This read-only PerfTotalCount reports the number of seconds the DSL port was enabled during the associated period, scoped to the running total for the current calendar day so far. 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 checking today's running up-time total against the number of seconds elapsed since midnight can spot a partial outage that already happened earlier today.