This is the aggregate counter summing all the various SMDS-related discard reasons on this interface, the screening failures, address-not-found conditions, invalid-field errors, and CRC errors covered by the more granular counters above, into a single top-level figure for how much traffic got dropped. An admin monitors this as a quick health dashboard metric, only drilling into the specific granular counters once this aggregate signals a problem worth investigating. For example, a sudden jump in lportSmdsTotalDiscards would prompt the admin to check the individual counters for screening fails, address-not-founds, and CRC errors to pin down exactly which discard reason is driving the spike.