ZyXEL Communications MGS-3712, User Manual

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MGS-3712/MGS-3012F User’s Guide
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H A P T E R
20
Queuing Method
This chapter introduces the queuing methods supported.
20.1 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.
20.1.1 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.
20.1.2 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 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 smaller weights. This queuing mechanism is highly efficient in
that it divides any available bandwidth across the different traffic queues and returns to queues
that have not yet emptied.