This Counter64 counts unavailable seconds at the physical TDM path layer underlying this pseudowire — time the TDM path itself, as opposed to the pseudowire service, was formally down. Because this is the cumulative TdmPwTotalStatistics counter for the pseudowire, tallied since the bin's own start time rather than being reset every short collection interval, Uasp isolates downtime caused by the TDM interface hardware/cabling from downtime caused by the packet network (which would instead show up in the PW-layer Uas counter), which matters for assigning the outage to the right team. For example, a nonzero Uasp during a window when the PW-layer Uas also shows unavailability points responsibility at the TDM circuit itself, whereas Uas alone incrementing without Uasp would point at the packet transport instead.