This read-only Gauge reports the number of Severely Errored Seconds encountered by this DS1 interface in the current 15-minute interval, a stricter category than plain Errored Seconds that indicates seconds with a high enough error density (or loss of frame) to be considered severely degraded rather than just marginally imperfect. A rising dsx1CurrentSESs alongside dsx1CurrentESs indicates the errors aren't just occasional bit hits but clusters severe enough to likely cause actual application-level impact. An engineer distinguishing a link with minor noise from one experiencing real service-affecting problems would look at dsx1CurrentSESs specifically, since a link can have a nonzero ES count from isolated errors while still having zero SES.