Configuring Low-Latency Static Policers on IQE PICs
You can rate-limit the strict-high and high queues on the IQE PIC. Without this limiting, traffic that requires low latency (delay) such as voice can block the transmission of medium-priority and low-priority packets. Unless limited, high and strict-high traffic is always sent before lower priority traffic, causing the lower priority queues to “starve” and cause timeouts and unnecessarily resent packets.
On the IQE PIC you can rate-limit queues before the packets are queued for output. All packets exceeding the configured rate limit are dropped, so care is required when establishing this limit. This model is also supported on IQ2 PICs and is the only way to perform egress policing on IQE PICs. This feature introduces no new configuration statements.
Although intended for low-latency traffic classes such as voice, the configuration allows any queue to be rate-limited. However, the configuration requires the rate-limited queue to have either a high or strict-high priority.
 | Note: You can configure a low-latency static policer for only one rate-limited queue per scheduler map. You can configure up to 1024 low-latency static policers. |
This example limits the transmit rate of a strict-high expedited-forwarding queue to 1 Mbps. The scheduler and scheduler map are defined, and then applied to the traffic at the [edit interfaces] and [edit class-of-service] hierarchy levels:
You can issue the following operational mode commands to verify your configuration (the first shows the rate limit in effect):
- show class-of-service scheduler-map scheduler-map-name
- show class-of-service interface interface-name
