This reports, in number of queued packets, how deep the priority-1 (highest priority) transmit queue currently is on this logical port. An admin monitors this to verify that latency-sensitive priority-1 traffic, often voice or signaling, is not backing up, since a persistently non-zero value here means even the top-priority queue cannot drain fast enough. For example, lportQP1Len holding steady at 40 packets while the link is supposedly not congested would indicate the priority-1 traffic volume itself now exceeds the port's outbound capacity.