3550 QOS : WRR

On 3550 : Weighted Round Robin is done per packet
On 6000/6500 : Weighted Round Robin is done by bandwidth

wrr-queue bandwidth 10 20 30 40

On gigabit ports:

The 4 queues could be assigned a different amount of buffer size and WRED or RED with 2 thershold by queues :

Wred :
wrr-queue random-detect max-threshold 1 50 100

Red :
wrr-queue threshold 1 50 100

Queue Size:
wrr-queue queue-limit Q_size1 Q_size2 Q_size3 Q_size4

On non-gigabit ports:

Only FiFO with a reserved number of packet by queues, (max 170) :

mls qos min-reserve level buffer_size
wrr-queue min-reserve level queue