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PIR-Only and CIR Mode

The actual behavior of many CoS parameters, especially the shaping rate and guaranteed rate, depend on whether the physical interface is operating in PIR-only or CIR mode.

In PIR-only mode, one or more nodes perform shaping. The physical interface is in the 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 CIR 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 CIR mode, one or more nodes applies the guaranteed rates. 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).

Note:

For nodes that do not have a guaranteed rate configured, Juniper recommends that you configure a delay buffer rate with the same value as the shaping rate.