ZyXEL Communications ZyXEL Dimension ES-2048 - Manual (Page 139)

ES-2048 User’s Guide
139
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H A P T E R
18
Queuing Method
This chapter introduces the queuing methods supported.
18.1 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.
18.1.1 Strictly Priority
Strictly Priority (SP) 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.
18.1.2 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 - see
Figure 68 on
page 141 ) 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 bandwidth is calculated as follows:
For example, using the default setting, Q0 on Port 1 gets a guaranteed bandwidth of:
Queue Weight x Port Speed
Total Queue Weight
1 x 100 Mbps = 3 Mbps
1+2+3+4+5+6+7+8