computing revision

computing revision

1. what is a network

   • A network is a series of computers and other devices that are connected together and can share data and resources The biggest network in the world is the Internet, a collection of networks all round the world No one person or organisation owns the Internet

2. The Internet and the World Wide Web

   • The Internet is an International Network of computers – a network of networks The World Wide Web is one use we get from that network

3. What is a Wide Area Network

   • Any network in which the computers communicate using resources supplied by a “third party carrier” such as British Telecom, is a Wide Area Network Often under collective or distributed ownership A WAN uses cables, telephone lines, satellites and radio waves to connect, usually spread over a wide geographical area

4. A circuit switching network

   • When you make a telephone call, a dedicated connection is set up between you and the person you are calling for the duration of the call This is called “circuit switching”

5. Domain Name System (DNS)

   • DNS technology allows you to type a name such as google.co.uk into your web browser It translates the web address google.co.uk into an IP address e.g. www.google.co.uk = 74.125.131.94 What happens when you type an IP address into a browser?

6. Data packets

   • Each data packet will contain the same number of bytes Each packet is marked with the packet number and the total number of packets in the transmission

7. Passing packets across the net

   • Each node is a crossroads and requires something to direct data packets to their destination along the path which is least busy at that moment This is the job of a router

8. DNS servers

   • There are 13 DNS “root” servers worldwide which keep a complete database of all names and IP addresses Other DNS servers lower down the hierarchy hold parts of the database When a DNS server receives a request not in its database, it will pass the request on to another server until it reaches one with the matching name and IP address

9. IP addressing

   • Every computer and other device connected to the Internet has an IP address EPackets are labelled with the sender’s and the destination IP addresses Packets are sent across the Internet separately via different routes and reassembled at the end .g. 81.101.137.12

10. IPv4 Addressing

    • 72.129.214.16 There are now so many computers that the number of available IPv4 addresses is running out A new IPv6 system of addressing is replacing IPv4 This is largely owing to the ‘Internet of Things’