The default port scheduler H-QoS algorithm distributes bandwidth to its members by performing two allocation passes, one within CIR and one above CIR. Within each pass, it loops through the bandwidth distribution logic for its members by allocating bandwidth that is either consumed or unconsumed by each member (based on the member offered rate).
A second algorithm allows user control of the amount of bandwidth in excess of the offered rate that is given to a queue. In this algorithm, the unconsumed bandwidth is only distributed at the end of each pass and not during the loops within the pass. The algorithm is configured within the port scheduler configuration as follows:
configure qos port-scheduler-policy hqos-algorithm above-offered-allowance-control
When the above-offered-allowance-control H-QoS algorithm is selected, the port scheduler is supported on both Ethernet Vports and Ethernet physical ports with queues and schedulers parented to the port scheduler.
The distribution of unconsumed bandwidth for parented queues and schedulers is determined by the following parameters in an advanced configuration policy (see Port scheduler above offered allowance control):
configure
qos
adv-config-policy
child-control
bandwidth-distribution
above-offered-allowance
unconsumed-agg-rate percent <percent-of-unconsumed-agg-rate>
delta-consumed-agg-rate percent <percent-of-delta-consumed-agg-rate>
unconsumed-higher-tier-rate percent <percent-of-unconsumed-higher-tier-rate>
delta-consumed-higher-tier-rate percent <percent-of-delta-consumed-high-tier-rate>
The distribution of unconsumed bandwidth can be configured separately for aggregate rates (applied at the egress of a SAP or subscriber profile) and higher-tier rates (Vport aggregate rate and port scheduler level, group, and maximum rates). This is useful because there are normally only a few members of an aggregate rate but likely more members of a Vport or port scheduler.
For the aggregate and all higher-tier rates, the algorithm uses:
the percentage of the unconsumed bandwidth at that tier that can be given to the queue or scheduler. If there is unconsumed bandwidth at the end of a bandwidth distribution pass, then the configured percentage of this bandwidth is used in the subsequent processing. For the higher tiers, the value is the minimum of the unconsumed bandwidth at each tier. Configure higher percentages when a large portion of the aggregate rate and higher-tier rates are unconsumed.
the percentage of the delta of consumed bandwidth at that tier that can be given to the queue or scheduler. The delta of consumed bandwidth is determined by subtracting the bandwidth consumed by the other members of the rate (not including that consumed by this queue or scheduler) at the beginning of the pass from that at the end of the pass. This aspect allows a queue or scheduler to be given additional operational PIR when the rate at the tier is mostly consumed but the queue or scheduler itself does not have a high offered rate compared to its maximum rate. In these cases, most of the available rate is being consumed so the configured percentages are low, particularly for the higher-tier rates with many members.
The algorithm takes the maximum of the consumed bandwidth and delta of consumed bandwidth for each of the aggregate rate and higher-tier rates. Then the algorithm uses the minimum of these rates to set the queue or scheduler operational PIR. See Table: Default values of the percentages for information about the default values for the percentages.