This read-only 64-bit counter tallies unicast frames sent in the network-to-access direction on this port during the interval, per the description. Admins use this as the primary measure of normal downstream traffic delivered to the customer, distinct from broadcast or multicast frames. For example, a drop in this counter compared to the customer's usual baseline, with no drop in the broadcast/multicast counters, would point an admin toward a downstream unicast delivery problem specific to that customer.