Which of the following causes a single channel to report the BEFFEC_EXC alarm?

A single channel reporting the BEFFEC_EXC (Bit Error Forward Error Correction Excess) alarm can be caused by (D) the input optical power of an OTU board being too high or too low. Both extremes can degrade signal quality, causing excessive bit errors. Other causes such as signal attenuation, external environment issues, or faulty optical amplifiers can also impact performance but are less directly linked to BEFFEC_EXC alarms. HCIP-Transmission stresses maintaining proper optical power levels and equipment health to avoid such errors and ensure service quality.