This counts Available Seconds on this SONET/SDH port for this bin: the seconds during the interval that were not counted as unavailable, per the MIB's description. AS is essentially the complement of UAS for this bin on this port -- it's the 'good time' denominator admins use alongside Total Time to compute the actual uptime percentage for this specific interval, rather than working the number backward from the unavailable count alone; because this bin spans the whole current day and is still open, short error bursts get averaged into a slower-moving daily total -- useful for spotting a low-grade, chronic problem that the 15-minute bins would report as merely noisy. For a 900-second bin, an AS value of 841 would correspond directly to 59 unavailable seconds in that same window on this port.