WWW11 World Wide Web 1

WWW12 Networks allow computers to talk to each other

WWW13 Networks can have different topologies Linear Star

WWW14 If a node on a network fails other nodes might be disconnected

WWW15 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

WWW16 A network with a center would be very vulnerable to attach

WWW17 A distributed network with multiple routes between points would be more likey to survive

WWW18 The network relied on the ability of the nodes to dynamically find routes for data

WWW19 The Internet The result was a global decentralized network that no one owns.

WWW110 Network Protocols 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

WWW111 Hyper Text Transfer Protocol HTTP allowed information for public consumption to be transferred and read easily HyperText Markup Language was developed for describing the content

WWW112 What happens when you look at a web page? Browser Link Network Server HTML file Network Image file Browser

WWW113 Browser Web pages are displayed in a browser Common Browsers –Internet Explorer (MS) –Navigator (Netscape) –Opera –Safari (Apple) –Firefox

WWW114 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

WWW115 Network The URL request for data is routed through the internet until it finds its way to the web server

WWW116 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

WWW117 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

WWW118 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

WWW119 Browser The browser lays out the web page with images as specified by the HTML Different browsers might render the HTML slightly differently

WWW120 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

WWW121 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

WWW122 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

WWW123 H.T.M.L. Web pages are written Hypertext Mark up Language HTML pages are ASCII text files with tags for formatting

WWW124 HTML Example: 1 Basic Page Tags are bounded by Tags usually occur in pairs All of the content appears in the body Hello World

WWW125 HTML Example 2: Bold & Italics Hello World Howdy Doody Hello World Howdy Doody N

WWW126 HTML Example 3: A Link Hello World Howdy Doody CIT Hello World Howdy Doody CIT N

WWW127 More Examples on Handouts