Dr. Jim Martin jim.martin@cs.clemson.edu The World Wide Web Dr. Jim Martin jim.martin@cs.clemson.edu Clemson’s Emerging Scholars Partnership, Summer 2005
The World Wide Web Clemson Southside High School Internet Web browser: A client program Dialup connection 117A Clemson Southside High School Internet Access Network (Internet Service Provider or ISP) Server Room The Internet is made up of separate networks that can communicate with each other. TCP/IP the ‘magical’ networking software (a protocol) that enables your browsing experience from home, high school or Clemson to be identical. www.usatoday.com www.cs.clemson.edu Web servers: A server program Clemson’s Emerging Scholars Partnership, Summer 2005
What is a protocol? A specification for a set of message exchanges Computer protocols: much more precise rules. For example, getting the base web page from a web server Human protocols: conventions used to accomplish a task. For example, mailing a letter 1.Create the letter 2.Package it 3.Address it and add postage 4.Send it Time Open a connection US Postal System Issues: — Errors: Planned for errors (“function not implemented,” “service unavailable”), and unexpected errors (message corrupted). — Lack of a response (“timeout”). Acknowledge the connection Request the file 1.Receive the letter 2.Rip it open 3.Read it Send the file
Web browsers and servers Web browser: A client program Internet www.usatoday.com This interaction might take less than 1 millisecond or it might take 10 seconds. It depends on: Speed of the connections How busy the server is Client program sends a packet of data that contains the command: Get me this web page Server program replies by sending a variable number of packets That collectively contain the web page Computers break the data into packets which are usually 1500 Bytes large Client program assembles the web page from the received packets and displays the page, it Then sends an ACK packet to the server saying it received the page.
Web browsers and servers Web browser: A client program Internet www.usatoday.com The rules for that the client and server follow to transfer web pages are defined by HTTP: Hypertext Transport Protocol. The rules that Web Pages must follow are defined by HTML: Hypertext Markup Language
HTML <html> <head> <title> Hi welcome to Dr Martin's web page !!!! </title> </head> <body> <hr> <div align="Center"> <h1> Dr. Jim Martin's Web Page </h1> </div> <br> <p>This is a paragraph block. </p> <h2>There are up to 9 levels of section headings. <h3>Section heading 3 </h3> </h2> <p> To have a link in your web page, there are two pieces of information that you need in the tag line. First, the href is the actual link pointer. This must be the full pointer that includes the actual file name. Second, you need to add the name of the link that will be displayed. In the example below, the link is to webmonkey.wired.com. The page will just show Web Monkey. <a href="http://webmonkey.wired.com/webmonkey/kids/meta/powered.html"> Web Monkey</a> </p> </body> </html>
Exercise Create a file (index.html) using notepad Cut and paste the previous html code into your file Save your file and open with a browser Start a browser and select File and then Open File Extend the page (refer to “A Beginner’s Guide to HTML”): Create a list of pointers to your 3 favorite web sites (please nothing nasty!!!) Add to your page the paw.gif image available from the class web site