ZyXEL Communications MES-2110, User Manual

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MES-2110 User’s Guide
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H A P T E R
19
QoS
19.1 Overview
Quality of Service (QoS) is used to prioritize source-to-destination traffic flows. All
frames in the flow are given the same priority. You can use QoS to give different
priorities to different frame types to solve performance degradation when there is
network congestion.
19.2 The QoS Base Configuration Screen
Queuing algorithms allow switches to maintain separate queues for frames from
each individual source or flow and prevent a source from monopolizing the
bandwidth.
All High Before Low Queuing
All high before low 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.
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 rather than a fixed amount
of bandwidth. WRR is activated only when a port has more traffic than it can