This counts seconds in which this E1 port's error rate crossed the severe threshold -- a high proportion of errored blocks in that second, or a defect such as loss of frame. SES on this port is the counter unavailability is derived from (ten consecutive SES roll into UAS), so a sudden SES burst here is the leading indicator that this E1 link is about to be counted as formally unavailable -- and this specific object covers a cumulative counter reset only by an explicit clear rather than on a fixed schedule -- reflecting everything since PM stats were last cleared. For example, since PM counters were last cleared, this E1 port might show this counter at 60 -- a concrete count the admin can trend against neighboring bins to judge whether the condition it reflects is worsening.