Transcript Slide 1

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The Internet and the Web
Some history
How the Internet works
How the World Wide Web works
Protocols
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
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Then you had networks of
computers
.
Each of these networks
connected in its own ways
– different communication
systems
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Then you had
networks of networks
'internetworks'
They are connected to each
other, somehow or other
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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
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The Internet and the Web
Some history
How the Internet works
How the World Wide Web works
Protocols
What is the Internet
 It’s a network of networks, a global supernetwork – 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.
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The Internet before the Web
 Email – STMP (Simple Mail Transfer
Protocol)
(actually predates the internet)
 Usenet (bulletin boards)
 Gopher (something like a search engine)
 ...
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IP addresses (Internet protocol)
 All networked computers have IP
addresses
129.12.185.83
IP = “Internet Protocol”
The IP address of the computer I was using when I originally made this slide
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Computers connected to the Internet
(and other networks) are given IP
addresses
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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
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IP addresses
 www.cs.kent.ac.uk
resolves to 129.12.4.58
 www.kent.ac.uk
resolves to 129.12.200.17
 www.gre.ac.uk
resolves to 193.60.49.86
 www.whitehouse.gov
resolves to ... 84.53.134.9 and 84.53.134.14
[among others]
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What almost happens going
across the Internet
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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.
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The TCP/IP Postcard analogy
From Pearson Education, Inc.
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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
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Various routes may be used
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Types of networks
 Circuit switching – like the original
telephone networks
 Packet switching – like the internet
 Broadcast – like radio, television and the
Ethernet
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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, inorder (if something has gone wrong, likely
to know about it) with flow control
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The Internet and the Web
Some history
How the Internet works
How the World Wide Web
works
Protocols
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.
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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
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What the WWW runs on:






Web servers
Browsers
HTML
http
URLs
The Internet
Tim Berners-Lee
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So, what is the www?
 “An internet-based hypermedia initiative
for global sharing”
http://www.w3.org/People/Berners-Lee/Overview.html
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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
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Domain hierarchy
.uk
.ac
.cs
.kent
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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
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URLs (Universal Resource Locator)
http://en.wikipedia.org/wiki/URL
host
'path'
'scheme'
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URLs (Universal Resource Locator)
http://en.wikipedia.org/wiki/URL
server
subdomain
What to
use
Path on
the
server
Top level
domain
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Domain name system (DNS)
 Connects Domain names with IP
addresses
129.12.185.83
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http
“HyperText Transfer Protocol”
HyperText – ?
Transfer – ?
Protocol - ?
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The Internet and the Web
Some history
How the Internet works
The World Wide Web works
Protocols
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.
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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
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Layers
Many different protocols may be involved in
a complex communication across a
network.
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
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HTTP hypertext transfer protocol
TCP transmission control protocol
IP internet protocol
PPP - point-to-point protocol
(application layer)
(transport layer)
(network layer)
(data-link layer)
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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
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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.)
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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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