This is the count of Errored Seconds the remote SONET terminal has reported back to this box, via far-end block error overhead, during the currently-accumulating 15-minute window. Because this number reflects errors the far end is seeing on signal received from this box (or in its own local receiver), a rising far-end count with a clean near-end count points an admin toward a transmit-side problem on this local card or a receiver problem at the far end, rather than a problem with what this box is receiving. If this climbs to 40 while the corresponding near-end ESs stays at 0, that asymmetry suggests checking this box's transmit optics or the outbound fiber run rather than the inbound one.