NETWORKS

NETWORKS

1. A network is a group of computers connected together so they can communicate

2. Networks allow computers to: Share files, so the same files are available whichever computer you use Share resources such as printers and Internet connection. Share Logins, so the same username and password can be used on every computer on the network.

   • INTERNET
     • The Internet is a world-wide network Devices on the Internet need IP Addresses, just like any other network
     • The Internet is a huge, global inter-connected network of devices. When we join the Internet, we use a broadband router to connect to one of the existing nodes.
     • Rather than using a star, bus or ring topology, each node is connected to one or more other nodes in an ad-hoc manner The layout of these nodes is called a Mesh Topology In a mesh topology, there is excellent resilience to outages as messages can take many different routes to reach a destination If any node or connection becomes unavailable, the message can simply take a different route
     • All data on the Internet is split up into small chunks called packets Each packet is numbered and sent independently This means that each packet may end up taking a completely different route through the mesh The packets are re-assembled on the other side
     • Before we can transmit, we need to decide what route the data is going to take In order to do this, each node continually tests its connections and assigns them a “cost” – a lower cost means faster connection.
     • Route-finding algorithms are used to determine which route through the mesh will have the lowest cost, and therefore take least time As the costs change because nodes become more or less busy, new routes are needed

3. ADADVANTAGES OF NERWORKS

   • Consistent User Experience
   • Your files are available on every computer you use,
   • You can print, use the Internet, email and use the same software on any computer

4. DISADVANTAGES OF NETWORKS

   • Expensive – extra hardware and wiring needed More room for error – if something goes wrong it can affect every computer Difficult – it requires a technical expertise Malware – viruses and other malicious software can spread through the network

5. WAN

   • Expensive – extra hardware and wiring needed More room for error – if something goes wrong it can affect every computer Difficult – it requires a technical expertise Malware – viruses and other malicious software can spread through the network

6. LAN

   • LOCAL AREA NETWORK

7. RING

   • ADVANTAGES
     • Cheap to install (one cable per computer) No collisions - only one computer is transmitting on each cable
   • DISADVANTAGES
     • High chance of catastrophic failure (if any cable breaks or any computer goes down, the entire network fails Difficult to add new computers

8. BUS

   • ADVANTAGES
     • Cheap to install (only one wire needed)
   • DISADVANTAGES
     • High chance of catastrophic failure (a break in the central cable takes out the entire network) High chance of collisions (multiple communications on the same cable that corrupt each other, slowing down the network) More computers mean more collisions, so the network gets slower as it gets bigger

9. STAR

   • ADVANTAGES
     • Fast (low chance of collisions) Easy to add new computers Low chance of catastrophic failure (a broken cable only takes out one computer, the rest of the network is fine)
   • DISADVANTAGES
     • Expensive (needs a lot of cabling, and a central switch, which is expensive) Failure of the switch will take down the network

10. ADRESSING

    • An address is a unique identifier given to something A house address (such as 15 High Street, Townsville) is an example of an address – each address is unique and used to identify that house

11. IP ADRESS

    • Computers on a network also need an address to identify them When a computer is added to a network it is assigned an IP Address (Internet Protocol Address) The IP Address is unique value assigned to each computer on a network Each IP address on a network must be unique
    • An IP Address is a unique value assigned to every computer on a network, used to identify it Messages on a network have an IP address attached, which is how a computer knows whether or not to keep the message
    • When the format of IP Addresses were decided in 1983, 4 billion addresses seemed more than enough In 1983, the concept of a network with more than 4 billion computers on it was laughable