This read-write Integer32 (3-5), indexed per interface, sets the exponent used to compute the bit error rate threshold that defines a Signal Failure condition, where the configured value n yields a BER threshold of 10^-n. Because the valid range (3-5) is looser than the Sd threshold's range (5-9), Sf represents a coarser, more severe error rate than Sd. For example, setting pdnLinkFailureSfBerThreshold to 3 declares a signal failure once the bit error rate reaches roughly 1 error per thousand bits (10^-3), a much worse condition than the typical Sd threshold.