The 15 minute threshold associated with the number of severely errored frame seconds in the current interval. If the statistic exceeds this threshold value in the current interval a self-clearing alarm is raised. An severely errored frame second(SEFS) is defined as the number of seconds containing severely errored frames. Here, frames refer to MAC frames as opposed to, say, 8B/10B words. A 1-second interval is said to contain severely errored frames if 1% or more of the frames received in that interval contain errors.