CITS3002 Computer Networks  
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The Physical Layer and Transmission Errors

  Speed Error Rate
Telephone cable: 105 - 108bps 1 in 105 bits
Shielded copper cable: 107 - 109bps 1 in 1012 - 1013 bits
Optical fibre: 109 - 1014bps 1 in 1016 - 1017 bits
Wireless systems: 106 - 1012bps 1 in 105 - 109 bits

Rates of transmission errors are described by their probability of occuring, or by their expected bit-error-rate (BER).

Transmission errors usually occur in bursts and are caused by:

  • Thermal background noise
  • Impulse noise, electrical arcing (~10ms duration)
  • Distorted frequency
  • Crosstalk between adjacent wires

Over a particular time interval, a burst begins at the first bit that is corrupted (inverted), and ends at the last bit corrupted - the bits between are not necessarily all modified.

CITS3002 Computer Networks, Lecture 2, The Physical Layer, Errors detection and correction, p3, 6th March 2024.