ZyXEL Communications MES3500-24, User Manual

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MES3500-24/24F User’s Guide
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H A P T E R
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Queuing Method
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 (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. By default, the weight for Q0 is
1, for Q1 is 2, for Q2 is 3, and so on.
The weights range from 1 to 15 and the actual guaranteed bandwidth is calculated as follows:
2
(Weight -1)
x 10 KB
If the weight setting is 5, the actual quantum guaranteed to the associated queue would be as
follows:
2
4
x 10KB = 160 KB