Noise spikes and other types of interference can change 0's to 1's and 1's to 0's during transmission.
For example, a short 20 ms click on a telephone line is unlikely to disrupt voice communication, but if data is being set over the line at 28,800 bps, the click may destroy over 5700 data bits.
All error detection methods involve the transmission of redundant data.
Redundant data could be omitted and the communication can still take place.
Error checking schemes compare redundant data to see if they agree.
If they do agree, it is likely that no error has occurred.
If they do not agree, it is almost certain that an error has occurred.
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