Networks

Networks

1. LAN: Local Area Network

   • a network confined to one location or organisation
     • its resources are only accessible by computers on that LAN

2. WAN: Wide Area Network

   • a network of LANs spanning a wide area
     • the internet is an example of a WAN

3. topologies

   • bus
     • a single cable connects all the computers
       • all the clients and servers connect to this cable
         • terminators are attached to each end of the cable
           • adv
             • cheap, easy to install, no extra equipment required
           • dis
             • more computers means more collisions, damage to the wire results in catastrophic failure
   • ring
     • each computer is connected to two other computers in a ring formation
       • each computer receives signals from ones of its connected computers
         • if the data is for itself, it reads it, if not it transmits it to the next computer
           • the data travels round the ring in one direction until it reaches its intended recipient
             • adv
               • no collisions, as each cable only has one computer able to transmit on it, number of computers does not affect speed
             • dis
               • one faulty cable or computer will result in catastrophic failure, more difficult to add new computers
   • star
     • all computers are connected to a central hub or switch
       • a hub sends each message to all the other computers
         • a switch checks the address and sends it only to the correct one
           • adv
             • no collisions, failure of a cable or computer is not catastrophic, easy to add new computers
           • dis
             • expensive (requires hub/ switch and lots of cabling), failure of hub/switch is catastrophic and difficult/ expensive to fix
   • mesh
     • each computer is connected to on or more other computers
       • a full mesh has every computer connected to every other computer
         • a partial mesh has only some of the computers connected
           • adv
             • zero catastrophic failure - there are always alternative paths for data, multiple transmissions can happen simultaneously
           • dis
             • redundancy - lots of unnecessary connections, expensive, difficult to maintain and administer

4. circuit switching

   • a path across the network is established
     • that path is locked and remains open for the duration of the communication

5. path finding

   • routing
     • a cost is assigned to each connection in a mesh
       • route-finding algorithms are used to find the lowest cost route between two nodes

6. packet switching

   • the data is split into lots of small chunks called packets
     • each one is sent independently, likely using different paths
       • the pockets are re-assembled at the other side

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
   • wireless access point
     • a device that creates a wireless network and allows other devices to connect
   • network interface card
     • device that creates a wireless network and transfers their data to devices on other networks