This Counter64 reports the number of seconds during the current measurement interval that this pseudowire's TDM path was counted as available (not in an unavailable/fault state). Because this is the live, currently-accumulating count for the pseudowire's TDM path layer in the present measurement interval, dividing this value by the matching Ttp (path total time seconds) counter gives you the path's availability percentage for that window, which is the number an SLA is usually measured against. For example, an Asp of 890 seconds against a Ttp of 900 seconds for a 15-minute bin works out to about 98.9% availability for that interval — comfortably inside a typical 99.9% monthly SLA only if such gaps stay rare.