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 the current, still-open 15-minute interval -- a value that keeps climbing until the interval closes and rolls into history. For example, so far in the current, still-running 15-minute interval, this E1 port might show this counter at 2 -- a concrete count the admin can trend against neighboring bins to judge whether the condition it reflects is worsening.