How the WWW & the Internet Work or "I didn't know they aren't the same thing."

1. How the WWW & the Internet Work or "I didn't know they aren't the same thing." Instructor: Joseph DiVerdi, Ph.D.

2. How the Internet Works • The Internet is a communications medium through which information is transferred between computers • Many different services use the Internet for transferring information • They most often use TCP/IP to transfer data • Transmission Control protocol/Internet Protocol • The telephone network is also a communications medium but with very different characteristics

3. How the WWW Works • The World Wide Web is an information service that uses the Internet as its communication medium • It is based on the technology called hypertext • Hypertext is a method of presenting information • Selected words in a text can be "expanded" • to provide other information about the word • These words are called links to other documents, e.g., text, files, pictures, etc.

4. How the Internet Works • The Internet is a packet switched network • When data leaves the source computer it is broken up into packets (small chunks of data) and transmitted through larger and larger networks (usually 1-1,500 bytes long) • The packets are routed through the many networks • When the packets arrive at the destination computer they are reassembled into the original message

5. How the Internet Works • Breaking the data up into small packets increases the efficiency of the whole network • The exact path taken from the same source to the same destination is often different • The path depends on the instantaneous load on each of the routers and networks • The packet data is identified by the Internet Addresses of the source and destination computers

6. Network Analogies • The telephone network is a circuit switched network • When a telephone call is made a piece of the network is dedicated to that call • Even if it isn't being used, e.g., being on hold, that piece of the network is unavailable for use by others • Inefficient utilization of Network Resources

7. Network Analogies • The US postal Service is a packet switched network • No user receives a dedicated piece of the network • Routers are equivalent to Postal substations • Mail sent from Milford, CT to Loveland, CO does not use a reserved plane or truck - it is pooled at a substation and sent to a series of substations • Efficient utilization of Network Resources

8. Internet Addresses • An IP address uniquely identifies a computer • IP addresses follow dotted decimal notation • Four decimal numbers • Each ranging from 0 to 255 • Each number separated by a period • The following are unique IP addresses and corresponding to unique computers: • 206.168.235.2 • 192.122.36.5 • 128.174.5.6 • IP addresses are registered and allocated

9. Domain Name System • A Host Name is assigned to each computer only for the convenience of human users • Computers are quite happy to refer to each other by IP addresses • Host Names use a hierarchical Domain structure • right-to-left <--> most-to-least significant • Each domain is separated by a period • Host Names are registered and allocated

10. Host & Domain Names • The following are unique host names corresponding to unique computers: • woody.xtrsystems.com • lamar.colostate.edu • holly.colostate.edu • nic.ddn.mil • whitehouse.gov • uxc.cso.uiuc.edu • ux1.cso.uiuc.edu • One computer may have several host names

11. Original High-level Domains Domain Usage com Commercial organizations edu Educational organizations gov Non-military government organizations mil Military organizations org Other organizations net Network resources

12. Country Domains • The Internet is a world-wide network • Foreign (relative to the USA) countries have responsibility for their own names • Country codes are a set of two letter highest-level country domains • About 300 country codes exist BO - Bolivia BR - Brazil IR - Iran CA - Canada TD - Chad IQ - Iraq FR - France DE - Germany UK - UK US - USA TO - Tonga TW - Taiwan

13. Domain Name Lookup • Convert a Domain Name into an IP address • Use DNS servers • computers whose sole purpose is to maintain lists of IP addresses and domain names • Local DNS servers know local addresses • DNS servers also cache recently requested addresses • Local DNS servers also know addresses of more-significant-domain name servers

14. How Intranets Work • An intranet is a private network • It uses the same components as the Internet • It is unconnected to the Internet • It is limited by physical boundaries • It is for the sole use of certain members • Those members exist within those boundaries

15. How Extranets Work • An extranet is a private network • It uses the same components as the Internet • Its members are connected through the Internet • It is not limited by physical boundaries • It is limited by logical boundaries • special (secret) protocols or encryption • It is for the sole use of certain members • Those members exist anywhere

16. Country Domains • The following are unique host names corresponding to unique computers: • hockey.guelph.ca • alpha.psd.k12.co.us • ci.fort-collins.co.us • uxc.urbana.il.us • Host Names are registered and allocated

17. non-WWW Internet Services • Other services which use the Internet as a communications medium • Nothing to do with the WWW • Telnet provides Login to remote computers • FTP provides inter-computer File Transfer • email provides jokes for everyone • Newsgroups provide Bulletin Boards • Internet Relay Chat (IRC) provides chat rooms

18. Telephone Services • Voice transmission • Fax Transmission

19. A Very Simple Transaction

20. Simple Transaction w/ Image