Queue scheduling

Packets are scheduled from queues by hardware schedulers based on the type of the queue (see Queue type) and the current scheduling rate of the queue compared to its operational CIR and FIR. This applies to unicast queues at both ingress and egress, and multipoint queues at ingress, but not to HSQ IOM queues.

The queue type should be chosen based on the kind of traffic in the forwarding classes mapped to the queue.

The hardware scheduler services queues to forward packets from them in a strict priority order, as follows:

• Ingress queues, in priority order:

  1. Expedited queues where the queue’s current scheduling rate is below its operational FIR

  2. Best effort queues where the queue’s current scheduling rate is below its operational FIR

  3. Expedited queues where the queue’s current scheduling rate is below its operational CIR

  4. Best effort queues where the queue’s current scheduling rate is below its operational CIR

  5. Expedited queues where the queue’s current scheduling rate is above both its operational FIR and CIR

  6. Best effort queues where the queue’s current scheduling rate is above both its operational FIR and CIR

• Egress queues, in priority order:

  1. Expedited queues where the queue’s current scheduling rate is below its operational FIR

  2. Best effort queues where the queue’s current scheduling rate is below its operational FIR

  3. Expedited queues where the queue’s current scheduling rate is below its operational CIR

  4. Best effort queues where the queue’s current scheduling rate is below its operational CIR

  5. Expedited queues where the queue’s current scheduling rate is above both its operational FIR and CIR

  6. Best effort queues where the queue’s current scheduling rate is above both its operational FIR and CIR