COMP 2121: Internet Technologies

1. COMP 2121:Internet Technologies Session 7: The Internet

2. Part 1: Accessing the Internet

3. Origin of TCP/IP • ARPAnet included 40 computers by 1972 • Architecture getting even more complex • Needed a reliable communications protocol suite

4. Origin of TCP/IP (2) • RFC proposal for TCP/IP accepted • Important features: IP addressing enables packet routing TCP guarantees packet receipt • TCP/IP became an International standard for digital messaging • Rubber stamped by OSI (Open Systems Interconnect)

5. DARPANET becomes “The Internet” • However, throughout the 1980s: only computer boffins understood TCP/IP and UNIX no-one else could use the Internet… • Main problem: TCP/IP – so complex • Software was needed that would enable text to be sent by non-specialists

6. Computer boffinfrom http://www.emdavis.com/babydavis/4_6months.htm

7. Accessibility • Protocols available to send graphics and other data across the Internet this would also be useful to non-specialists • It took a non-specialist to see this, and write the software • Enter Tim Berners-Lee…

8. Sirr Tim Berners-Leefrom http://www.radford.edu/srabago/links/text.html

9. Internet Browsers • Convert web pages into something visual that non-geeks can understand • Berners-Lee wrote browser software for two types of mainframe computer… • Other developers produced browsers to cover other Internet machines • Early browsers only displayed text and hyperlinks • unable to take advantage of graphics formats

10. Home Connections • In the UK, Demon Internet set up (1992) • Provided an Internet Connection service to any UNIX home user (£10 per month) • UNIX-based browser provided access to the World Wide Web • Unix not exactly a mass-market product…

11. Unix command windowfrom http://www.winsupersite.com/images/showcase/980926-4.gif

12. PCs without TCP/IP… • A PC without the TCP/IP protocol cannot use the Internet • In 1992, Windows 3.1 was the favoured PC operating system • Very much aimed at the “standalone computer”

13. And then with TCP/IP… (What a difference a year makes!) • It then all happened very quickly: • Some very clever people wrote the code that would make TCP/IP available as an alternative protocol for Windows 3.11 • Other clever people produced a browser for Windows 3.11 • Result: people all over the world discovered that their PCs could now access the World Wide Web

14. The problem • TCP/IP was not a standard feature of Windows 3.11 and needed installing and configuring • Not a job for the faint-hearted • Solution: Windows 95

15. The final piece in the jigsaw (Windows 95) • TCP/IP became a standard component • TCP/IP implementation (32-bit) was much more efficient than Windows 3.11 (16-bit) • Graphics and multi-media facilities were improved • Browsers could also be 32-bit, and provide a richer visual display • A link was available from the desktop to an Internet Service Provider

16. Why the Interest? • End-user costs surprisingly low considering the technology involved • subsidised by US government? • Competition kept Internet Service Providers prices down • Dial-up telephone charges could build up, however, even if charged at the local rate

17. Why so popular in the US/Canada? • In 1994-7, most Internet users were from North America • Reasons: • promoted by National governments • entrepreneurs were quick to see the potential of the new medium • local telephone calls were free…

18. Americanisation • Although physically an International medium, in this era, the Internet became widely regarded as “America On-Line” • Most content presented in [US] English • Why not UK? • Telephone costs expensive – no free local calls! • No government promotion • Media “nerdy” image

19. Nerdfrom http://www.infosun.fmi.uni-passau.de/st/misc/chaos.html

20. From http://www.chrismadden.co.uk/computer-cartoons/nerd-internet.gif

21. Why not Europe? • Most of Europe: • not English-speaking • less readily accessible • connection costs high • Biggest European growth in Scandinavia • high incidence of English-speaking • readily embrace new technology

22. Browsers (1) • Wide variety available • Internet Explorer (version 8.0, March 2009) • Windows only • Support for Mac versions discontinued • Mozilla Firefox (version 3.6, January 2010) • Multiple platforms, including Linux

23. Browsers (2) • Safari (version 4.0.5, March 2010) • Mainly used on Macs; Windows version available • Google Chrome (version 4.0.249.89, February 2010) • Windows, Mac and Linux • Opera (version 10.50, March 2010) • Mainly mobile devices • usage probably underestimated due to caching in proxies • And others…

24. Web Browser usage, February 2009from http://en.wikipedia.org/wiki/File:Web_browser_usage_share.svg

25. Web Browser usage, February 2010from http://en.wikipedia.org/wiki/File:Web_browser_usage_share.svg

26. Browser usage (February 2010)from http://en.wikipedia.org/wiki/Comparison_of_web_browsers

27. Rendering (Layout) Engines • The software that controls the display of markup (including html) on the screen • The browser simply adds toolbars, etc. • Limited number of rendering engines: • Gecko (Firefox) • Trident (Microsoft IE) • Presto (Opera) • WebKit (Safari, Chrome) • and a few others

28. The Microsoft Controversy • Microsoft bundles IE with Windows • Considered anti-competitive • Result: ballot window in newest versions of Windows • Allows user to select browser • But not all browsers immediately visible – many require scrolling • And most of those on the first page seem to use the Trident rendering engine…

29. Part 2: Internet Organisation

30. W3C • World Wide Web Consortium • Produces recommendations for standards • Which may or may not be adopted by manufacturers • Handles the technical side of the Internet

31. ICANN • Internet Corporation for Assigned Names and Numbers • Born out of ARPANET • But now nominally independent of the US government • IP address allocation • Domain names (esp. top-level domains) • UDRP (Uniform Domain Name Dispute Resolution Policy) • Handles disputes over ownership of domain names • Cybersquatting

32. IANA • Internet Assigned Numbers Authority • Actually does the work of IANA for IP address and most top-level domain name allocation • Including country-level domain names • But .com and .net delegated to Verisign • Lower-level domain name allocation delegated to RIRs

33. RIRs • Five in all: • RIPE (Europe, Middle East, central Asia) • ARIN (N. America) • APNIC (Asia & Pacific) • LACNIC (Latin American & Caribbean) • AfriNIC (Africa) • Handle delegated regional allocation of IP addresses and domain names

34. RIRs Areas of Influencefrom http://en.wikipedia.org/wiki/File:Regional_Internet_Registries_world_map.svg

35. ISPs • Provide Internet access to customers • Using resources granted by an RIR • To individuals • To organisations of all sizes • (larger organisations my go direct to a RIR)

36. Services provided by ISPs • Internet access • Browsing • E-mail • Hosting • Most charge • Some do not, but expect users to put up with advertising

37. Part 3: Web sites

38. What is a Web Site? • Collection of html files for web pages stored on a server • Downloaded on request to a client using http • Displayed by a browser on the client machine

39. www Servers • The computer providing the www service: • should be registered as a domain name • can be configured to host one or many websites • keeps each site in a separate folder

40. UNC names • Universal (or Uniform) Naming Convention • Devised specifically to identify device and service names on a domain-based Windows NT/2000 network • Note the “DOS-based” \ (back slash) • as opposed to the “Unix-based / (forward slash) • Server prefixed by \\ • e.g. \\applications • Shares, devices or services prefixed by \ • e.g. \\main\admin\student_data.html

41. Arrangement of files on server (1) • Flat field: all files within one folder • Advantages: • simple structure • simple paths to files • Disadvantages: • Cumbersome for large sites with many pages • Difficult to find files for updating • No structure to page urls for users • Secondary files (e.g. images, CSS, templates) mixed in with page files

42. Arrangement of files on server (2) • Hierarchical • Structure using folders • Each folder holds files related to one another • a sub-site • Folders may contain other folders…

43. Hierarchical structure • All files on a particular topic are together • Easily changed, extracted… • Possible to have several files with the same name but in different folders • e.g. links.html • Secondary files, e.g. images, can be grouped together • (Minor) disadvantage: planning needed

44. Databases • Structured for easy querying • And easy updating • Relationships between tables should enable this easily • For web based databases as well as ‘ordinary’ ones • At least ‘third normal form’ • And possibly sixth normal form

45. Static and dynamic web pages • Static pages appear the same every time • To every client machine, to every user, in every place, at every time of day… • Minor differences due to browser quirks… • Dynamic pages appear different • For different users • At different times • In different locations…

46. NPARU viewed with IE7the word ‘Date’ is below the background cloud…

47. NPARU viewed with Firefox

48. Advantages of dynamic pages • Can be related to the user’s needs • Can be used for targetted advertising • Aimed at individuals • In particular places • At particular times • (but see the current concern over Phorm) • Can be dependent on user input • Content of a form field

49. Dynamic web pages • Client scripts • Run on the client machine • Use information available on the client machine • Server scripts • Run on the server • Output transmitted to the client and displayed there • Able to make use of information available to the server, but not to the client • e.g. large database

50. Web Design: Future proofing • Use the latest recommended version of markup language • Keep pages up to date with changes in W3C recommendations • Pages will then be viewable on most platforms • And those that can’t view your pages will be at fault, not you