
expression of how
much data can be
sent through a
communications
channel in a given
amount of time
Broadband - very
high speed
connection
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Transmission speeds
Transmission speeds:
Bps - bits per second.
Kbps - kilobits per second, or 1000 bits per second.
Mbps - megabits per second, or 1 million bits per
second.
The prefix “mega” in “megabits” comes from the
Greek word “megas” meaning “mighty” or “great.”
Gbps - gigabits per second, or 1 billion bits per second.
The prefix “giga” in “gigabits” comes from a Greek
word meaning “giant.”
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Telephone (Dial-Up) Modem: Low Speed
but Inexpensive & Widely Available
Modem - device that
sends and receives
data over telephone
lines to and from
computers
Most modems today
have a maximum
speed of 56 Kbps.
dial-up connection.
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High-Speed Phone Lines: More
Expensive but Available in Most Cities
ISDN - hardware and software that allows
voice, video, and data to be communicated over
traditional copper-wire telephone lines
128 Kbps
DSL - also uses regular phone lines but much
faster than ISDN
1.5-8.4 Mbps download; 16-640 Kbps upload
T1 - a traditional trunk line that carries 24
normal telephone circuits and has a transmission
rate of 1.5 Mbps
T1 - 1.5 Mbps
Generally used by corporate, government, & academic
sites.
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Cable modem
Cable Modem: Close Competitor to
DSL
Always “on” (like DSL)
Download transmission speed of 10 Mbps
Upload transmission speed of 500 Kbps
Subject to slowdowns during peak-load times
Cable modem - connects a personal
computer to a cable-TV system that
offers an Internet connection
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Choosing Your Internet Service
Provider (ISP)
ISP - a company
that connects you
through your
communications line
to its servers, or
central computer,
which connect you to
the Internet via
another company’s
network access
points
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Wireless Internet Access
Supports mobile handheld devices
Text pagers
PDAs
Pocket computers
Web-enabled cellular phones
Applications
E-mail
Checking weather
Making airline reservations
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Wireless Internet Access
Need
Account with wireless access provider
Cellular modem card or adapter
Wireless Application Protocol (WAP)
Convert web pages into format for mobile
devices
Resized for limited display area
Fewer graphics transmitted
Slow download speeds
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The World Wide Web
Q: What makes
the Web
graphically
inviting?
A: Multimedia
Q: What makes
the Web easily
navigable?
A: Hypertext
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The World Wide Web (Cont.)
Multimedia (from “multiple media”) - technology that
presents information in more than one medium,
including text graphics, animation, video, and sound.
Hypertext - a system in which documents scattered
across many Internet sites are directly linked--with
hyperlinks--so that a word or phrase in one document
becomes a connection to a document in a different
place.
HTML (Hypertext Markup Language) - the set of
special instructions (called “tags”) that are used to
specify document structure, formatting, and links to
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other multimedia documents.
The Web & How It Works
Website--the domain on the computer
Site - a computer with a domain name
Example: www.aut.ac.ir
Website - the location of a web domain name in a
computer somewhere on the Internet
Web pages--the documents on a website
Web page - a document on the WWW that can include
text, pictures, sound, and video
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Browser
Netscape Communicator
Microsoft Internet Explorer (IE)
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Browser
Used to explore the Internet
Display web pages
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Browser
Functions and Features
Browser display window
Displays contents of web page from each
Internet site visited
Screen limits how much of the site you can
view at a time. The page can be scrolled
using the scroll bar to see its entire contents
Status line – progress of data being
transferred and other messages
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Browser
Functions and Features
Welcome banner on title bar
Browser logo – animation indicates you are in
the process of moving to a new site
Hot list
Bookmark
Favorites
Store your favorite URLs
Browser control panel – menus and buttons
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Browser
Menus and Buttons
Pull-down menu
Buttons
Convenient shortcuts for commonly used
functions
Click button rather than locate command
from pull-down menu
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Browser Support
Frames
Divides page into rectangular sections
Each section displays web pages
independently
Several small pages on one screen
Can be scrolled independently
Can be replaced with other pages independently
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Plug-ins
Software that increases the functionality
of a browser
Audio-video
Image viewing
Download from web sites
Install
Example
Adobe Acrobat Reader
Shockwave
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Programming
ActiveX Controls
Capabilities similar to Java
Browser must be enabled to support
applets / ActiveX Controls
Security issues
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Moving Between Sites
Clickable categories in the browser
Sports
Weather
News
Technology
Comic strips
Enter the URL in the address text box and
press
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Processing Requests
URL
User enters a URL
User computer sends request to the ISP
server
ISP server sends request across networks
of TCP/IP computers
Destination site is reached
Content is transmitted back to your
computer (process in reverse)
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Searching the Internet
Search engine
User specifies a search request
Browser links to Search Engine
Request returns matching pages based
upon the Search Engine’s database
Results presented
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Processing Requests
Search Engine Database
Search Engine builds database
Searchable terms
Related web sites
Spider, robot, bot
Follows links across the web
Automatically indexes pages to a database
One word
All words
Pages may be submitted by the owner
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Processing Requests
Search Engine Database (Cont.)
Request same search using different
engines yields different results
Databases built independently
Size
Content
Search methodology
Metasearch – atomically puts the same
request to several search engines
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Processing Requests
Directory vs. Search Engine
Directory
Human involvement!
Sites organized by content category
May concentrate on specific content areas
Subjective decisions regarding inclusion and
importance
Search Engine
Spider, robot, or bot automatically builds database
Index on a few keywords
Index on all words on web page
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Processing Requests
Search Engine Limitations
Index only a fraction of the Web
Approximately 20% to 33% of sites
More web pages added daily
Solution
Same request to several search engines
Metasearch
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Search Tools
Directories Search Engines
Yahoo! AltaVista
NetGuide Excite
Google
Metasearch Sites HotBot
MetaCrawler Infoseek
Dogpile Lycos
Northern Light
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Refine the Search
Add words
Enclose words in “quotes”
Use Boolean logic
Examples
“World Trade Center”
Jordan AND NOT Michael
Jordan -Michael
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Other Uses of the Internet
Streaming media
Instant messaging
Newsgroups
FTP
Telnet
E-mail
Internet Relay Chat (IRC)
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Streaming
Hear and see digitized content as it is
downloaded
Audio
Video
Animation
Uses substantial bandwidth
Quality of content
Speed of connection
Internet traffic
Performance will improve as bandwidth improves
Content is displayed using Plug-ins
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Instant Messaging
An IM conversation occurs in a small window
(rectangular area containing a document or
activity) on each participant’s display screen.
Instant messaging (IM) - allows any
user on a given e-mail system to send
a message and have it pop up
instantly on the screen of anyone else
logged onto that system
Lack of common standards
Time wasters when you have to get work done
Other participant may be a very slow typist
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Newsgroups / Usenet
Large bulletin board divided by category
Posting and reading of messages that
focus on specific topics
Over 20,000 newsgroups
Functions
Conversation
File download
Newsreader software required (included
with most browsers)
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Newsgroup Operations
Lurking
Posting material
Inappropriate material
Flame
Flame war
Moderated newsgroup
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FTP
File Transfer Protocol
Download files to your local computer
Upload files to another computer
Requirements to download file
Permission to download from a site
File is available for copying
Anonymous FTP – do not need to identify
yourself to the remote computer
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Download/Upload
Download - to transmit
data from a remote
computer to a local
computer
Upload - to transmit data
from a local computer to
a remote computer
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Telnet
Use your PC as a terminal providing
remote access to another computer
Permits
Log on to a host
Use as if you are sitting at a local terminal
Need account on the host system
Telnet software required (provided with
most browsers)
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e-mail
Send/receive written messages
Most used feature of the Internet
Mail server – Collects and stores e-mail
Mailbox – Assigned to each user
E-mail address
User name
@
Domain of the mail server
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Sending & Receiving E-Mail
E-Mail Software & Carriers
Find (Buy!) e-mail software
Get e-mail program as part of
other computer software
(such as browser)
Get e-mail software as part of
your ISP package
Get free e-mail services
How many of you have a free e-
mail account? What are its
advantages? What are its
disadvantages?
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E-Mail Addresses
A_hashemi@ce.aut.ac.ir
User name: A_hashemi
Computer name : ce
Domain name: aut
Top-level domain: .ac
Two-letter country extension: .ir
Domain - a location on the Internet.
Tips about e-mail addresses:
Type addresses carefully
Use the “reply” command when responding
Use the “address book” feature
Deal with each e-mail reply only once
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Mailing Lists
Mailing Lists:
E-Mail Based Discussion Groups
List-serves
e-mail mailing lists of people who
regularly participate in discussion
groups
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e-mail
Client Software Functions
Retrieve
Send
Create
Store
Print
Delete
Address book
Attach files
Filters
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…
Spam: Unwanted Junk E-Mail
Spam - unsolicited e-mail in the form of
advertising or chain letters.
Delete without opening the message
Never reply to a spam message!
Enlist the help of your ISP or use spam
filters
Fight back
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Problems
Useless web sites
Misinformation and misstatements on
web sites
Concern over government censorship
Multiple website on ONE server with ONE IP!
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Social Issues
Behavior problems
Who is out there?
What are they doing?
Netiquette
Suggestions for appropriate behavior
Example: TYPING IN CAPS is shouting
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Netiquette: Appropriate Online
Behavior
Consult FAQs Avoid flaming Don’t SHOUT!
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Netiquette: Appropriate Online
Behavior
Avoid sloppiness but avoid criticizing
others’ sloppiness
Don’t send huge file attachments,
unless requested
When replying, quote only the
relevant portion!
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Any Question?
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