Alcatel-Lucent 7450 Quality Of Service Manual page 680

Advanced QoS Policy Command Reference
A possible reason to define a maximum decrement limit is to allow a child queue or policer to hold on
to a portion of bandwidth that has been distributed by the parent virtual scheduler in case the child's
offered rate fluctuates in an erratic manor. The max-decrement limit has a dampening effect to changes
in the offered rate.
A side effect of using a maximum decrement limit is that unused bandwidth allocated to the child
queue or policer will not be given to another child as quickly. This may result in an underrun of the
virtual scheduler's aggregate rate.
The max-decrement limit has no effect on any increase in a child's offered rate. If the rate increase is
above the change sensitivity, the new offered rate is immediately used.
If the max-decrement command is used with a percent based value, the decrement limit will be a
function of the configured PIR value on the policer or queue. In this case, care should be taken that the
child is either configured with an explicit PIR rate (other than max) or the child's administrative PIR
is defined using the percent-rate command with the local parameter enabled if an explicit value is not
desired. When a maximum PIR is in use on the child, the system attempts to interpret the maximum
child forwarding rate. This rate could be very large if the child is associated with multiple ingress or
egress ports.
Except for the overall cap on the offered input into the virtual scheduler, the child's administrative PIR
has no effect on the calculated sensitivity if an explicit rate is specified.
If the child's administrative PIR is modified while a percent based max-decrement is in effect, the
system automatically uses the new relative maximum decrement limit value the next time the child's
offered rate is determined.
When the max-decrement command is not specified or removed, the virtual scheduler does not limit a
decreasing offered rate to a specific limit.
The no form of this command is used to remove any currently configured maximum decrement limit
for all child policers and queues associated with the policy.
Parameters percent-of-admin-pir — When the percent qualifier is used, this parameter specifies the
rate-in-kilobits-per-second — When the rate qualifier is used, this parameter specifies an explicit
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percentage of the child's administrative PIR that should be used as the decrement limit to
offered rate change. If a value of 100 or 100.00 is used, the system will interpret this
equivalent to no max-decrement.
Default None, the decrement limit percentage value must be specified
when the percent qualifier is used.
Values 1.00 to 100.00
number of kilobits-per-second (1000 bits-per-second) that should be as the child's offered
rate change sensitivity value. If a rate sensitivity of 0 is specified, the system interprets this
equivalent to no granularity.
Default None, the decrement limit value must be specified when the rate
qualifier is used.
Values 0 to 100,000,000
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