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World Wide Web 1

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 Wide Web 1

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  1. World WideWeb 1 WWW1

  2. Networks allow computers to talk to each other WWW1

  3. Networks can have different topologies Linear Star WWW1

  4. If a node on a network fails other nodes might be disconnected WWW1

  5. 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 WWW1

  6. A network with a center would be very vulnerable to attach WWW1

  7. A distributed network with multiple routes between points would be more likey to survive WWW1

  8. The network relied on the ability of the nodes to dynamically find routes for data WWW1

  9. The result was a global decentralized network that no one owns. The Internet WWW1

  10. 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 WWW1

  11. 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 WWW1

  12. What happens when you look at a web page? • Browser • Link • Network • Server • HTML file • Network • Image file • Browser WWW1

  13. Browser • Web pages are displayed in a browser • Common Browsers • Internet Explorer (MS) • Navigator (Netscape) • Opera • Safari (Apple) • Firefox WWW1

  14. 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 WWW1

  15. Network • The URL request for data is routed through the internet until it finds its way to the web server WWW1

  16. 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 WWW1

  17. 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 WWW1

  18. 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 WWW1

  19. Browser • The browser lays out the web page with images as specified by the HTML • Different browsers might render the HTML slightly differently WWW1

  20. 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 WWW1

  21. 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 WWW1

  22. 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 WWW1

  23. H.T.M.L. • Web pages are written Hypertext Mark up Language • HTML pages are ASCII text files with tags for formatting WWW1

  24. 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 WWW1

  25. Hello World HowdyDoody <html> <head></head> <body> Hello World<br/> <b>Howdy</b><i>Doody</i> </body> </html> HTML Example 2: Bold & Italics N WWW1

  26. 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 WWW1

  27. <b><i><u> <br/> <hr/> <a href=“”> <img src=“”/> <tt><code> More Examples on Handouts WWW1

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