This 64-bit counter tracks the aggregate number of unicast packets that higher-level protocols requested be transmitted, including those later discarded, combined across a stacked VLAN's outer tag and its inner VLANs. Admins use it alongside discard/error counters elsewhere in the router MIB to determine what fraction of attempted outbound unicast traffic on this QinQ interface actually succeeded versus was dropped. For example, if this counter grows steadily but subscriber-reported throughput lags, an admin would next check for outbound discards on the individual inner VLANs.