Brocade TurboIron 24X Series Configuration Guide - Manual (Page 1079)

Brocade TurboIron 24X Series Configuration Guide 1045
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Scheduling
• qosp3
• qosp2
• qosp1
• qosp0
Scheduling
Scheduling is the process of mapping a packet to an internal forwarding queue based on its QoS
information, and servicing the queues according to a mechanism.
QoS Queuing methods
The following QoS queuing methods are supported.
• Weighted round robin (WRR) – WRR ensures that all queues are serviced during each cycle. A
weighted fair queuing algorithm is used to rotate service among the eight queues on the
devices. The rotation is based on the weights you assign to each queue. This method rotates
service among the queues, forwarding a specific number of packets in one queue before
moving on to the next one.
WRR is the default queuing method and uses a default set of queue weights.
The number of packets serviced during each visit to a queue depends on the percentages you
configure for the queues. The software automatically converts the percentages you specify into
weights for the queues.
NOTE
Queue cycles on the devices are based on bytes. These devices service a given number of
bytes (based on weight) in each queue cycle.
• Strict priority(SP) – SP ensures service for high priority traffic. The software assigns the
maximum weights to each queue, to cause the queuing mechanism to serve as many packets
in one queue as possible before moving to a lower queue. This method biases the queuing
mechanism to favor the higher queues over the lower queues.
For example, strict queuing processes as many packets as possible in qosp3 before processing
any packets in qosp2, then processes as many packets as possible in qosp2 before processing
any packets in qosp1, and so on.
• Hybrid WRR and SP – An additional configurable queueing mechanism combines both the
strict priority and weighted round robin mechanisms. The combined method enables the
device to give strict priority to delay-sensitive traffic such as VOIP traffic, and weighted round
robin priority to other traffic types.
By default, when you select the combined SP and WRR queueing method, the device assigns
strict priority to traffic in qosp7 and qosp6, and weighted round robin priority to traffic in qosp0
through qosp5. Thus, the device schedules traffic in queue 7 and queue 6 first, based on the
strict priority queueing method. When there is no traffic in queue 7 and queue 6, the device
schedules the other queues in round-robin fashion from the highest priority queue to the
lowest priority queue.