Priority Queuing
With Priority queuing, queues are assigned different priority values and
placed in one of four queues. The high-priority queue is a strict priority
queue, which means that it gets serviced before anything else until it is
empty. After that, each queue is serviced in turn, as long as the priority
queue remains empty. The lower-priority queues may never be serviced
if there is sufficient traffic in higher-priority queues (a condition called
“starvation”).
Round Robin Queuing
Round Robin queuing takes one packet from each queue and then starts
over. Each queue is serviced, none starve, but there is no way to prioritize
any of the traffic or apply any sort of differential treatment to it.
During times of interface congestion, Weighted Round Robin (WRR)
queuing weights queues, and more packets are sent from higher weighted
queues, thus giving them more bandwidth. However, the bandwidth allocations
are done in a way that might lead to more bytes being sent from some
queues than desired, which causes other packets to be delayed.