A mathematic recipe that generates a specific value, called a checksum, based on the contents of a data frame. The Cyclical Redundancy Check (CRC) is calculated before transmission of a data frame and then included with the frame; on receipt, the CRC is recalculated and compared to the sent value. If the two agree, the data frame is assumed to have been delivered intact; if they disagree, the data frame must be retransmitted.