Running pf_stat or nf_stat without an interval and count displays the total number of error frames received since the interface was activated. Running pf_stat or nf_stat with an interval and count displays the number of error frames received since the last interrogation. An error frame is defined as an SMT frame whose E (error) bit is set, and whose E bit is first detected by the local station. It does not indicate the location of the cause of the error. Frequent error frames can indicate a noise problem on the network, either dirt (optical fiber) or electrical interference (UTP).