When a QSFP28-100G-LR4 optical module is used, the FEC function is disabled by default according to IEEE 802. It adds error-correction bits to data packets at the transmit end, which the receive end uses to correct bit errors during transmission. This function introduces slight. This chapter provides information on how to configure FEC on optica modules. What Is Forward Error Correction (FEC)? What Is Forward Error Correction (FEC)? Forward Error. After inserting a 100G transceiver, you might see: Nine times out of ten, this is an FEC mismatch between the transceiver and the host device. The sender sends the data together with a certain redundant error correction code.