Computer Science (0984) 2023 - 2 Data Transmission 2-2

2-2 Methods of Error Detection

2-2-1 Understand the need to check for errors after data transmission and how these errors can occur

• Errors can occur during data transmission due to:
  • Interference
    • electrical interference can cause data to be corrupted or lost
  • Problems during packet switching
    • can lead to data loss or even data gain
  • Skewing of data
    • occurs duing parallel data transmission
    • Can cause data corruption if bits arrive out of synchronisation

2-2-2 Describe the processes involved in each of the following error detection methods for detecting errors in data after transmission: parity check (odd and even), checksum and echo check

• Parity Checks
  • Parity checking is used to check whether data has been changed or corrupted following transmission from one device to another.
  • An extra bit (the parity bit) is added to a string of binary code to ensure the number of 1-bits are either odd (odd parity) or even (even parity)
    
  • Drawbacks:
    • If two bits are transposed (change places) then the computer could be fooled into thinking the data is correct and not corrupted
    • If two random bits change state then the system could also be fooled
  • Parity Block check checks a virtual table (both rows and columns) 
    …