This counter accumulates the number of severely errored seconds (SES) on the local DS1 interface within the current 15-minute measurement window, defined as 1-second periods with at least 30% of blocks in error or signal loss. Severely errored seconds are a more serious indicator than simple errored seconds because they suggest the line is degrading rapidly or the far end is experiencing major issues. This real-time counter helps operators detect and respond to developing problems within minutes rather than hours.