1

Some historyHow the Internet worksHow the World Wide Web worksProtocols

The Internet and the Web

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

Then you had networks of computers

Each of these networks connected in its own ways – different communication

systems

.

5

Then you hadnetworks of networks

They are connected to each other, somehow or other

'internetworks'

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 ...

– IntranetsAnd you’ve got the InternetAnd you’ve got wireless networks

Some history

How the Internet worksHow the World Wide Web worksProtocols

The Internet and the Web

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

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

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The IP address of the computer I was using when I originally made this slide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

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

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

IP addresses

www.cs.kent.ac.ukresolves to 129.12.4.58

www.kent.ac.ukresolves to 129.12.200.17

www.gre.ac.ukresolves to 193.60.49.86

www.whitehouse.govresolves to ... 84.53.134.9 and 84.53.134.14 [among others]

14

What almost happens going across the Internet

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

The TCP/IP Postcard analogy

From Pearson Education, Inc.

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

Various routes may be used

19

Types of networks

Circuit switching – like the original telephone networks

Packet switching – like the internet Broadcast – like radio, television and the

Ethernet

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

Some historyHow the Internet works

How the World Wide Web works

Protocols

The Internet and the Web

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

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

What the WWW runs on:

Web servers Browsers HTML http URLs The Internet

Tim Berners-Lee

25

So, what is the www?

“An internet-based hypermedia initiative for global sharing” http://www.w3.org/People/Berners-Lee/Overview.html

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

Domain hierarchy

.uk.ac

.kent.cs

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

URLs (Universal Resource Locator)

http://en.wikipedia.org/wiki/URL

host 'path'

'scheme'

30

URLs (Universal Resource Locator)

http://en.wikipedia.org/wiki/URL

server Path on the

serverWhat to use

subdomain

Top level domain

31

Domain name system (DNS)

Connects Domain names with IP addresses

129.12.185.83

32

http

“HyperText Transfer Protocol”HyperText – ?

Transfer – ?

Protocol - ?

Some historyHow the Internet worksThe World Wide Web works

Protocols

The Internet and the Web

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

http again

It sets down how two computers (‘client’ ‘server’) can have a ‘conversation’

General Pattern – request / responserequest: “I’d like you to give me X”response:

“Here” – sending X

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

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

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.)

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 ishttps://portal.kent.ac.uk/uPortalWhat 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]

40