This read-only PerfTotalCount reports the number of seconds the DSL port was enabled during the associated period, scoped to the DSL port's current, still-accumulating measurement period (not yet rolled into the interval history). Operationally, it's a direct availability measure, telling an admin how much of the period the port was actually usable rather than down or disabled. For example, an admin polling this counter can see exactly how many seconds into the current period the port has stayed up, confirming whether a recent flap has already been counted.