This is a lifetime (cumulative, not interval-bound) count of how many times this SONET/SDH path has entered an AIS (Alarm Indication Signal) condition since the counter was last cleared. Unlike the 15-minute/day counters that reset on their own schedule, this figure keeps accumulating indefinitely, so an admin uses it to answer how many AIS events this path has ever had -- useful for spotting a chronically troublesome path when comparing its lifetime count against otherwise-similar paths on the same shelf. A reading of 340 on one path versus single digits on every neighboring path on the same card would single that path out as the one worth a physical inspection.