This reports the current depth, in packets, of the priority-3 transmit queue on the port, representing traffic one tier below priority-2 in the port's outbound scheduling. An admin uses it alongside the sibling queue-length objects to see whether lower-priority bulk traffic is being deprioritized as intended during congestion, without unduly starving it. For example, a sustained high lportQP3Len during business hours could mean priority-3, often best-effort, traffic is being crowded out by higher-priority classes and needs bandwidth reallocation.