5. Language
For our purposes, a language is an agreed way to structure some
information.
Computers use lots of languages but the only one we care about today
is
• Hypertext Markup Language (HTML)
Other languages relevant to the Web include; CSS, PHP, JavaScript,
XML. But that’s too much for this talk!
6. Protocol
A protocol is how two parties communicate. For our purposes, it’s two
computers talking to each other.
Today we’ll briefly cover:
• Internet Protocol
• Transmission Control Protocol
• Domain Name System
• Hypertext Transfer Protocol
8. Bonjour
Merci, revenez nous voir
Je vous remercie
Voici votre pomme et 4,44 € de monnaie
Voici 5 €
Ce sera certainement 0,56 €
Bonjour
Je voudrais acheter cette pomme
11. Internet Protocol (version 4)
Internet Protocol (IP) Addresses are just a big number to identify each
device on the Internet.
Version 4 addresses are usually written as four numbers, each from 0-
255 with dots between them.
152.78.71.1
4,294,967,296 addresses. Not enough for one per person.
13. Internet Protocol (version 6)
Version 6 addresses are usually written as numbers and the letters A-F
with colons between the bits.
2001:db8:0:1234:0:567:8:1
340,300,000,000,000,000,000,000,000,000,000,000 addresses.
Should keep us going a while.
15. At each step of it’s journey a computer looks at the address on the packet
and sends it to a connected comuter nearer the destination.
Like a real world sorting office.
• My laptop
• Wifi hub
• Imperial Router
• Imperial Firewall
• JaNET
• Soton Firewall
• Soton Router
• My server at Southampton
Packets do get lost sometimes. Or stuck in loops!
22. Transfer Control Protocol
Establishes two computers communicating with each other.
We start by sending a few postcards (packets) each way to agree to set
up the “TCP/IP connection”.
Then we start numbering each message to ensure the correct order.
30. The whole page you just asked for described in the
Hypertext Markup Language
It’s in HTML
200 OK
Could I have /events/grad.html from www.meh.ac.uk, please?
http://www.meh.ac.uk/events/grad.html
1. Use the Domain Name Service to find out the Internet Protocol address of
www.meh.ac.uk
2. Establish a Transfer Control Protocol connection to that Internet Protocol address
3. Use that connection to ask for the page we want:
34. HTML
<p>Everything inside a “p” element is a single
paragraph.</p>
<a href=“http://totl.net/”>This is a link to the
URL in the href attribute.</a>
<p>This is an example of a paragraph with <a
href=“https://vfringe.co.uk/”>one</a> or <a
href=“https://www.boomtownfair.co.uk/”>two</a>
links within it.</p>
35. <p>This is an example of a paragraph with <a
href=“https://vfringe.co.uk/”>one</a> or <a
href=“https://www.boomtownfair.co.uk/”>two</a>
links within it.</p>
p
“This is an example of a paragraph with “
a - linking to https://vfringe.co.uk/
“one”
“ or “
a - linking to https://www.boomtownfair.co.uk/
”two“
“ links within it.”