networks

networks

1. topologies

   • bus topology
     • Cheap to install (only one wire needed)
     • 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
   • ring topology
     • Cheap to install (one cable per computer)
     • No collisions - only one computer is transmitting on each cable
     • High chance of catastrophic failure (if any cable breaks or any computer goes down, the entire network fails
     • Difficult to add new computers
   • mesh topology
     • Zero catastrophic failure – there are always alternative paths for data
     • Multiple transmissions can happen simultaneously
     • Redundancy - Lots of unnecessary connections
     • Data needs to be routed through the network, as there are multiple possible paths
   • Star topology
     • 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)
     • Expensive (needs a lot of cabling, and a central switch, which is expensive)
     • Failure of the switch will take down the network

2. LAN

   • Local Area Network
   • Works only in a small geographical region

3. WAN

   • Wide Area Network
   • Works over large geographical regions like continents

4. Circuit switching

   • Route locked until data transfer is complete
   • e.g. phone calls on phone network
   • Data arrives in the order it was sent
   • Data arrives at a consistent speed
   • Can start reading transmission as soon as first bit arrives, as data arrives sequentially
   • Only one transmission at a time along each channel – clogs the network

5. Packet switching

   • The data is split into lots of small chunks called packets.
   • Each one is sent independently, likely using different paths.
   • The packets are re-assembled at the other side
   • Multiple transmissions can happen simultaneously
   • Large transmissions don’t clog the network
   • Lag (a delay) is needed to allow several packets to arrive before reading, as the first packet sent may not be the first packet received

6. 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

7. Network hardware

   • Hub and switch
     • 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 sending them to every device it’s connected to
   • bridge and gateway
     • A bridge connects together two networks that use the same base protocols
     • A gateway connects together two networks that use different base protocols
   • Router
     • stores addresses of devices on its network and transfers their data to devices on another network
   • WAP and NIC
     • Wireless Access Point
       • device that creates a wireless network and allows other devices to connect
     • Network Interface Card
       • device that joins the network (wired or wireless) and connects to a computer or other device

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