Pronounced lap em. An error control mechanism defined in the ITU-T V.42 Recommendation, LAPM employs a cyclic redundancy check (CRC) for error correction and automatic repeat request (ARQ) for error correction. In the event the LAPM fails, a V.42 modem falls back to the similar, but slower, Microcom Networking Protocol version 4 (MNP4). See also ARQ, CRC, error control, ITU-T, and V.42.