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2. Some history How the Internet works How the World Wide Web works Protocols The Internet and the Web

3. 3 First you had computers  Stand-alone – originally big, flashing lights, wiring, men in white coats and pocket protectors, air-conditioned mainframes  Then mini-computers  Then PCs

4. 4 Then you had networks of computers Each of these networks connected in its own ways – different communication systems.

5. 5 Then you had networks of networks They are connected to each other, somehow or other 'internetworks'

6. 6 You’ve got … Physical Networks  LAN 'local area networks'– could be a building or more  MAN 'metropolitan area networks' (Kentish MAN) Logical Networks  Within a business or a university or... –Intranets And you’ve got the Internet And you’ve got wireless networks

7. Some history How the Internet works How the World Wide Web works Protocols The Internet and the Web

8. 8 What is the Internet  It’s a network of networks, a global super- network – and it’s not just any such – Overall, it works in a specific kind of way and it is really global.  As we know it, it was invented 30 years ago and deployed 20 years ago.

9. 9 The Internet before the Web  Email – STMP (Simple Mail Transfer Protocol) (actually predates the internet)  Usenet (bulletin boards)  Gopher (something like a search engine) ...

10. 10 IP addresses (Internet protocol)  All networked computers have IP addresses 129.12.185.83 The IP address of the computer I was using when I originally made this slide IP = “Internet Protocol”

11. 11 Computers connected to the Internet (and other networks) are given IP addresses

12. 12 IP addresses  A unique number that refers to a device on a network  What have IP addresses? Web-sites, servers, your pc, the printer in the hallway... (some are static – they stay the same, some are dynamic,...)  IP addresses are used over LANs as well as over the Internet

13. 13 IP addresses  www.cs.kent.ac.uk resolves to 129.12.4.58 www.cs.kent.ac.uk  www.kent.ac.uk resolves to 129.12.200.17 www.kent.ac.uk  www.gre.ac.uk resolves to 193.60.49.86 www.gre.ac.uk  www.whitehouse.gov resolves to... 84.53.134.9 and 84.53.134.14 [among others] www.whitehouse.gov

14. 14 What almost happens going across the Internet

15. 15 The Internet A model representing roughly how it works: Not the Telephone service the Postal service! The technical term is “packet switching”. Imagine you wanted to send an encyclopaedia to someone by post, but you could only put a sheet or two of paper in an envelope. You’d need to ‘tear’ the encyclopaedia up in a reasonable way, note down the order that the sheets needed to be in and send a sheet or two in each envelope. The at the other end everything would need to be put together again. An even better analogy – POSTCARDS.

16. 16 The TCP/IP Postcard analogy From Pearson Education, Inc.

17. 17 What the Internet isn’t  It is NOT like the telephone service – In the telephone service there’s a single dedicated connection all across the network(s) between the two ends of the conversation. This uses a lot of network resources. Although it makes use often of telephone technology  On the Internet, there’s no connection from one end to the other and parts of what’s crossing the Internet may have followed different routes

18. 18 Various routes may be used

19. 19 Types of networks  Circuit switching – like the original telephone networks  Packet switching – like the internet  Broadcast – like radio, television and the Ethernet

20. 20 The TCP/IP TCP/IP – Transmission Control Protocol over IP Using TCP, computers can exchange messages (data) in packets across an inter-network, with the assurance that these packets can be delivered reliably, in- order (if something has gone wrong, likely to know about it) with flow control

21. Some history How the Internet works How the World Wide Web works Protocols The Internet and the Web

22. 22 History goes on... In the late 80s & early 90s, the Internet just academia & large corporations. used only for e-mail, newsgroups... There was also Hypertext, but it was limited to applications where one could use the links to move around a single complex set of documents on a single machine. Then along came Tim Berners-Lee – he put these together with some other inventions - and he invented the World Wide Web.

23. 23 What got the www going  The first Web server  A combination browser and editor  http  URL  HTML  Running on the Internet  Lots and lots of different people and organisations throughout the world Invented by Tim Berners-Lee

24. 24 What the WWW runs on:  Web servers  Browsers  HTML  http  URLs  The Internet Tim Berners-Lee

25. 25 So, what is the www?  “An internet-based hypermedia initiative for global sharing” http://www.w3.org/People/Berners-Lee/Overview.html

26. 26 What users see: Domain names  www.yahoo.com  www.cs.kent.ac.uk  www.kent.ac.uk  en.wikipedia.org  ftp.internic.net  Are easy to use  Are easy to remember  May reflect something about the organisation  Are not as easily handled by machines as numbers are

27. 27 Domain hierarchy.uk.ac.kent.cs

28. 28 Top-Level Domains (TLDs) Generic Top-Level Domains .com .org .net .edu .int .mil Country Code Top Level Domains .uk .fr .de .us .jp .au .ca

29. 29 URLs (Universal Resource Locator) http://en.wikipedia.org/wiki/URL host 'path' 'scheme'

30. 30 URLs (Universal Resource Locator) http://en.wikipedia.org/wiki/URL server Path on the server What to use subdomain Top level domain

31. 31 Domain name system (DNS)  Connects Domain names with IP addresses 129.12.185.83

32. 32 http “HyperText Transfer Protocol” HyperText – ? Transfer – ? Protocol - ?

33. Some history How the Internet works The World Wide Web works Protocols The Internet and the Web

34. 34 Protocols  Communication protocols specify how computers can talk to each other.  Networks need agreed upon conventions of how to communicate. Protocols set down these procedures, often by specifying the format of a message and how errors are to be handled.

35. 35 http again  It sets down how two computers (‘client’ ‘server’) can have a ‘conversation’  General Pattern – request / response request: “I’d like you to give me X” response: “Here” – sending X

36. 36 Layers Many different protocols may be involved in a complex communication across a network.  HTTP hypertext transfer protocol (application layer)  TCP transmission control protocol (transport layer)  IP internet protocol (network layer)  PPP - point-to-point protocol (data-link layer)

37. 37 W3C The World Wide Web Consortium (W3C) are one the key groups who set Web standards. You'll be learning about HTML this week. We’ll also be talking about some specific examples of HTML (HTML 4.01 for example) It’s the people at W3C who set out the rules that govern whether or not something fits the standard

38. 38 On your own  To find the IP address of a computer in Windows XP or Vista (?), open a Command Prompt and enter ipconfig.exe  You can watch network traffic in the neighbourhood of a public PC by using Wireshark (Open from the start menu >> computer science then capture > start.)

39. From 2009 exam paper: Networks, the Internet & the web (i) What is packet switching? What is circuit switching? What is broadcast? For each of these three, name one system that uses this method. [3 marks] (ii) The URL for the University of Kent student portal is https://portal.kent.ac.uk/uPortal What does http mean? What does the ‘s’ in https indicate? In the context of this URL, what does ‘portal’ refer to? What does /uPortal refer to? [2 marks]

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