This counts the seconds in which this E1 port had at least one errored block. As the seconds-based counterpart to EB, ES on this port tells the admin how much of the elapsed time was affected by any error at all, the number typically compared against a G.826-style error-second-ratio threshold for the circuit -- 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 1 -- a concrete count the admin can trend against neighboring bins to judge whether the condition it reflects is worsening.