1 / 63

COMP 2121: Internet Technologies

COMP 2121: Internet Technologies. Session 7: The Internet. Part 1: Accessing the Internet. Origin of TCP/IP. ARPAnet included 40 computers by 1972 Architecture getting even more complex Needed a reliable communications protocol suite. Origin of TCP/IP (2). RFC proposal for TCP/IP accepted

hateya
Télécharger la présentation

COMP 2121: Internet Technologies

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related