This counts errored seconds at the TDM path layer carried over this pseudowire, as distinct from the ES counter which covers the emulated line/service layer. ESP on this PW isolates errors attributable to the framed TDM path riding inside the pseudowire, helping the admin tell a framing/payload issue on the TDM side apart from packet-transport problems like Miss or Underrun on the same PW -- and this specific object covers a closed 15-minute history bin -- a fixed, final count for one completed interval rather than something still changing. For example, over that completed 15-minute bin, this pseudowire might show this counter at 3 -- a concrete count the admin can trend against neighboring bins to judge whether the condition it reflects is worsening.