April 17, 2004 April 17, 2004 Prof. Paul Lin Prof. Paul Lin 1 CPET 355 CPET 355 Data Communications & Data Communications & Networking Networking 7. The Application Layer: 7. The Application Layer: World Wide Web - Part 1 World Wide Web - Part 1 Paul I-Hai Lin, Professor Paul I-Hai Lin, Professor Electrical and Computer Engineering Electrical and Computer Engineering Technology Technology Purdue University, Fort Wayne Campus Purdue University, Fort Wayne Campus
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7. The Application Layer:7. The Application Layer:World Wide Web - Part 1World Wide Web - Part 1
Paul I-Hai Lin, Professor Paul I-Hai Lin, Professor Electrical and Computer Engineering Electrical and Computer Engineering
TechnologyTechnologyPurdue University, Fort Wayne CampusPurdue University, Fort Wayne Campus
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The World Wide WebThe World Wide Web
The Web began in 1989 at CERN, the The Web began in 1989 at CERN, the European center for nuclear researchEuropean center for nuclear research
Tim Berners-Lee, a CERN physicist Tim Berners-Lee, a CERN physicist proposed “A Web of Linked Documents,” proposed “A Web of Linked Documents,” in 1989 for distributing/sharing high-energy in 1989 for distributing/sharing high-energy physics data: reports, blueprints, drawings, physics data: reports, blueprints, drawings, photos, and other documentsphotos, and other documents
In Dec. 1991, the first text-based prototype In Dec. 1991, the first text-based prototype was demonstrated in An Antonio, Texaswas demonstrated in An Antonio, Texas
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The World Wide WebThe World Wide Web
Marc Andreessen at the U. of Illinois, Marc Andreessen at the U. of Illinois, developed the first GUI based browser, developed the first GUI based browser, Mosaic and released in Feb. 1993Mosaic and released in Feb. 1993
Marc Andreessen form a company – Marc Andreessen form a company – Netscape Communications Corp., to Netscape Communications Corp., to develop clients, servers, and Web develop clients, servers, and Web software and went public in 1995software and went public in 1995
In 1998, AOL bought Netscape for $4.2 In 1998, AOL bought Netscape for $4.2 billionsbillions
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The World Wide WebThe World Wide Web
In 1994, CERN and MIT signed and In 1994, CERN and MIT signed and agreement setting up the World Wide Web agreement setting up the World Wide Web Consortium (Consortium (www.w3c.orgwww.w3c.org))
Time Berners-Lee became the director of Time Berners-Lee became the director of W3CW3C
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WWW ArchitectureWWW Architecture
The Web - consists of a vast, worldwide The Web - consists of a vast, worldwide collections of Web pages (documents) stored in collections of Web pages (documents) stored in Web serversWeb servers
Web pages Web pages • Text files written in HTML (HyperText Markup Text files written in HTML (HyperText Markup
Language), and saved with htm or html as an Language), and saved with htm or html as an extensionextension
• Each page may contain links to other pages Each page may contain links to other pages anywhere in the worldanywhere 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
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Browser <-> DNS <-> IP addressBrowser <-> DNS <-> IP address Browser makes a TCP connection to the port 80 on Browser makes a TCP connection to the port 80 on
this IP addressthis IP address Request for the index.html page from the Web Request for the index.html page from the Web
serverserver The Web server sends index.html and related The Web server sends index.html and related
image filesimage files Disconnect TCP connectionDisconnect TCP connection Display all the text and imagesDisplay all the text and images
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Web ClientsWeb Clients
HTML InterpreterHTML Interpreter Javacript InterpreterJavacript Interpreter Built-in MIME TypeBuilt-in MIME Type FTP InterfaceFTP Interface Plug-in – a code module that installed Plug-in – a code module that installed
when needed (Java plug-in for example)when needed (Java plug-in for example) Helper applications (Adobe Acrobat Helper applications (Adobe Acrobat
Reader for displaying PDF files, or MS Reader for displaying PDF files, or MS Word for displaying DOC files)Word for displaying DOC files)
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Web ServersWeb Servers
Web serversWeb 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 Retrieve the requested file from the server’s
diskdisk• Process the needed server procedures or Process the needed server procedures or
