RIIM does not use FEC.
RIIM uses short packets, so if anything happens on the channel, much of the packet will be lost, so a re-transmission is smarter than trying to re-build a packet which we lost most of. FEC is used more when you have long packets because damage is done to a small part of the packet, then re-construction is feasible, and a re-transmission is a waste of time and bandwidth.
