This counts seconds during which the emulated TDM circuit carried by this pseudowire was formally unavailable. UAS on this PW is the number that matters for an SLA on the emulated circuit, since it reflects seconds the TDM service was actually down, as opposed to merely having errored packets that the jitter buffer absorbed -- and this specific object covers a cumulative counter reset only by an explicit clear rather than on a fixed schedule -- reflecting everything since PM stats were last cleared. For example, since PM counters were last cleared, this pseudowire might show this counter at 100 -- a concrete count the admin can trend against neighboring bins to judge whether the condition it reflects is worsening.