The Internet and the World Wide Web

1
The Internet and the World Wide Web
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The Internet

• Internet
• Developed in the 1960s with US Department of
  Defense funding
• Originally for connecting few main computer
  systems (the ARPANET)
• Intended to allow computers to be shared
• Became clear that key benefit was allowing fast
  communication between researchers - email

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The Internet

• ARPAs goals
• Allow multiple users to send and receive info at
  same time
• Network operated packet switching technique
• Digital data sent in small packages called
  packets
• Packets contained data, address info,
  error-control info and sequencing info
• Greatly reduced transmission costs of dedicated
  communications lines
• Network designed to be operated without
  centralized control
• If portion of network fails, remaining portions
  still able to route packets

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The Internet

• Transmission Control Protocol (TCP)
• Name of protocols for communicating over ARPANET
• Ensured that messages were properly routed and
  that they arrived intact
• Organizations implemented own networks
• Used both for intra-organization and communication

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The Internet

• Huge variety of networking hardware and software
  appeared
• ARPA achieved inter-communication between all
  platforms with development of the IP
• Internetworking Protocol
• Current architecture of Internet
• Combined set of protocols called TCP/IP
• The Internet
• Limited to universities and research institutions
• Military became big user
• Next, government decided to access Internet for
  commercial purposes

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The Internet

• Internet traffic grew
• Businesses spent heavily to improve Internet
• Better service their clients
• Fierce competition among communications carriers
  and hardware and software suppliers
• Result
• Bandwidth of Internet increased tremendously
• Costs dropped quickly

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IETF

• The Internet Engineering Task Force (IETF,
  http//www.ietf.org)
• Proposes standards in Internet architecture in
  various areas such as routing, security,
  transport, etc.
• Under IETF, the Internet Assigned Numbers
  Authority (IANA, http//www.iana.org) serves as
  the registrar for mime types, port numbers, and
  IP addresses.

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The World Wide Web

• World Wide Web (WWW, the Web)
• Developed around 1989 to 1990 by Tim Berners-Lee
  at CERN.
• A global hypertext-based system for
  locating/viewing documents using the HTTP
  protocol
• HTML documents and other multimedia documents
• Billions of pages on the Web now, and the size is
  still growing

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Basic Web Terminology

• HTML Hypertext Markup Language
• Allow users to link to other documents
• HTTP Hypertext Transfer Protocol
• A protocol for transferring hypertext documents
  over the Internet. Usually at port 80.
• URL/URI Uniform Resource Locator/Uniform
  Resource Identifier
• An address to locate objects that are retrievable
  on the net.
• Web page
• a document on the Web
• Web site
• a set of documents, often on the same Web domain

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WWW Consortium (W3C)

• W3C (http//www.w3.org/)
• Founded in 1994 by Tim Berners-Lee
• Devoted to developing non-proprietary and
  interoperable technologies for the World Wide Web
  and making the Web universally accessible
• Standardization
• W3C Recommendations technologies standardized by
  W3C
• include Extensible HyperText Markup Language
  (XHTML), Cascading Style Sheets (CSS) and the
  Extensible Markup Language (XML)
• Document must pass through Working Draft,
  Candidate Recommendation and Proposed
  Recommendation phases before considered for W3C
  Recommendation

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WWW Consortium (W3C)

• W3C Structure
• 3 Hosts
• Massachusetts Institute of Technology (MIT)
• INRIA (Institut National de Recherche en
  Informatique et Automatique)
• Keio University of Japan
• 400 Members
• W3C Goals
• User Interface Domain
• Technology and Society Domain
• Architecture Domain and Web Accessibility
  Initiatives

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A Three-Tier Architecture for Web Applications
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A Three-Tier Architecture

• Information tier
• Referred to as data tier or bottom tier
• Maintains data for application
• Stores data in relational database management
  system
• e.g., Oracle, MS Access, files systems
• Middle tier
• Implements business logic and presentation logic
• Controls interactions between application clients
  and application data
• Acts as intermediary between data in information
  tier and application clients
• e.g., servlets, PHP, Perl, and other server-side
  scripting

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A Three-Tier Architecture

• Middle tier (cont.)
• Controller logic
• Processes client requests from top tier
• Retrieves data from database
• Presentation logic
• Processes data from information tier
• Presents content to client
• Business logic
• Enforces business rules
• Dictates how clients can access application data
  and how applications process data
• Ensures data validity before updating database

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A Three-Tier Architecture

• Client tier
• Referred to as top tier
• Applications user interface
• Users interact with application through user
  interface
• Interacts with middle tier to make requests and
  to retrieve data from information tier
• Displays data to user
• e.g., Flash, Applets, and client-side scripting
  like JavaScript and VBScript

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Web Servers

• Web servers
• Specialized software that responds to client
  requests by providing resources
• When users enter URLs into Web browsers, they
  request specific documents from Web server
• Map URLs to files on server and returns requested
  documents to client
• Communicate with client using HTTP
• Protocol for transferring requests and files over
  the Internet

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Web Servers

• Popular Web servers
• Apache (about 68.8 of Web sites)
• Windows (IIS, PWS) (about 20.9)
• Sun (about 3.14)
• Zeus (about 1.19)
• Web servers have different functionalities and
  support different server-side software/languages.

Source of data netcraft.com, December 2004
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Accessing Web Servers

• Requesting documents
• Must know machine name on which Web server
  resides
• Through local Web servers or remote Web servers
• Through domain name or Internet Protocol (IP)
  address
• Local Web server
• Resides on users machines
• Requests documents in two ways
• Machine name
• localhost or 127.0.0.1
• Host name and IP address that reference the local
  machine

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Accessing Web Servers

• Remote Web server
• Resides on different machines
• Domain name
• Represents group of hosts on Internet
• Combines with how name (www) and top-level domain
  to from fully qualified host name
• Top-level domain (TLD)
• Describes type of organization that owns domain
  name
• .com or .org
• Fully qualified host name
• Provides user friendly way to identify site on
  Internet

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IP Address

• IP address
• Unique address for locating computers on Internet
• Most of todays Internet use IP Version 4 (IPv4).
  More details can be found on http//www.networkso
  rcery.com/enp/protocol/ip.htm
• IPv4 allocates 32 bits for IP address (e.g.,
  147.8.210.1 each of the 4 numbers has 8 bits (0
  to 255).
• 232 1,073,741,824 1 billion. We are running
  out of IP addresses!
• The IETF has proposed the IP Version 6. IPv6
  allocates 128 bits for IP address and provides
  some other improvements. However, IPv6 is still
  not popular.

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Accessing Web Servers

• Domain name server (DNS)
• Maintains database of host names and
  corresponding IP addresses
• Translates fully qualified host name to IP
  address
• Known as DNS lookup

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HTTP

• Hypertext Transfer Protocol
• Developed around 1989 to 1990 by Tim Berners-Lee
  at CERN.
• A protocol for transferring hypertext documents
  over the Internet.
• Current version is HTTP 1.1
• Establish a TCP/IP connection from a client to
  remote host (port 80 by default).
• A request string is sent by the client
• The server responses by a response string
  containing the header as well as the body such as
  the file requested or an error message.
• The transmission is not secure.

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HTTP

• The standard for transferring hypertext documents
  (http//www.w3.org/Protocols/)
• Specifies HTTP requests and responses
• Example of a request
• GET /test/index.html HTTP/1.1
• Accept image/gif, image/x-xbitmap, image/jpeg,
  image/pjpeg, application/vnd.ms-excel,
  application/msword, /
• Accept-Language en
• Accept-Encoding gzip, deflate
• Connection Keep-Alive
• Host www.site.com
• User-Agent Mozilla/4.0

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HTTP

• Example of a response
• HTTP/1.0 200 OK
• Date Mon, 1 Mar 2004 153024 GMT
• Content-Type text/html charsetISO-8859-1
• (the actual content of the html follows)

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HTTP

• HTTP 1.1 supports persistent connections.
• Enables the client to send a request and get a
  response, and then send additional requests and
  get additional responses immediately.
• The TCP connection is not released for the
  multiple additional requests, so the overhead is
  less.

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HTTP Request Types

• Also known as request methods
• Most popular are GET and POST
• Retrieve and send client form data to Web server
• GET request
• Sends form content as part of URL
• e.g., http//www.google.com/search?hlenlrqint
  ernet
• The part after ? is the data being sent
• Retrieves appropriate resource from Web server
• Limits query to 1024 characters
• POST request
• Updates contents of Web server (posting new
  messages to forum)
• Has no limit for length of query
• Not part of URL and generally is not seen by user
• More discussion in Handout 2.

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Web Clients

• Web Clients
• Software that gives users access to the World
  Wide Web.
• Convert users requests to HTTP requests and
  communicate with Web servers.
• Web Spiders/Web Crawlers/Web Robots
• Software that automatically retrieves Web
  documents by standard HTTP protocol, either by
  following hypertext links or other methods.
• Web Browsers
• Web clients that provide a graphical interface
  that lets users click buttons, icons, and menu
  options to view and navigate Web pages.

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The First Web Browser (in early 1990s)

• Called WorldWideWeb (renamed Nexus later to avoid
  confusion)
• Developed by Tim Berners-Lee. It was also a HTML
  Editor

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Web Browsers

• Popular Web browsers/clients
• Internet Explorer (78.)
• Opera 7/8 (0.81)
• Mozilla/FireFox (16.36)
• Netscape (0.06)
• Safari (3.41)
• Have you used these?
• Mosaic (1992-1997)
• Lynx (a text-only browser/client)
• Safari and Camino/Chimera (Mac)
• Others?

Source of data http//en.wikipedia.org/wiki/Usag
e_share_of_web_browsers, 2008 Q2
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Web Browsers

• Browser War I (1995-1998)
• Microsoft IE vs Netscape Navigator/Communicator

• Netscape dominated the Web browser market in the
  mid-1990s.
• Microsoft wanted to gain the market bundled IE
  with Windows.
• And the rest is history.

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Web Browsers

• Browser War II (2004-2007)
• IE is often the target of Internet attack,
  including viruses, worms, adware and spyware.
• IE has poor compliance with many standards, such
  as CSS, PNG image format, and XHTML. See this
  page for examples http//www.positioniseverything
  .net/explorer.html
• IEs market share drops from around 85 in
  January 2004 to 70 in January 2005, mainly
  because of competition from FireFox.
• FireFox is built on Mozilla, the open-sourced
  version of Netscape Communicator after Netscape
  was purchased by AOL in 1997. FireFox is
  preferred by many techies.
• Browsers on PDA, phones, and other platforms?

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Web Browsers

• Browser War III ? (2008 - ?)
• IE 8
• Claims to have better security and privacy
  control
• Google Chrome
• Open source
• Faster Javascript
• FireFox 3
• Continue to improve
• More and more third-party add-ons