This Counter64 counts unavailable seconds for this pseudowire at the PW/service layer — seconds during the cumulative bin in which the service was considered 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, Uas is what most availability SLAs are actually built on — every second counted here is a second the circuit-emulation service was not usable, as opposed to merely degraded. For example, a jump of 30 in this counter within a single 15-minute bin means half a minute of this pseudowire's service was formally unavailable during that window, which is the kind of event that should also show up as a customer-visible outage report.