CPET 355 Data Communications

1
CPET 355Data 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

2
The World Wide Web

• 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
• In Dec. 1991, the first text-based prototype was
  demonstrated in An Antonio, Texas

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The World Wide Web

• Marc Andreessen at the U. of Illinois, developed
  the first GUI based browser, Mosaic and released
  in Feb. 1993
• 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

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The World Wide Web

• In 1994, CERN and MIT signed and agreement
  setting up the World Wide Web Consortium
  (www.w3c.org)
• Time Berners-Lee became the director of W3C

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WWW Architecture

• The Web - consists of a vast, worldwide
  collections of Web pages (documents) stored in
  Web servers
• Web pages
• Text 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 world
• User can follow a link by clicking on it
• This process can be repeated indefinitely

6
Web Browser Architecture
7
Web Clients

• Address - URLs (uniform resource locators)
• http//www.etcs.ipfw.edu/lin/index.html
• Browser lt-gt DNS lt-gt 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
• The Web server sends index.html and related image
  files
• Disconnect TCP connection
• Display all the text and images

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Web Clients

• HTML Interpreter
• Javacript Interpreter
• Built-in MIME Type
• FTP Interface
• 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)

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Web Clients

• Clients MIME type/subtype
• Text/html
• application/pdf
• application/msword
• image/gif
• Image/jpg
• image/x-photoshop
• audio/mp3 - RealOne player

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Web Servers

• Web servers
• Listen to TCP port 80
• Accept client connections (browsers)
• Retrieve the requested file from the servers
  disk
• Process the needed server procedures or functions
  (authentication, cookies, session, access
  control, log, etc)
• Return the file
• Release the TCP connection

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An Apache Web Server Example
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Web Servers
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TCP/IP-Based Remote Control
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TCP/IP-based-Monitoring and Control