ZyXEL Communications OLT2406, User Manual

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Chapter 74 Queuing Method
OLT2406 User’s Guide
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HAPTER
74
Queuing Method
74.1 Queuing Method Overview
This chapter introduces the queuing methods supported.
Queuing is used to help solve performance degradation when there is network congestion. Queuing
algorithms allow switches to maintain separate queues for packets from each individual source or flow
and prevent a source from monopolizing the bandwidth.
74.1.1 Strictly Priority
Strictly Priority (SP) services queues based on priority only. As traffic comes into the OLT, 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.
74.1.2 Weighted Fair Queuing
Weighted Fair Queuing (WFQ) is used to guarantee the minimum bandwidth of each queue 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
74.1.3 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 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.