Brocade BigIron RX Series Configuration Guide - Manual (Page 590)

512 BigIron RX Series Configuration Guide
53-1002484-04
Traffic reduction parameters and algorithm
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Traffic reduction parameters and algorithm
A rate limiting policy specifies two parameters: requested rate and maximum burst.
Requested rate
The requested rate is the maximum number of bits a port is allowed to receive during a one-second
interval. The rate of the traffic that matches the rate limiting policy will not exceed the requested
rate.
The requested rate represents a percentage of an interface's line rate (bandwidth), expressed in
bits per second (bps).
Requested rate must be entered such that it is a divisor of 85333333 or 1333333. If the
requested rate is not a divisor of 85333333 or 1333333, the software adjusts the requested rate
down to the lowest divisor of 85333333 or 1333333 whichever is closest to the actual rate.
Example 1
If you enter 100,000 kbps as requested rate, based on the rate-limit algorithm, 100000 is lesser
than 148148, so the adjusted rate is a divisor of 1333333 closest to 100000. Therefore, the
adjusted rate is 102564 kbps.
Example 2
If you enter 200,000 kbps as requested rate, based on the rate-limit algorithm, 200000 is greater
than 148148, so the adjusted rate is a divisor of 85333333 closest to 200000. Therefore, the
adjusted rate is 199843 kbps.
NOTE
When the requested rate is less than 4 kbps, then the rate is adjusted to 3 kbps.
Maximum burst
Maximum burst provides a higher than requested rate to traffic that meet the rate limiting criteria.
When the traffic on the port is less than the specified requested rate, the rate limiting policy can
accumulate credits up to a maximum, as specified in the maximum burst value. The accumulated
credit allows traffic to pass through the port for a short period of time, at a rate higher than the
average rate. The time period is determined by the amount of credit accumulated and the rate of
traffic passing through the port.
The maximum burst rate cannot be smaller than 1250 bytes.
Actual rate
The device determines actual rate limiting rates through the use of proprietary formulas built into
the packet processor hardware. The resulting rate that is the closest to the requested rate. This
leads to variable rate limiting granularities for rate limiting rates. The lower the configured rate
limiting rate, the finer the granularity; the higher the configured rate limiting rate, the larger the rate
increments. For example, at lower rates, say from 20,345 to 40, 330 bps, the configurable rate
limiting rates can increment by 1 bps, but at higher rate limiting rates, say between 4 Gbps to
line-rate, the configurable rates increment in the hundreds of Mbps.
The CLI shows actual rate as requested rate.