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World Wide Web 1. Networks allow computers to talk to each other. Networks can have different topologies. Linear. Star. If a node on a network fails other nodes might be disconnected. The Internet.

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Presentation Transcript
the internet
The Internet
  • During the Cold War the U.S. Military gave money to colleges and universities to develop networks that could survive a nuclear attack

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the network relied on the ability of the nodes to dynamically find routes for data
The network relied on the ability of the nodes to dynamically find routes for data

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network protocols
E-mail: allows users to send messages to each other

FTP: File Transfer Protocol

Telnet: allows users to log into their computers from remote locations

A number of network protocols were developed for the transfer of information

Network Protocols

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hyper text transfer protocol
Hyper Text Transfer Protocol

CERN

  • HTTP allowed information for public consumption to be transferred and read easily
  • HyperText Markup Language was developed for describing the content

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what happens when you look at a web page
What happens when you look at a web page?
  • Browser
  • Link
  • Network
  • Server
  • HTML file
  • Network
  • Image file
  • Browser

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browser
Browser
  • Web pages are displayed in a browser
  • Common Browsers
    • Internet Explorer (MS)
    • Navigator (Netscape)
    • Opera
    • Safari (Apple)
    • Firefox

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slide14
Link
  • In the browser the user can
    • Click on a link in the current page
    • Type in the URL for a new page e.g www.cit.ie

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network
Network
  • The URL request for data is routed through the internet until it finds its way to the web server

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server
Server
  • The web server accepts requests from web surfers for files it holds.
  • Using the URL it determines who wants what and then goes away and gets it

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network1
Network
  • The file the web surfer requested is sent across the network to the surfer’s browser
  • When it arrives the browser interprets the HTML and lays out the page according to instructions

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image file
Image File
  • If the web page the user requested contains images then the browser sends a request to the server to the images
  • When these images arrive the browser can insert them into the page

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browser1
Browser
  • The browser lays out the web page with images as specified by the HTML
  • Different browsers might render the HTML slightly differently

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broken link
Broken Link
  • If the surfer requests a file that is not on the server then the web server cannot deliver it
  • This happens with mis-typed URLs
  • If a link points to a file that is not available then is is a broken link

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html files
HTML Files
  • HTML files are bog-standard unformatted text files
  • By convention HTML files on the web server are named with extensions .htm or .html
  • The URL must specify the server name and the precise location of the file in the directory system

abcde.html

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images
Images
  • While modern browsers can render a variety of image formats only GIF and JPEG are considered standard
  • GIF Graphics Interchange Format
  • JPEG Joint Photographic Experts Group
  • PNG

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h t m l
H.T.M.L.
  • Web pages are written Hypertext Mark up Language
  • HTML pages are ASCII text files with tags for formatting

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html example 1 basic page
Tags are bounded by < and >

Tags usually occur in pairs

All of the content appears in the body

<html>

<head></head>

<body>

Hello World

</body>

</html>

HTML Example: 1 Basic Page

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html example 2 bold italics
Hello World

HowdyDoody

<html>

<head></head>

<body>

Hello World<br/>

<b>Howdy</b><i>Doody</i>

</body>

</html>

HTML Example 2: Bold & Italics

N

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html example 3 a link
Hello World

HowdyDoody

CIT

<html>

<head></head>

<body>

Hello World<br/>

<b>Howdy</b><i>Doody</i><br/>

<a href=“http://www.cit.ie/”>CIT</a>

</body>

</html>

HTML Example 3: A Link

N

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more examples on handouts
<b><i><u>

<br/> <hr/>

<a href=“”>

<img src=“”/>

<tt><code>

More Examples on Handouts

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