The parity trick that answers “exactly where?” and not just “something is wrong” Why should you care? Every frame crossing a cable or the air faces noise from interference, loose connectors or even a microwave oven. One flipped bit can turn a transfer of 100 into 900. The link layer’s first duty is to notice damage, and the receiver usually discards the frame and asks for a resend. On satellite or noisy wireless links, resending is slow and may fail again, so it would be bette...