Networks

Networks

1. Topologies

   • Bus
     • One cable that is conected to the rest of the compounents with terminators at the end of the cable
     • Advantage
       • 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)
   • Ring
     • A ring topology connected the computers to each other in a ring
   • Star
     • All computers are connected to a central switch or hub. A switch checks the address of the message and directs it to the correct computer A hub directs every message to every computer on the network, and leaves it up to the computer to accept or reject it.
     • Advantages
       • Fast – no data collisions (no computers trying to transmit on the same cable)
       • Reliable – a broken cable won’t take out the whole network
       • Easy to identify faults – a good switch can cut the connection to a malfunctioning device
     • Disadvantage
       • Expensive to set up (needs a lot of cabling, and a central switch or hub)
       • The whole network depends on the switch or hub, if this fails, the network fails
       • It is possible to overload a switch if too much data is passing through it, causing slowdowns
   • Mesh
     • A full mesh has every computer connected to every other computer
     • a partial mesh, where each device is connected to one or more other devices
     • In a mesh network there are multiple possible paths between any two devices
     • Advantages
       • Almost impossible to break – if any node goes down, an alternative route is available
     • Disadvantages
       • Very complex, as route-finding is necessary to decide path for data
       • Many redundant connections that may rarely be used
     • Circuit Switching
       • A route through the network was found and locked for the duration of the transmission
       • This was not a good system – if a node went down, the transmission would have to start again
     • Packet Switching
       • The data is split into lots of small chunks called packets
         • Each packet is then sent independently, probably along a different route
           • If a transmission fails, only the one packet needs to be re-sent
       • An issue with packet switching is that packets may arrive out of order (since they took different routes) The packets need to be re-assembled at the other side
     • Pathfinding
       • A cost is assigned to each connection in a mesh Route-finding algorithms are used to find the lowest cost route between two nodes

2. LAN

   • A (Local Area Network) is a network within a single organisation or area (like this school) – these use a star topology

3. WAN

   • A WAN (Wide Area Network) is a network that spans a large area (like the Internet) – these use a mesh topology

4. Advantages

   • Data and resources can be shared across all computers easily
   • Networks are not limited to any geographical location meaning files can be shared with people in different regions
   • It allows for backups in different computers or in different buildings meaning data is safe from any physical harm.
   • Archiving can happen automatically.
   • Networks allow entire offices to move to a new location and continue working should the old office become unusable
   • Networks will usually work out cheaper in the long term, as resources can be shared, and employees are more productive

5. Disadvantages

   • It has weaker security as if one computer is compromised the entire network is at risk
   • Networks are expensive to run and require regular maintenance
   • Network managers need to be employed and a lot of equipment and infrastructure must be paid for during the set-up

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

7. Hardware

   • Switch
     • Routes packets round a network by analysing them and sending them to the device they are addressed to
   • Hub
     • Routes packets round a network by blindly sending them to every device it's connected to
   • Bridge
     • Connects together two networks that use the same base protocols
   • Gateway
     • Connects together two networks that use different base protocols
   • Router
     • Stores the addresses of computers on its network and transfers their data to devices on other networks
   • WAP
     • Wireless Access Point
       • A device that creates a wireless network and allows other devices to connect
   • NIC
     • Network Interface Card
       • A device that joins the network (wired or wireless) and connects to a computer or other divice