April 17, 2004 Prof. Paul Lin 1 CPET 355 Data Communications & Networking 7. The Application Layer: World Wide Web - Part 1 Paul I-Hai Lin, Professor Electrical and Computer Engineering Technology Purdue University, Fort Wayne Campus

April 17, 2004 Prof. Paul Lin 2 The World Wide Web The Web began in 1989 at CERN, the European center for nuclear research The Web began in 1989 at CERN, the European center for nuclear research Tim Berners-Lee, a CERN physicist proposed “A Web of Linked Documents,” in 1989 for distributing/sharing high-energy physics data: reports, blueprints, drawings, photos, and other documents Tim Berners-Lee, a CERN physicist proposed “A Web of Linked Documents,” in 1989 for distributing/sharing high-energy physics data: reports, blueprints, drawings, photos, and other documents In Dec. 1991, the first text-based prototype was demonstrated in An Antonio, Texas In Dec. 1991, the first text-based prototype was demonstrated in An Antonio, Texas

April 17, 2004 Prof. Paul Lin 3 The World Wide Web Marc Andreessen at the U. of Illinois, developed the first GUI based browser, Mosaic and released in Feb Marc Andreessen at the U. of Illinois, developed the first GUI based browser, Mosaic and released in Feb Marc Andreessen form a company – Netscape Communications Corp., to develop clients, servers, and Web software and went public in 1995 Marc Andreessen form a company – Netscape Communications Corp., to develop clients, servers, and Web software and went public in 1995 In 1998, AOL bought Netscape for $4.2 billions In 1998, AOL bought Netscape for $4.2 billions

April 17, 2004 Prof. Paul Lin 4 The World Wide Web In 1994, CERN and MIT signed and agreement setting up the World Wide Web Consortium ( In 1994, CERN and MIT signed and agreement setting up the World Wide Web Consortium ( Time Berners-Lee became the director of W3C Time Berners-Lee became the director of W3C

April 17, 2004 Prof. Paul Lin 5 WWW Architecture The Web - consists of a vast, worldwide collections of Web pages (documents) stored in Web servers The Web - consists of a vast, worldwide collections of Web pages (documents) stored in Web servers Web pages Web pages Text files written in HTML (HyperText Markup Language), and saved with htm or html as an extensionText files written in HTML (HyperText Markup Language), and saved with htm or html as an extension Each page may contain links to other pages anywhere in the worldEach page may contain links to other pages anywhere in the world User can follow a link by clicking on itUser can follow a link by clicking on it This process can be repeated indefinitelyThis process can be repeated indefinitely

April 17, 2004 Prof. Paul Lin 6 Web Browser Architecture

April 17, 2004 Prof. Paul Lin 7 Web Clients Address - URLs (uniform resource locators) Address - URLs (uniform resource locators) Browser DNS IP address Browser DNS IP address Browser makes a TCP connection to the port 80 on this IP address Browser makes a TCP connection to the port 80 on this IP address Request for the index.html page from the Web server Request for the index.html page from the Web server The Web server sends index.html and related image files The Web server sends index.html and related image files Disconnect TCP connection Disconnect TCP connection Display all the text and images Display all the text and images

April 17, 2004 Prof. Paul Lin 8 Web Clients HTML Interpreter HTML Interpreter Javacript Interpreter Javacript Interpreter Built-in MIME Type Built-in MIME Type FTP Interface FTP Interface Plug-in – a code module that installed when needed (Java plug-in for example) Plug-in – a code module that installed when needed (Java plug-in for example) Helper applications (Adobe Acrobat Reader for displaying PDF files, or MS Word for displaying DOC files) Helper applications (Adobe Acrobat Reader for displaying PDF files, or MS Word for displaying DOC files)

April 17, 2004 Prof. Paul Lin 9 Web Clients Client’s MIME type/subtype Client’s MIME type/subtype Text/htmlText/html application/pdfapplication/pdf application/mswordapplication/msword image/gifimage/gif Image/jpgImage/jpg image/x-photoshopimage/x-photoshop audio/mp3 - RealOne playeraudio/mp3 - RealOne player

April 17, 2004 Prof. Paul Lin 10 Web Servers Web servers Web servers Listen to TCP port 80Listen to TCP port 80 Accept client connections (browsers)Accept client connections (browsers) Retrieve the requested file from the server’s diskRetrieve the requested file from the server’s disk Process the needed server procedures or functions (authentication, cookies, session, access control, log, etc)Process the needed server procedures or functions (authentication, cookies, session, access control, log, etc) Return the fileReturn the file Release the TCP connectionRelease the TCP connection

April 17, 2004 Prof. Paul Lin 11 An Apache Web Server Example

April 17, 2004 Prof. Paul Lin 12 Web Servers

April 17, 2004 Prof. Paul Lin 13 TCP/IP-Based Remote Control

April 17, 2004 Prof. Paul Lin 14 TCP/IP-based-Monitoring and Control