V.42 - technical definition

The ITU-T Recommendation for an error correction protocol that addresses error detection and correction through packet retransmission. V.42 is implemented in modems with asynchronous-tosynchronous conversion capability. As a default error correction method,V.42 includes the link access procedure for modems (LAPM), which is based on the High-Level Data Link Control (HDLC) protocol. In the event that LAPM fails, modems implementing V.42 fall back to the Microcom Networking Protocol version 4 (MNP4). See also error control, HDLC, LAPM, MNP 4, modem, and protocol.