Class Fair Hierarchical Policing (CFHP)
Quality of Service Guide 849
Parent Policer Priority and Unfair Sensitive Discard
Thresholds
Priority level bandwidth control is managed on the parent policer through the use of
progressively higher discard thresholds for each in use priority level. Up to eight priority
levels are supported and are individually enabled per parent policer instance based on child
policer priority level association. When multiple child policers are associated with a parent
policer priority level, two separate discard thresholds are maintained for that priority level. A
lower “discard-unfair” threshold ensures that when a child policer has exceeded its FIR rate,
its unfair packets are discarded first (assuming the parent policer’s bucket depth has reached
the priority level’s “discard-unfair” threshold) protecting the priority level’s fair traffic from
the priority level’s unfair traffic.
A second “discard-all” threshold is used to discard all remaining packets associated with the
priority level in the case where higher priority traffic exists and the sum of both the priority
level’s traffic and the higher priority traffic exceeds the parent policer rate. This protects the
higher priority traffic on the parent policer from being discarded due to lower priority traffic.
The child and parent policers operate in an atomic fashion, any conform effect on a child
policer's bucket depth is canceled when the parent policer discards a packet. See Figure 56
for a description of policer bucket rate and packet flow interaction with bucket depth. See
Figure 57 for a description of parent policer bucket and priority thresholds.
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