ZyXEL Communications Dimension GS-3012F, User Manual

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GS-3012F User’s Guide
Queuing Method 18-1
Chapter 18
Queuing Method
This chapter introduces SPQ and WFQ.
18.1 Introduction to Queuing
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.
The switch has eight physical queues, Q0 to Q7. Q7 has the highest priority and Q0 has the lowest.
Table 18-1 Physical Queue Priority
QUEUE PRIORITY
Q7 8 (highest)
Q6 7
Q5 6
Q4 5
Q3 4
Q2 3
Q1 2
Q0 1 (lowest)
18.1.1 Strict Priority Queuing (SPQ)
Strict 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. SPQ does not automatically adapt to changing network
requirements.
18.1.2 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 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