The Frame Check Sequence (FCS) is a method used by both the sender and receiver to verify the integrity of a data frame during transmission. The sender calculates an FCS value using a specific algorithm, typically a cyclic redundancy check (CRC), and appends it to the end of the data frame before transmission.
The receiver also uses the same algorithm to calculate an FCS value based on the received data frame. If the calculated FCS value matches the one appended by the sender, it indicates that the data frame was not altered during transmission. If the FCS values do not match, it indicates that the data frame may have been corrupted and needs to be retransmitted.
By using the same formula to calculate the FCS value, both the sender and receiver can ensure the data integrity of the transmitted frames.