Zyxel OLT2412 [155/326] Queuing method

Zyxel OLT2412 [155/326] Queuing method
OLT2412 User’s Guide 155
CHAPTER 22
Queuing Method
This chapter introduces the queuing methods supported.
22.1 Queuing Method Overview
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.
22.1.1 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.
22.1.2 Weighted Fair Queuing
Weighted Fair Queuing is used to guarantee each queue's minimum bandwidth 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
22.1.3 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

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