This read-only PerfTotalCount reports the number of seconds the DSL port was enabled during the associated period, scoped to the most recent rolling 24-hour period ending at the moment of the poll. 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 pulling this rolling 24-hour up-time total can compute a trailing 24-hour availability percentage for an SLA report generated at any time of day.