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PIR-Only and CIR Mode Overview

 

The actual behavior of many CoS parameters, especially the shaping rate and guaranteed rate, depends on whether the physical interface is operating in one of the following modes:

PIR-only Mode

In PIR-only (peak information rate) mode, one or more nodes perform shaping. The physical interface is in PIR-only mode if no child (or grandchild) node under the port has a guaranteed rate configured. The mode of the port is important because in PIR-only mode, the scheduling across the child nodes is in proportion to their shaping rates (PIRs) and not the guaranteed rates (CIRs). This can be important if the observed behavior is not what is anticipated.

In PIR-only mode, nodes cannot send if they are above the configured shaping rate. Table 1 shows the mapping between the configured priority and the hardware priority for PIR-only.

Table 1: Internal Node Queue Priority for PIR-Only Mode

Configured Priority

Hardware Priority

Strict-high

0

High

0

Medium-high

1

Medium-low

1

Low

2

CIR Mode

In CIR (committed information rate) mode, one or more nodes applies a guaranteed rate and might perform shaping. A physical interface is in CIR mode if at least one child (or grandchild) node has a guaranteed rate configured. In addition, any child or grandchild node under the physical interface can have a shaping rate configured. Only the guaranteed rate matters. In CIR mode, nodes that do not have a guaranteed rate configured are assumed to have a very small guaranteed rate (queuing weight).

In CIR mode, the priority for each internal node depends on whether the highest active child node is above or below the guaranteed rate. Table 2 shows the mapping between the highest active child's priority and the hardware priority below and above the guaranteed rate.

Table 2: Internal Node Queue Priority for CIR Mode

Configured Priority of Highest Active Child Node

Hardware Priority Below Guaranteed Rate

Hardware Priority Above Guaranteed Rate

Strict-high

0

0

High

0

3

Medium-high

1

3

Medium-low

1

3

Low

2

3