ZyXEL Communications ES-315 - Manual (Page 71)

ES-315/ES-315-F User’s Guide
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H A P T E R
12
Queuing Method
This chapter introduces the queuing methods supported.
12.1 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 the Basic > Switch Setup screen and 802.1p Priority in the
Basic > Port Setup screen 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.
12.1.1 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, Q3 is transmitted first. When that queue
empties, traffic on the next highest-priority queue, Q2 is transmitted until Q2 empties, and
then traffic is transmitted on Q1 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.
12.1.2 Weighted Fair Queuing
Weighted Fair Queuing is used to guarantee each queue's minimum bandwidth based on its
bandwidth weight (portion) 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 each queue is 1. 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 = 10 Mbps
1+2+3+4