What happens if the FCS results do not match between the sender and receiver?

When the Frame Check Sequence (FCS) results do not match between the sender and receiver, it indicates that there has been an error in the transmission of the data frame. The FCS is a type of error-detecting code that is used to ensure data integrity during the transmission process. When the receiver calculates the FCS of the received frame and finds that it does not match the FCS value sent with the frame, it recognizes that the frame may have been corrupted during transmission.

In this situation, the correct response is that an error is detected, and the frame is discarded. This is a fundamental part of error control in data communication; by discarding frames that do not pass the FCS check, the network ensures that only valid and uncorrupted data is processed and delivered to the upper layers of the OSI model. This action helps maintain the integrity of the data being transmitted across the network.

Addressing this process also highlights the importance of protocols that manage retransmission of data. Some protocols may implement automatic retransmission for lost or corrupted frames, but the immediate response upon detecting a mismatch in FCS is to discard the problematic frame.