1. OCR GCSE Computing © Hodder Education 2013 Slide 1
Chapter 6: Internet
OCR GCSE Computing © Hodder Education Slide 1

2. OCR GCSE Computing © Hodder Education 2013 Slide 2
Chapter 6: Internet
The internet is:
A worldwide network of networks.
Linked by a common set of protocols (TCP/IP).
Used by billions.
Supports many applications such as
the world wide web;
instant messaging;
file transfer; .
Reliable because of redundancy.
Many alternative routes available from A to B.
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3. OCR GCSE Computing © Hodder Education 2013 Slide 3
Chapter 6: Internet
Digital and analogue
Computers use digital signals.
Many internet connections are via the Plain Old Telephone System (POTS).
Many telephone systems use analogue signals.
This requires a modem (modulator / demodulator) to do the conversion.
This is not needed if a digital link is used.
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4. OCR GCSE Computing © Hodder Education 2013 Slide 4
Chapter 6: Internet
Bandwidth is the difference between the upper and lower frequencies in a set of carrier signals.
it is often taken to mean the rate of data transmission in a network.
Broadband means a channel carries many frequencies.
This means that it has bigger data carrying capacity than narrow band.
>4Mbit/sec is considered to be broadband
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5. OCR GCSE Computing © Hodder Education 2013 Slide 5
Chapter 6: Internet
ADSL
asymmetric digital subscriber line;
uses spare capacity on POTS;
more bandwidth in the down direction than in the up direction;
most users download more than they send.
Cable
Subscribers to cable TV can access the internet via a cable modem.
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6. OCR GCSE Computing © Hodder Education 2013 Slide 6
Chapter 6: Internet
Router
A router is a device that connects networks.
It selectively passes data between networks.
They are at the heart of the internet.
They guide data packets to their destination.
ADSL modems often have router functionality built in for home networking.
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7. OCR GCSE Computing © Hodder Education 2013 Slide 7
Chapter 6: Internet
IP addressing
Every node on the internet has an IP (internet protocol) address.
Just like any network, an IPv4 address it is made from four 8- bit numbers, e.g
Private networks have their own IP addresses.
The router that connects a network to the internet has an IP address.
DNS servers change domain names, such as OCR.org.uk, to IP addresses.
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8. OCR GCSE Computing © Hodder Education 2013 Slide 8
Chapter 6: Internet
HTML is Hypertext Markup Language.
A way of adding tags to text.
Tells browsers how to display text.
Incorporates many extra features to allow tables, links, images and applications to be embedded in a web page.
Supports scripting languages such as JavaScript.
XML (Extensible Markup Language) is an open standard for encoding documents which supports Unicode.
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9. OCR GCSE Computing © Hodder Education 2013 Slide 9
Chapter 6: Internet
Standards
Many standards have evolved to make files interchangeable on the internet.
Standard
Use
JPG
Compressed images
GIF
Compressed small images
PDF
Documents
MP3
Music
MPG
Movies
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10. OCR GCSE Computing © Hodder Education 2013 Slide 10
Chapter 6: Internet
Compression
Many files take too long to download because they are too big, e.g. pictures, movies and music.
They have to be compressed in order to reduce download times.
Lossy compression
This reduces file size by removing data.
The data cannot be recovered later.
The data removed is chosen to have minimal effect.
Lossless compression
This keeps all the data.
It allows reconstruction of the original file.
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11. OCR GCSE Computing © Hodder Education 2013 Slide 11
Chapter 6: Internet
Compression
Lossy compression
An image of Coney island
The original is 1.3MB and it has been compressed to 324KB
OCR GCSE Computing © Hodder Education Slide 11