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Page 26 | AlliedWare Plus™ OS: Overview of QoS
Specifying which queues to act on
To specify which queues to configure, use the optional queues parameter:
awplus(config)#mls qos queue-set <1-4> queues ...
Specify the desired queues as a space-separated list. For example:
awplus(config)#mls qos queue-set <1-4> queues 1 3 4 ...
To configure all queues, leave out the queues parameter.
If you do not configure RED curve settings on all the queues in a queue set, the unconfigured
queues use the default settings—see page 23.
Specifying the thresholds
To specify the maximum and minimum thresholds for each bandwidth class, use the
command:
awplus(config)#mls qos queue-set <1-4> [queues <list>] threshold
<minimum-green-threshold> <maximum-green-threshold>
<minimum-yellow-threshold> <maximum-yellow-threshold>
<minimum-red-threshold> <maximum-red-threshold>
Each threshold is a value from
1
-
1
6000000 bytes.
Specifying the drop probability
To specify the drop probability for each bandwidth class, use the command:
awplus(config)#mls qos queue-set <1-4> [queues <list>]
drop-probability <green-drop-prob> <yellow-drop-prob> <red-drop-prob>
Each drop probability is a value from 0-
1
5. The drop probability is
1
00% for a setting of 0 and
halves for each integer value increase. The following table shows probability values for drop
values of 0 to 7.
Specifying the averaging factor
Dropping is based on the average queue length, which is calculated as:
New Average Queue Length =
(
1
-
1
/(2
n
)) * (Current Average Queue Length) +
1
/(2
n
) * (Current Queue Length)
where n is the averaging factor. If n is small, the average queue length follows the actual
queue length quickly and is more likely to cause global TCP synchronisation. A large value for
n means the average queue length follows the actual queue length slowly. This may prevent
global TCP synchronisation, but will drop more packets. The recommended averaging factor
is 9.
Drop value
0
1
234567...
% drop probability
1
00% 50% 25%
1
2.5% 6.25% 3.
1
25%
1
.562 0.78
1
...