This enables or disables Forward Error Correction (FEC) on the upstream direction of ONUs using this line profile, per the object's name and its EponSwitch syntax (the description is only the placeholder 'Description.'). FEC trades a small amount of usable bandwidth for the ability to correct bit errors in the optical upstream signal without retransmission, so this is the setting an admin turns on for ONUs experiencing marginal optical signal quality, for example long fiber runs or high splitter loss, at the cost of slightly reduced effective throughput on those lines. Enabling FEC on a line profile serving ONUs at the far end of a long, high-loss PON split could turn a marginal, error-prone upstream link into a stable one, at the cost of a few percent of raw bandwidth.