Queue Parameters
24 Quality of Service Guide
When defining the PIR for a queue, the value specified is the administrative PIR for the
queue.The router has a number of native rates in hardware that it uses to determine the
operational PIR for the queue. The user has some control over how the administrative PIR is
converted to an operational PIR should the hardware not support the exact CIR and PIR
values specified. The interpretation of the administrative PIR is discussed below in
Adaptation Rule.
Adaptation Rule
The adaptation rule provides the QoS provisioning system with the ability to adapt specific
CIR and PIR defined administrative rates to the underlying capabilities of the hardware the
queue will be created on to derive the operational rates. The administrative CIR and PIR rates
are translated to actual operational rates enforced by the hardware queue. The rule provides
a constraint used when the exact rate is not available due to hardware implementation trade-
offs.
For the CIR and PIR parameters individually, the system will attempt to find the best
operational rate depending on the defined constraint. The supported constraints are:
• Minimum — Find the hardware supported rate that is equal to or higher than the
specified rate
• Maximum — Find the hardware supported rate that is equal to or lesser than the
specified rate
• Closest — Find the hardware supported rate that is closest to the specified rate
Depending on the hardware upon which the queue is provisioned, the actual operational CIR
and PIR settings used by the queue will be dependent on the method the hardware uses to
implement and represent the mechanisms that enforce the CIR and PIR rates.
As the hardware has a very granular set of rates, the recommended method to determine
which hardware the rate is used for a given queue is to configure the queue rates with the
associated adaptation rule and use the show pools output to display the actual rate achieved.
To illustrate how the adaptation rule constraints minimum, maximum and closest are
evaluated in determining the operational CIR or PIR, assume there is a queue on an IOM3-
XP where the administrative CIR and PIR values are 401 Mbps and 403 Mbps, respectively.
The following output shows the operating CIR and PIR rates achieved for the different
adaptation rule settings:
*A:PE# # queue using default adaptation-rule=closest
*A:PE# show qos sap-egress 10 detail | match expression "Queue-Id|CIR Rule"
Queue-Id : 1 Queue-Type : auto-expedite
PIR Rule : closest CIR Rule : closest
*A:PE#
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