THE INTERNET AND INTRANETS

1
CHAPTER 4

• THE INTERNETAND INTRANETS

2
What is the Internet?

• A collection of interconnected networks, all
  freely exchanging information
• The Largest computer network in the world (a
  network of networks)
• Exchanges information seamlessly by using the
  same open, non-proprietary standards and
  protocols, within interconnected networks
• Forms a massive electronic communications network

3
The Evolution of the Internet
4
The Infrastructure of the Internet

• Commercial communications carriers provide the
  physical network backbone of the Internet
• Internet Service Providers
• Backbone providers
• Access providers
• Reciprocal agreement

5
The Operation of the Internet

• Internet is packet-switched network
• Client-Server architecture
• Internet Protocol
• Internet Model

6
Internet Model

• Interface layer defines physical medium and frame
  for flow and error control
• Internet network layer defines the path to
  intended receiver in the network. Uses Internet
  Protocol (IP)
• Internet transport layer provides point-to-point
  reliable transmission of data. Uses TCP and UDP.
• Internet application layer supports network
  application

7
OSI Model vs. Internet Model
8
Internet Application Layer

• File Transfer Protocol
• Telnet
• Simple Mail Transfer Protocol
• Simple Network Management Protocol
• HyperText Transfer Protocol
• Domain Name System

9
Addresses on the Internet

• IP address uniquely identifies each computer in
  the network
• Example 130.63.160.120
• The necessity to keep a master table with IP
  addresses on each router
• Hard to remember for people
• Uniform Resource Locator
• Domain name system (DNS) - derives the names of
  the computers

10
Domain name system (DNS)

• Domain a group of networks
• Domains are organized hierarchically
• DNS is based on hierarchical database
• Variable-depth hierarchy
• Distributed database
• Exampleswww.atkinson.yorku.ca
• www.yorku.ca

11
Accessing the Internet

• Connect via LAN Server
• Communications stack
• Connect via Serial Line Internet
  Protocol/Point-to-point Protocol (SLIP/PPP)
• Connect via an Online Service

12
Internet Services

• Communications services
• Information retrieval services
• World Wide Web

13
Communications Services Provided by the Internet

• E-mail
• Instant messaging
• Internet telephony
• Voice-over-IP
• Video conferencing
• Content streaming

14
The World Wide Web

• The Internet functions as the transport mechanism
  
• The World Wide Web - a system with universally
  accepted standards for storing, retrieving,
  formatting, and displaying information
• Web Servers support WWW application, are
  scattered all over the world

15
Web site

• Web Site
• Home Page - first, introductory page in a web
  site
• Webmaster - the person in charge of a Web site
• Uniform Resource Locator (URL)

16
Browser

• software application that is used to access and
  navigate the Web
• Netscape Communicator
• a multipurpose suite that handles news, e-mail,
  audio- and video conferencing, and more
• Microsoft Internet Explorer
• Internet Explorers tight integration with
  Windows offers users the advantage of one-stop
  computing

17
Search Engines

• Programs that return a list of Web sites or pages
  that match some user-selected criteria
• Ways to select pages for inclusion in the
  database
• Web Crawlers
• TITLE HTML element
• Registration sponsored link

18
Web Authoring

• Standard HTML is the common denominator
• Enhancements to HTML
• Dynamic HTML (DHTML) (slide 6, Introduction to
  HTML)
• Extensible markup language (XML)
• Voice markup language (VoxML)
• Virtual reality modeling language (VRML)
• HTML editors, generators, publishers
• Java

19
Internet Privacy

• Web sites collect information about visitors
• Registration
• Clickstream data
• Cookie is a mechanism that supports restoring
  client states
• small data file placed on users hard drives
  when they first visit a site

20
Internet Security

• Encryption the process of converting a message
  into a secrete code
• Plain text original message
• Ciphertext encrypted text
• Decryption - the process of converting an
  encrypted message into regular text
• Digital signature is used to verify the identity
  of a message sender

21
Intranets

• A private network that uses Internet software and
  TCP/IP protocols
• Process business data and information
  efficiently
• Data and information search
• Urgent information delivery
• Information distribution

22
Intranet operation

• Intranet documents HTML pages
• HTTP used to transmit documents
• Browsers allow to view Intranet documents
• Intranet vs. traditional networks
• HTTP and HTML platform independent
• A single input point a browser

23
Extranet

• A network that links business partners to one
  another over the Internet by providing access to
  certain areas of each others corporate intranets
• Extranet infrastructure
• Virtual private network
• Firewall

24
Virtual Private Network

• A secure connection between two points across the
  Internet
• Provides the means for conducting private
  communications over the public Internet.
• VPN vs. privately owned network

25
Tunneling

• The process by which VPN transfers information
• Messages include data along with private protocol
  information
• Does not substitute encryption

26
Firewalls

• A system designed to prevent unauthorized access
  to or from a private network.
• Firewalls can be implemented in
• Hardware
• Software
• a combination of both.