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; this particular bin is a live counter that keeps accumulating until it is explicitly cleared rather than rolling over on a fixed schedule, so a large value mostly reflects how long it has been since the last clear. For a 900-second bin, an AS value of 848 would correspond directly to 52 unavailable seconds in that same window on this port.