Chapter 42 Configuring PFC QoS

Configuring PFC QoS

Allocating Bandwidth Between Standard Transmit Queues

The router transmits frames from one standard queue at a time using one of these dequeuing algorithms, which use percentages or weights to allocate relative bandwidth to each queue as it is serviced in a round-robin fashion:

•Shaped round robin (SRR)—SRR allows a queue to use only the allocated bandwidth. Supported as an option on Supervisor Engine 32 SFP 1p3q8t ports and on 1p7q4t ports.

•Deficit weighted round robin (DWRR)—DWRR keeps track of any lower-priority queue under-transmission caused by traffic in a higher-priority queue and compensates in the next round. DWRR is the dequeuing algorithm on 1p3q1t, 1p2q1t, 1p3q8t, 1p7q4t, and 1p7q8t ports.

Note You configure DWRR ports with the same commands that you use on WRR ports.

•Weighted round robin (WRR)—WRR allows a queue to use more than the allocated bandwidth if the other queues are not using any, up to the total bandwidth of the port. WRR is the dequeuing algorithm on all other ports.

With Release 12.2(18)SXF and later releases, you can enter percentages or weights to allocate bandwidth. With releases earlier than Release 12.2(18)SXF, you enter weights to allocate bandwidth.

The higher the percentage or weight that is assigned to a queue, the more transmit bandwidth is allocated to it. If you enter weights, the ratio of the weights divides the total bandwidth of the queue. For example, for three queues on a Gigabit Ethernet port, weights of 25:25:50 provide this division:

•Queue 1—250 Mbps

•Queue 2—250 Mbps

•Queue 3—500 Mbps

Note The actual bandwidth allocation depends on the granularity that the port hardware applies to the configured percentages or weights.

 

Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX

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OL-4266-08

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Cisco Systems OL-4266-08 manual Allocating Bandwidth Between Standard Transmit Queues, 42-108
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OL-4266-08 specifications

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