Queue Default Rates for the IQE PIC

The IQE PIC operates at the queue level as well as at the logical unit level. This section discusses how the IQE PIC derives hardware values from the user configuration parameters. First, the default behavior without explicit configuration is investigated, along with the rules used to derive hardware parameters from the scheduler map configuration of the transmit rate, shaping rate, and excess rate. For more information about configuring schedulers and scheduler maps, see Overview of Schedulers.

When you do not configure any class-of-service parameters , a default scheduler map is used to establish four queues: best-effort, expedited-forwarding, assured-forwarding, and network-control. Each queue has the default transmit rate, shaping rate, and excess rate shown in Table 77.

Table 77: Default Queue Rates on the IQE PIC

When you configure a scheduler map to change the defaults, the IQE PIC hardware derives the values for each of the three major parameters: transmit rate, shaping rate, and excess rate.

The transmit rate is determined as follows:

• If a transmit rate is configured, then:

  • If the transmit rate is configured as an absolute bandwidth value, the configured value is used by the hardware.
  • If the transmit rate is configured as a percentage, then the percentage is used to calculate an absolute value used by the hardware, based on the guaranteed rate (CIR) configured at the logical interface or physical interface level. The CIR itself can be a default, configured, or derived value.
  • If the transmit rate is configured as a remainder, then the remaining value of the logical interface (unit) guaranteed rate (CIR) is divided equally among the queues configured as remainder.
• If a transmit rate is not configured, then the default transmit rate is derived based on remainder (for backward compatibility).
• If an excess rate is configured on any of the queues in a scheduler map, then the transmit rate on the queue is set to 0.

The shaping rate is determined as follows:

• If a shaping rate is configured:

  • If the shaping rate is configured as an absolute bandwidth value, the configured value is used by the hardware.
  • If the shaping rate is configured as a percentage, then the percentage is used to calculate an absolute value used by the hardware, based on the guaranteed rate (CIR) configured at the logical interface or physical interface level. Although it seems odd to base a shaping rate (PIR) on the CIR instead of a PIR, this is done so the shaping rate can be derived on the same basis as the transmit rate.
• If a shaping rate is not configured, then the default shaping rate is set to the shaping rate configured at the logical interface or physical interface level.

The excess rate is determined as follows:

• If an excess rate is configured on a queue, the value is used to derive an excess weight used by the IQE PIC hardware. The excess weight determines the proportional share of the excess bandwidth for which each queue can contend. The excess rate can be:

  • Percentage in the range from 1 through 100. This value is scaled to a hardware excess weight. Excess rates can add up to more than 100% for all queues under a logical or physical interface.

• If an excess rate is not configured on a queue, then the default excess rate is one of the following:

  • If a transmit rate is configured on any of the queues, then the excess weight is proportional to the transmit rates. Queues that do not have a transmit rate configured receive a minimum weight of 1.
  • If a transmit rate is not configured on any of the queues, but some queues have a shaping rate, then the excess weight is proportional to the shaping rates. Queues that do not have a shaping rate configured receive a minimum weight of 1.
  • If no parameters are configured on a queue, then the queue receives a minimum weight of 1.

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