Rate Limit - HP 1920 Gigabit Ethernet Switch Series User Manual

A typical switch provides eight output queues per port. WRR assigns each queue a weight value
(represented by w7, w6, w5, w4, w3, w2, w1, or w0) to decide the proportion of resources assigned to
the queue. On a 100 Mbps port, you can set the weight values of WRR queuing to 25, 25, 15, 15, 5,
5, 5, and 5 (corresponding to w7, w6, w5, w4, w3, w2, w1, and w0, respectively). In this way, the
queue with the lowest priority is assured of at least 5 Mbps of bandwidth, and the disadvantage of SP
queuing (that packets in low-priority queues might fail to be served for a long time) is avoided.
Another advantage of WRR queuing is that while the queues are scheduled in turn, the service time for
each queue is not fixed. If a queue is empty, the next queue will be scheduled immediately. This improves
bandwidth resource use efficiency.
Basic WRR queuing contains multiple queues. You can configure the weight, percentage (or byte count)
for each queue, and WRR schedules these queues based on the user-defined parameters in a round robin
manner.
You can implement SP+WRR queue scheduling on a port by assigning some queues on the port to the SP
scheduling group when you configure WRR. Packets in the SP scheduling group are scheduled
preferentially by SP. When the SP scheduling group is empty, the other queues are scheduled by WRR.

Rate limit

Rate limit is a traffic control method using token buckets. The rate limit of a physical interface specifies the
maximum rate for forwarding packets (including critical packets). Rate limit can limit all the packets
passing a physical interface.
Traffic evaluation and token bucket
A token bucket can be considered as a container holding a certain number of tokens. The system puts
tokens into the bucket at a set rate. When the token bucket is full, the extra tokens will overflow.
Figure 460 Evaluate traffic with the token bucket
The evaluation for the traffic specification is based on whether the number of tokens in the bucket can
meet the need of packet forwarding. If the number of tokens in the bucket is enough to forward the
packets (usually, one token is associated with a 1-bit forwarding authority), the traffic conforms to the
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