Transcript COMM 1213 H1 COMP 4923 X1

COMM 1213 H1
COMP 4923 X1
The Internet and the Web
(Readings: Ch. 1 & 2 of C.D.Knuckles)
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Outline
• Technologies that we will cover
• The Internet and its components
• The Web and its components
• Webpages and their publication on the
web
• Knowledge versus Information (optional)
EG
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Internet and Web Technology
URL TCP/IP
Browsers
Servers
HTML
HTTP
SQL
Database
Java
Cookies
CGI
SMTP
Wireless
Applets
FTP
POP
MIME
Smart Cards
e-Payment
Servlets
Authentication
Encryption
SSL
JSPs
XML
DW/DM
Pervasive
Computing
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Technologies that we will cover
in the course
• Basic Web components:
– Internet, Web, Browsers, Servers, HTTP, SSL
• Data types (text, image, video, audio)
• HTML
• Fundamentals of programming
• JavaScript
DS
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History of the Internet
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•
1969
1997
1984
1987
1989
1992
2006
ARPANET – 4 systems connected
– 25 systems connected
NSFNET – 1000 servers, IPM PC arrives
– 10,000 servers connected
– 100,000 servers connected
– 1,000,000 servers connected
– estimated at 100,000,000 servers
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E-Commerce Growth
The Driving Force The Internet Economy
• To reach 50,000,000 users
– Radio took 38 years
– Computers took over 16 years
– TV took 13 years
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•
– The Internet took 4 years!
Over 75% of (12.3M)Canadian homes now have PCs
Over 55% (6.7M) of those are Internet connected, up
51% over 2002
• Sources:
•
http://www.cbc.ca/stories/2004/07/08/canada/computer
_use040708
CBC, Forrester
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Internet Economy Global Growth
Sales
(billions)
$3,000
1998 – 111M users
2000 – 320M users
2005 – 720M users
$3.2T
$2,000
$1,000
Hyper-growth
begins
$150B
0
1998
1999
2000
2001
2002
2003
$80
$170
$390
$970
$2,000
$3,200
Source: Forrester
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The Internet and its components
• How is data transmitted around the globe?
– Transmission media types?
• Digital versus analog communications
• What does it mean to have higher
bandwidth?
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The Client-Server Model
• Client – a machine that makes Internet
•
•
requests for resources (printing, data,
processing)
Server – a machine that performs tasks for
clients on request and manages network
resources
Communications protocol – a set of rules for
two or more entities to converse
Client
Comm.
Protocol
Server
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What is an internet?
• Communication between two or more
potentially heterogeneous networks
(LANs)
• The “Internet” is a set of standards for
inter-network communications
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Architectural of the Internet
Acadia
Client 1
Application
Client 2
Server X
TCP/IP
Internet
Application
Intrane
t
Server Y
Server C
Server B
Server C
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TCP/IP Protocol Architecture
Transmission Control Protocol
Internet Protocol
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TCP/IP Protocol Architecture
• Internet Protocol (IP) – like a postcard
that contains:
– Destination address (131.162.201.7)
– Return address
– Block of data (content)
• Transmission Control Protocol (TCP)
– Ensures the post card gets through
– Ensures the order of deliver
– Handles errors and control flow
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Client-Server Applications that
use the Internet
Telnet Window
FTP Client
eMail Client
TCP
IP
Network
Physical
Telnet Protocol
FTP
SMTP/POP
Internet
Telnet Server
FTP Server
eMail Server
TCP
IP
Network
Physical
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Architecture of the Internet
• What is an IP address
– Of the form 255.255.255.255
• (32 bit address)
– Acadia’s IP address is what?
• 131.162.200.72
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Traffic on the Internet
• Packets and multiple paths
• Routers (demo with 4 students)
– Sending server, two routers and a receiving
client
– Play out the request and response for a file
• What happens if a packet is lost?
– Only that packet needs to be retransmitted
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What is the Web?
• A class of applications that use the
Internet plus a lot of new technologies
and standards that facilitate access to
resources managed by servers connected
to the Internet:
– Hardware: Servers
– Software: Browsers, Servers
– Protocols: HTTP, HTML, MIME
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Major Architectural Components
of the Web
Client 1
Browser
Client 2
HTTP
TCP/IP
Internet
Browser
Server A
HTTP
Server
App.
Server
Database
Server
URL index.html
Server B
Server C
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The Web and its components
• Tower babble on the Internet
– Mix of computers, operating systems, applications and data
formats
– Required a lot of special knowledge to acces information
– ftp, telnet, news, mail, file
• URL – Universal Resource Locator
– How://Where/What
– http://plato.acadiau.ca/courses/comp/dsilver/4923/
– ftp://plato.acadiau.ca
– file://C:\Documents and Settings\dsilver\My Documents
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Named Addresses and Domains
• http://131.162.200.72 is too difficult to remember, so a
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naming systems was conceived …
http://www.acadiau.ca
Domain names have advantages:
– Easier market; Not case sensitive
– One IP can have several domain names
• How are domain names resolved?
– Domain Name Server (DNS)
• How are they established?
– Registration service
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Finding out about domain names
– http://www.keytlaw.com/urls/whoowns.htm
– http://www.hcidata.co.uk/host2ip.htm
• Does someone own your domain name?
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WWW and Platform Independence
• Definition: An application is a software program
• Written for a particular operating system
– MS Windows, Apple Mac, Linux, Unix
– Windows programs will not run on a Mac
– They are platform dependent
• In contrast, browsing the web is platform
•
independent
So are browsers platform independent?
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ASCII Text files
• Open the window Notepad application
• Type “This is a simple text file.”
• Close and save the file as simple.html on
your desktop
• We will use this to build our first series
web pages .. because web pages are
written in ASCII text
• Click on simple.html on your desktop
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Stay away from MS Word!
• TRY-IT: Compare simple.html with a Word
file simple.doc opened with Notepad
• Don’t use Word for simple text or HTML
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How did simple.html become a
webpage?
• The browser is smart enough to recognize
that this is not really HTML so defaults to
displaying ASCII text
But how do we get it on a server?
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Public Directories and Web Servers
• Requires an account on a computer connected
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to the Internet that is web server ready
Computer accounts have an associated
– Root directory such as “dsilver” or “066525m”
– User/password such as “066525m/secret”
• Do you have an account on such a server at
Acadia?
– Try: http://axe.acadiau.ca/
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Your account and website at Acadia
• Open My Computer and look for something like:
– 066525m on ‘Axe\Dat\User\Cstudent’ (H:)
– While connected to the network drive H
on you computer is linked to your Axe
Server and your root directory
• If you do not see this then:
– Find the read “N” in the Windows tray at the bottom
– Right click and choose “Network Login …”
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Your account and website at Acadia
• Let’s put something on the web:
– By convention web files must be placed in a subdirectory called
“WWW”
– Create this subdirectory using File/New from the My Computer
window
– Just copy and paste simple.html from your desk top into WWW
• Let’s view it:
Yours: http://axe.acadiau.ca/~066525m/simple.html
Mine:
http://ace.acadiau.ca/~dsilver/simple.html
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Hiding Web Directories
• Normally you do not wish web servers to see
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everything your web dircetory
Solution:
– Rename simple.html to index.html
– Now browse for
• http://axe.acadiau.ca/~066525m/simple.html
• http://ace.acadiau.ca/~dsilver/
• Why does this work?
– The server knows to look for index.html as a default
– No other files can be seen
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FTP Upload of a file
• FTP = File Transport Protocol (1980s)
– Put = upload to server
– Get = download from server
• You can download and install a free FTP
client to your computer call ws_ftp
• Demo of ws_ftp
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Internet Security Risks
• Downloading files to your computer is normally
•
•
not harmful
Opening or executing files can put your laptop at
risk when outside the browser
Examples:
– Files saved from your browser to the HD
– FTPed files
– Email attachments (spam)
• In genera, if you are uncertain of the
server/sender, do not open the file.
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How does a web page get from the
server to my browser?
• HTTP = Hyper Text Transport Protocol
• Key to Web technology
• Browser issues a “get” HTTP request for
– http://axe.acadiau.ca/~066525m/simple.html
– how://-----where-----/-------what---------------
• Internet delivers the request to Axe server using TCP/IP
• Axe server finds the simple.html file
• Axe server sends a HTTP response back to your laptop’s
IP address
• The page is then “cashed” in your browser’s temporary
memory and displayed
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HTTP
HyperText Transfer Protocol
The application protocol of the Web
 Like FTP it is layered on top of TCP/IP

Web Browser
TCP
IP
Network
Physical
HTTP
Internet
HTTP Server
TCP
IP
Network
Physical
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