Reference Guide

Quality of Service | 809

Allocate bandwidth to queue

The E-Series schedules unicast, multicast, and replication traffic for egress based on the Weighted Fair

Queuing algorithm. The C-Series and S-Series schedule packets for egress based on Deficit Round Robin

(DRR). These strategies both offer a guaranteed data rate.

To allocate an amount bandwidth to a queue using the command

bandwidth-percentage on the E-Series.

To allocate bandwidth to queues on the C-Series and S-Series, assign each queue a weight ranging from 1

to 1024, in increments of 2

, using the command bandwidth-weight. Table 44-3, "Default Bandwidth

Weights for C-Series and S-Series," in Quality of Service shows the default bandwidth weights for each

queue, and their equivalent percentage which is derived by dividing the bandwidth weight by the sum of all

queue weights.

There are two key differences between allocating bandwidth by weight on the C-Series and S-Series and

allocating bandwidth by percentage on the E-Series:

1. Assigning a weight to one queue affects the amount of bandwidth that is allocated to other queues.

Therefore, whenever you are allocating bandwidth to one queue, Dell Force10 recommends that you

evaluate your bandwidth requirements for all other queues as well.

2. Because you are required to choose a bandwidth weight in increments of 2

you may not be able to

achieve exactly a target bandwidth allocation.

Table 44-4, "Assigning Bandwidth Weights for the C-Series and S-Series," in Quality of Service shows an

example of choosing bandwidth weights for all four queues to achieve a target bandwidth allocation.

Table 44-3. Default Bandwidth Weights for C-Series and S-Series

Queue Default Weight Equivalent Percentage

0 1 6.67%

1 2 13.33%

2 4 26.67%

3 8 53.33%

Table 44-4. Assigning Bandwidth Weights for the C-Series and S-Series

Queue Weight Equivalent Percentage Target Allocation

0 1 0.44% 1%

1 64 28.44% 25%

2 128 56.89% 60%

3 32 14.22% 14%