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Some historyHow the Internet worksHow the World Wide Web worksProtocols
The Internet and the Web
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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 hadnetworks of networks
They are connected to each other, somehow or other
'internetworks'
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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 ...
– 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
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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.
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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
The IP address of the computer I was using when I originally made this slide
IP = “Internet Protocol”
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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.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]
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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, 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
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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
.kent.cs
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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 Path on the
serverWhat to use
subdomain
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 - ?
Some historyHow the Internet worksThe World Wide Web works
Protocols
The Internet and the Web
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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 / responserequest: “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.
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)
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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.)
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]
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