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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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World WideWeb 1

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Networks allow computers to talk to each other
Networks allow computers to talk to each other

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Networks can have different topologies
Networks can have different topologies

Linear

Star

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The internet
The Internet disconnected

  • 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 owns.

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 owns.

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? owns.

  • Browser

  • Link

  • Network

  • Server

  • HTML file

  • Network

  • Image file

  • Browser

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Browser
Browser owns.

  • Web pages are displayed in a browser

  • Common Browsers

    • Internet Explorer (MS)

    • Navigator (Netscape)

    • Opera

    • Safari (Apple)

    • Firefox

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Link owns.

  • 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 owns.

  • 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 owns.

  • 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 owns.

  • 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 owns.

  • 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 owns.

  • 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 owns.

  • 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 owns.

  • 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 owns.

  • 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. owns.

  • 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 > owns.

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 owns.

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 owns.

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> owns.

<br/> <hr/>

<a href=“”>

<img src=“”/>

<tt><code>

More Examples on Handouts

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