Brocade Network OS Administrator’s Guide v4.1.1 - Manual (Page 477)

‐ 1-gigabit Ethernet
‐ 10-gigabit Ethernet
‐ 40-gigabit Ethernet
‐ 100-gigabit Ethernet
• BUM storm control and input service-policy are mutually exclusive features. Only one can be enabled
at a time on a given interface.
• BUM storm control replaces the multicast rate-limit feature for Brocade VDX 6740, VDX 8770-4 and
VDX 8770-8, and later platforms. This command is not supported on the Brocade VDX 6710, VDX
6720, and VDX 6730.
Scheduling
Scheduling arbitrates among multiple queues waiting to transmit a frame. The Brocade switch supports
both Strict Priority (SP) and Deficit Weighted Round Robin (DWRR) scheduling algorithms. Also
supported is the flexible selection of the number of traffic classes using SP-to-DWRR. When there are
multiple queues for the same traffic class, then scheduling takes these equal-priority queues into
consideration.
Strict priority scheduling
Strict priority scheduling is used to facilitate support for latency-sensitive traffic. A strict priority
scheduler drains all frames queued in the highest-priority queue before continuing on to service lower-
priority traffic classes. A danger with this type of service is that a queue can potentially starve out lower-
priority traffic classes.
The following figure displays the frame scheduling order for an SP scheduler servicing two SP queues.
The higher-numbered queue, SP2, has a higher priority.
FIGURE 53 Strict priority schedule — two queues
Weighted Round Robin scheduling
Weighted Round Robin (WRR) scheduling is used to facilitate controlled sharing of the network
bandwidth. WRR assigns a weight to each queue; that value is then used to determine the amount of
bandwidth allocated to the queue. The round robin aspect of the scheduling allows each queue to be
serviced in a set order, sending a limited amount of data before moving onto the next queue and cycling
back to the highest-priority queue after the lowest-priority queue is serviced.
The following figure displays the frame scheduling order for a WRR scheduler servicing two WRR
queues. The higher-numbered queue is considered higher priority (WRR2), and the weights indicate the
network bandwidth should be allocated in a 2:1 ratio between the two queues. In this figure WRR2
receives 66 percent of the bandwidth and WRR1 receives 33 percent. The WRR scheduler tracks the
extra bandwidth used and subtracts it from the bandwidth allocation for the next cycle through the
queues. In this way, the bandwidth utilization statistically matches the queue weights over longer time
periods.
Scheduling
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