Remember ... Priority-queue ...

Strict Priority Queue

A strict priority queue is always emptied first. So, as soon as there is a packet in the strict priority queue, the packet is forwarded. After each packet is forwarded from one of the WRR queues, the strict priority queue is checked and emptied if necessary.
A strict priority queue is specially designed for delay/jitter-sensitive traffic, such as voice. A strict priority queue can eventually cause starvation of the other queues. Packets that are placed in the three other WRR queues are never forwarded if a packet waits in the strict priority queue.