#### Question 7.5 Question 7.6

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## Parity (cont.)

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. |

#### Shown here is a simple circuit for working out the necessary parity bit for even or odd parity and a seven-bit input data word.