Transcript Internet

‫گارگاه کامپيوتر‬
‫‪The Internet & the World‬‬
‫‪Wide Web‬‬
‫)‪(concepts‬‬
‫تهيه كننده‪ :‬علي برادران هاشمي‬
ARPANet
Advanced Research Projects Agency Network
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1969 – US Department of Defense and
Rand Corporation
Origins
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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
ARPANet
Transmitting the Message
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Messages divided into packets
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TCP/IP protocol
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TCP – does the packeting and
reassembling of the message
IP – handles the addressing
ARPANet
Expands Beyond the Military
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Research computers from universities
Defense contractors
Needed technical expertise to work on
Internet
Tim Berners-Lee
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1990
Perceived a spider’s web of computers
with links from computer to computer
CERN site
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Easy movement due to links
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Dr. Berners-Lee’s physics laboratory
Birthplace of the World Wide Web
Hypertext
Hyper-region
Marc Andreessen
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1993
Created browser software
Mosaic – first browser
Provided attractive images and a
graphical interface permitting users to
click on pictures as well as text
ARPANet to Internet
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TCP/IP software is public domain
Network became more valuable as it
embraced other networks
ARPANet disappears
Internet Explosion
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Mid 1990s
Estimate over 333 million users
worldwide
Part of our daily lives
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Four factors
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TCP/IP standard
Ability to link from site to site
Ease of use of browser
Growth of PC and LANs that can connect
URL
Uniform Resource Locator
http://domain-name.top-level-domain/last-section
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Unique address of a web page or file on the
Internet
Case-sensitive
http
hypertext transfer protocol
http://domain-name.top-level-domain/last-section
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Protocol – rules
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Communication using links
Domain name
http://domain-name.top-level-domain/last-section
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Address of the ISP
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Domain names are registered
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Ongoing fee is paid for each domain
name
Top-level Domain
Represent the purpose of the organization of
entity
.com
.gov
.edu
.org
.net
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May be a two-letter country code (.ir)
Last section
http://domain-name.top-level-domain/last-section
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Directories and file names that specify a
particular web page
URL (Universal Resource Locator)
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URLs--addresses for web pages
http://www.aut.ac.ir/departments/index.htm
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Protocol : http://
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Protocol - a set of communication rules for exchanging
information.
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Domain name: aut.ac.ir
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Directory name: departments
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File name: index.htm
Getting Started
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Computer with a modem or NIC
Internet service provider (ISP)
Browser
Related software
Internet Service Provider
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Vehicle to access the Internet
Provides
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Server computer
Software to connect
Choosing Your Internet Access
Device & Physical Connection
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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
Transmission speeds
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Transmission speeds:
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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.”
Telephone (Dial-Up) Modem: Low Speed
but Inexpensive & Widely Available
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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.
High-Speed Phone Lines: More
Expensive but Available in Most Cities
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ISDN - hardware and software that allows
voice, video, and data to be communicated over
traditional copper-wire telephone lines
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DSL - also uses regular phone lines but much
faster than ISDN
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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
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128 Kbps
T1 - 1.5 Mbps
Generally used by corporate, government, & academic
sites.
Cable modem
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Cable Modem: Close Competitor to
DSL
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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
Choosing Your Internet Service
Provider (ISP)
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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
Wireless Internet Access
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Supports mobile handheld devices
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Applications
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Text pagers
PDAs
Pocket computers
Web-enabled cellular phones
E-mail
Checking weather
Making airline reservations
Wireless Internet Access
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Need
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Wireless Application Protocol (WAP)
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Account with wireless access provider
Cellular modem card or adapter
Convert web pages into format for mobile
devices
Resized for limited display area
Fewer graphics transmitted
Slow download speeds
The World Wide Web
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Q: What makes
the Web
graphically
inviting?
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Q: What makes
the Web easily
navigable?
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A: Multimedia
A: Hypertext
The World Wide Web (Cont.)
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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
other multimedia documents.
The Web & How It Works
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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
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Web pages--the documents on a website
Web page - a document on the WWW that can include
text, pictures, sound, and video
Browser
Netscape Communicator
Microsoft Internet Explorer (IE)
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Browser
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Used to explore the Internet
Display web pages
Browser
Functions and Features
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Browser display window
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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
Browser
Functions and Features
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Welcome banner on title bar
Browser logo – animation indicates you are in
the process of moving to a new site
Hot list
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Bookmark
Favorites
Store your favorite URLs
Browser control panel – menus and buttons
Browser
Menus and Buttons
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Pull-down menu
Buttons
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Convenient shortcuts for commonly used
functions
Click button rather than locate command
from pull-down menu
Browser Support
Frames
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Divides page into rectangular sections
Each section displays web pages
independently
Several small pages on one screen
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Can be scrolled independently
Can be replaced with other pages independently
Plug-ins
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Software that increases the functionality
of a browser
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Download from web sites
Install
Example
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Audio-video
Image viewing
Adobe Acrobat Reader
Shockwave
Programming
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ActiveX Controls
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Capabilities similar to Java
Browser must be enabled to support
applets / ActiveX Controls
Security issues
Moving Between Sites
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Clickable categories in the browser
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Sports
Weather
News
Technology
Comic strips
Enter the URL in the address text box and
press <Enter>
Processing Requests
URL
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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)
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
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Search Engine builds database
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Searchable terms
Related web sites
Spider, robot, bot
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Follows links across the web
Automatically indexes pages to a database
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One word
All words
Pages may be submitted by the owner
Processing Requests
Search Engine Database (Cont.)
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Request same search using different
engines yields different results
Databases built independently
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Size
Content
Search methodology
Metasearch – atomically puts the same
request to several search engines
Processing Requests
Directory vs. Search Engine
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Directory
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Search Engine
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Human involvement!
Sites organized by content category
May concentrate on specific content areas
Subjective decisions regarding inclusion and
importance
Spider, robot, or bot automatically builds database
Index on a few keywords
Index on all words on web page
Processing Requests
Search Engine Limitations
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Index only a fraction of the Web
Approximately 20% to 33% of sites
More web pages added daily
Solution
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Same request to several search engines
Metasearch
Search Tools
Directories
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Yahoo!
NetGuide
Search Engines
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Metasearch Sites
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MetaCrawler
Dogpile
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AltaVista
Excite
Google
HotBot
Infoseek
Lycos
Northern Light
Refine the Search
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Add words
Enclose words in “quotes”
Use Boolean logic
Examples
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“World Trade Center”
Jordan AND NOT Michael
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Jordan -Michael
Other Uses of the Internet
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Streaming media
Instant messaging
Newsgroups
FTP
Telnet
E-mail
Internet Relay Chat (IRC)
Streaming
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Hear and see digitized content as it is
downloaded
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Audio
Video
Animation
Uses substantial bandwidth
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Quality of content
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Speed of connection
Internet traffic
Performance will improve as bandwidth improves
Content is displayed using Plug-ins
Instant Messaging
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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
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Lack of common standards
Time wasters when you have to get work done
Other participant may be a very slow typist
Newsgroups / Usenet
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Large bulletin board divided by category
Posting and reading of messages that
focus on specific topics
Over 20,000 newsgroups
Functions
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Conversation
File download
Newsreader software required (included
with most browsers)
Newsgroup Operations
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Lurking
Posting material
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Inappropriate material
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Flame
Flame war
Moderated newsgroup
FTP
File Transfer Protocol
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Download files to your local computer
Upload files to another computer
Requirements to download file
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Permission to download from a site
File is available for copying
Anonymous FTP – do not need to identify
yourself to the remote computer
Download/Upload
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Download - to transmit
data from a remote
computer to a local
computer
Upload - to transmit data
from a local computer to
a remote computer
Telnet
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Use your PC as a terminal providing
remote access to another computer
Permits
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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)
e-mail
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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
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User name
@
Domain of the mail server
Sending & Receiving E-Mail
E-Mail Software & Carriers
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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 email account? What are its
advantages? What are its
disadvantages?
E-Mail Addresses
[email protected]
User name: A_hashemi
Computer name : ce
Domain name: aut
Top-level domain: .ac
Two-letter country extension: .ir
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Tips about e-mail addresses:
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Domain - a location on the Internet.
Type addresses carefully
Use the “reply” command when responding
Use the “address book” feature
Deal with each e-mail reply only once
Mailing Lists
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Mailing Lists:
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List-serves
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E-Mail Based Discussion Groups
e-mail mailing lists of people who
regularly participate in discussion
groups
e-mail
Client Software Functions
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Retrieve
Send
Create
Store
Print
Delete
Address book
Attach files
Filters
…
Spam: Unwanted Junk E-Mail
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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
Problems
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Useless web sites
Misinformation and misstatements on
web sites
Concern over government censorship
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Multiple website on ONE server with ONE IP!
Social Issues
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Behavior problems
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Netiquette
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Who is out there?
What are they doing?
Suggestions for appropriate behavior
Example: TYPING IN CAPS is shouting
Netiquette: Appropriate Online
Behavior
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Consult FAQs
Avoid flaming
Don’t SHOUT!
Netiquette: Appropriate Online
Behavior
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Avoid sloppiness but avoid criticizing
others’ sloppiness
Don’t send huge file attachments,
unless requested
When replying, quote only the
relevant portion!
Any Question?
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