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This chapter introduces the queuing methods supported.
22.1 Queuing Method Overview
Queuing is used to help solve performance degradation when there is network congestion. Use the
Queuing Method screen to configure queuing algorithms for outgoing traffic. See also Priority
Queue Assignment in Switch Setup and 802.1p Priority in Port Setup for related information.
Queuing algorithms allow switches to maintain separate queues for packets from each individual
source or flow and prevent a source from monopolizing the bandwidth.
22.1.1 Strictly Priority Queuing
Strictly Priority Queuing (SPQ) services queues based on priority only. As traffic comes into the
Switch, traffic on the highest priority queue, Q7 is transmitted first. When that queue empties,
traffic on the next highest-priority queue, Q6 is transmitted until Q6 empties, and then traffic is
transmitted on Q5 and so on. If higher priority queues never empty, then traffic on lower priority
queues never gets sent. SP does not automatically adapt to changing network requirements.
22.1.2 Weighted Fair Queuing
Weighted Fair Queuing is used to guarantee each queue's minimum bandwidth based on its
bandwidth weight (portion) (the number you configure in the Weight field) when there is traffic
congestion. WFQ is activated only when a port has more traffic than it can handle. Queues with
larger weights get more guaranteed bandwidth than queues with smaller weights. This queuing
mechanism is highly efficient in that it divides any available bandwidth across the different traffic
queues. By default, the weight for Q0 is 1, for Q1 is 2, for Q2 is 3, and so on. Guaranteed quantum
is calculated as Queue Weight x 2048 bytes.
22.1.3 Weighted Round Robin Scheduling (WRR)
Round Robin Scheduling services queues on a rotating basis and is activated only when a port has
more traffic than it can handle. A queue is a given an amount of bandwidth irrespective of the
incoming traffic on that port. This queue then moves to the back of the list. The next queue is given
an equal amount of bandwidth, and then moves to the end of the list; and so on, depending on the
number of queues being used. This works in a looping fashion until a queue is empty.
Weighted Round Robin Scheduling (WRR) uses the same algorithm as round robin scheduling, but
services queues based on their priority and queue weight (the number you configure in the queue
Weight field) rather than a fixed amount of bandwidth. WRR is activated only when a port has
more traffic than it can handle. Queues with larger weights get more service than queues with
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