Depends on what you mean by DNDR FFC . DNDR is a digital set prompt that allows SCN appearances to start ringing after the DNDR value (6=1 ring, 12=2 rings,etc.) has expired. With FITA on the CLS you get intermittent, or continous ring on the set when it is off hook. (The reason for FITA in the first place) Without FITA on the set CLS you would still get just 1 buzz tone. The main purpose for DNDR is to allow the person who owns the DN time to answer before it starts to ring on a secty set who answers the call if that person doesn't. Most of the sectys like this because they don't stop every time their phone rings to see which Dn is ringing.