Queue

The device supports 8 queues for each interface. Queue number eight is the highest priority queue. Queue number one is the lowest priority queue.

There are two ways of determining how traffic in queues is handled, Strict Priority and Weighted Round Robin (WRR).

  • Strict Priority—Egress traffic from the highest-priority queue is transmitted first. Traffic from the lower queues is processed only after the highest queue has been transmitted, thus providing the highest level of priority of traffic to the highest numbered queue.

  • Weighted Round Robin (WRR)—In WRR mode the number of packets sent from the queue is proportional to the weight of the queue (the higher the weight the more frames are sent). For example, if there are a maximum of four queues possible and all four queues are WRR and the default weights are used, queue 1 receives 1/15 of the bandwidth (assuming all queues are saturated and there’s congestion), queue 2 receives 2/15, queue 3 receives 4/15 and queue 4 receives 8 /15 of the bandwidth. The type of WRR algorithm used in the device isn’t the standard Deficit WRR (DWRR), but rather Shaped Deficit WRR (SDWRR).

The queuing modes can be selected in the Queue page. When the queuing mode is by strict priority, the priority sets the order in which queues are serviced, starting with the highest priority queue and going to the next lower queue when each queue is completed.

When the queuing mode is Weighted Round Robin, queues are serviced until their quota has been used up and then another queue is serviced. It’s also possible to assign some of the lower queues to WRR, while keeping some of the higher queues in strict priority. In this case traffic for the strict-priority queues is always sent before traffic from the WRR queues. Only after the strict-priority queues have been emptied is traffic from the WRR queues forwarded. (The relative portion from each WRR queue depends on its weight).

To select the priority method and enter WRR data, complete the following steps:

Procedure

Step 1

Click Quality of Service > General > Queue.

Step 2

Enter the parameters.

  • Queue—Displays the queue number.

  • Scheduling Method—Select one of the following options:

    • Strict Priority—Traffic scheduling for the selected queue and all higher queues is based strictly on the queue priority.

    • WRR—Traffic scheduling for the selected queue is based on WRR. The period time is divided between the WRR queues that aren’t empty, meaning they have descriptors to egress. This division happens only if the strict-priority queues are empty.

    • WRR Weight—If WRR is selected, enter the WRR weight assigned to the queue.

    • % of WRR Bandwidth—Displays the amount of bandwidth assigned to the queue. These values represent the percent of the WRR weight.

Step 3

Click Apply. The queues are configured, and the Running Configuration file is updated.