F451 Data transmission

F451 Data transmission

1. LAN

   • Over a small area such as one building
   • Wired or wireless communication from a central pont
   • More secure
   • Needs no extra communication device
   • Requirements
     • Router/HUB
     • Switches
     • Network interface cards
     • Network OS

2. WAN

   • Geographically remote
   • Uses external communications
   • Subject to attack
   • Requiremants
     • Modem
     • Telephone or fibre optic cables

3. Different types data transmission

   • Serial
     • One bit at a time
     • Along single wire
   • Parallel
     • Multiple bits at a time
     • Multiple wires
   • Duplex
     • Full: simoultaniously
     • Half: one at a time
     • In both directions
   • Simplex
     • Transferred in one direction

4. Bit rate

   • Number of bits transferred per a second
   • Often known as baud rate
   • Larger amounts of data being transferred require higher bit rates

5. Errors in transmission

   • Parity checking
     • For every byte in a string, a bit (or parity bit) is added
     • To ensure total number of 1s is...
       • odd for odd parity
       • even for even parity
     • If error found, sender is asked to re-send offending byte
   • Echoing
     • Receiver "echoes" back everything to sender
     • Data re-sent if error found
     • Inefficient but occasionally used
   • Checksum
     • Mathematical calculation carried out on packet of data
     • Result added to packet and sent to reciver
     • Receiver carries out same calculation and compares it with the sent result
     • Receiver asks for it to be re-sent if they do not match

6. Switching

   • Packet
     • No established route
     • Each packet sent on individual routes
     • Cannot be easily intecepted
     • Need to be reordered when sent
     • Maximises use of network
   • Circuit
     • Established route
     • All packets sent on same route
     • Results in easy inteception
     • Remain in correct order
     • Ties up large areas of network
   • Sends fixed sized packets individually, one after the other

7. Protocols

   • Essential to ensure two devices communicate successfully
   • Physical
     • Physical connection between devices
     • Wireless or wired
     • Serial or parallel
     • Radio or microwave
     • Copper cable or fibre optic
   • Logical
     • Bit rate
     • Routing
     • Error correction technique
     • Packet size
     • Rules governing data
     • Flow control