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QoS Overview
Frequently Used QoS Terms
The following terms are used in 7450 ESS Hierarchical QoS to describe the operation and
maintenance of a virtual scheduler hierarchy and are presented for reference purposes.
'Above CIR' distribution is the second phase of bandwidth allocation between a parent scheduler
Above CIR
Distribution
and its child queues and child schedulers. The bandwidth that is available to the parent scheduler
after the 'within CIR' distribution is distributed among the child members using each child's level
(to define strict priority for the above CIR distribution), Weight (the ratio at a given level with
several children) and the child's rate value. A rate value equal to the child's CIR value results in a
child not receiving any bandwidth during the 'above CIR' distribution phase.
Available bandwidth is the bandwidth usable by a parent scheduler to distribute to its child queues
Available
Bandwidth
and schedulers. The available bandwidth is limited by the parent's schedulers association with its
parent scheduler. If the parent scheduler has a parent of its own and the parent schedulers defined
rate value, then available bandwidth is distributed to the child queues and schedulers using a
'within CIR' distribution phase and an 'above CIR' distribution phase. Distribution in each phase
is based on a combination of the strict priority of each child and the relative weight of the child at
that priority level. Separate priority and weight controls are supported per child for each phase.
The Committed Burst Size (CBS) specifies the relative amount of reserved buffers for a specific
CBS
ingress network MDA forwarding class queue or egress network port forwarding class queue. The
value is entered as a percentage.
The Committed Information Rate (CIR) defines the amount of bandwidth committed to the
CIR
scheduler or queue.
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A child's (queue or scheduler) CIR is used with the CIR level parameter to determine the child's
committed bandwidth from the parent scheduler. When multiple children are at the same strict CIR
level, the CIR weight further determines the bandwidth distribution at that level.
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For schedulers, the CIR value can be explicitly defined or derived from summing the child
member CIR values.
On a queue, the CIR value is explicitly defined.
The CIR rate for ingress queues controls the in-profile and out-of-profile policing and
ultimately egress in-profile and out-of-profile marking. Queue CIR rates also define the
hardware fairness threshold at which the queue is no longer prioritized over other queues.
7450 ESS OS Quality of Service Guide
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