On reception, each data word, with appended parity bit, is checked to see
how many 1s are present. For an even parity design, the number must be even. If it is
found to be odd, it can be concluded that at least one error has occurred during
transmission and the ARQ process can begin. Of course, if two bits are in error, the
parity check will pass, and the errors will go undetected.
The single bit parity check is thus best suited to low noise, low distortion links where
the error rate is known to be very low. For links with a high probability of error, more
sophisticated error checking methods must be used - the block or convolutional codes
described next, requiring the addition of larger numbers of redundant bits.
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