CHAPTER 4

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 Marina G. Erechtchoukova

3. The Evolution of the Internet Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

5. The Operation of the Internet • Internet is packet-switched network • Client-Server architecture • Internet Protocol • Internet Model Marina G. Erechtchoukova

6. Internet Model • Interface layerdefines 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 Marina G. Erechtchoukova

7. OSI Model vs. Internet Model Marina G. Erechtchoukova

8. Internet Application Layer • File Transfer Protocol • Telnet • Simple Mail Transfer Protocol • Simple Network Management Protocol • HyperText Transfer Protocol • Domain Name System Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

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 • Examples:www.atkinson.yorku.ca www.yorku.ca Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

12. Internet Services • Communications services • Information retrieval services • World Wide Web Marina G. Erechtchoukova

13. Communications Services Provided by the Internet • E-mail • Instant messaging • Internet telephony: • Voice-over-IP • Video conferencing • Content streaming Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

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) Marina G. Erechtchoukova

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 Explorer’s tight integration with Windows offers users the advantage of “one-stop computing” Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

22. Intranet operation • Intranet documents – HTML pages • HTTP – used to transmit documents • Browsers – allow to view Intranet documents • Intranet vs. traditionalnetworks: • HTTP and HTML platform independent • A single input point – a browser Marina G. Erechtchoukova

23. Extranet • A network that links business partners to one another over the Internet by providing access to certain areas of each other’s corporate intranets • Extranet infrastructure: • Virtual private network • Firewall Marina G. Erechtchoukova

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 Marina G. Erechtchoukova

25. Tunneling • The process by which VPN transfers information • Messages include data along with private protocol information • Does not substitute encryption Marina G. Erechtchoukova

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. Marina G. Erechtchoukova