The OptiX OSN 1500, OptiX OSN 2500, and OptiX OSN 9500 are deployed on a network. The 24-hour BER test is performed on the SDH line for three times. Each time the BER test is performed, the SDH analyzer reads certain B3 bit errors and unavailable seconds (UASs). Check the history performance events. It is found that the HPBBE performance events occur every day.