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In this example, if the WRED profile applied to the port specifies a minimum and maximum queue thresh-
old of 30 and 70 percent:
•
The minimum queue length threshold is 3.6 MB (30% of 12MB).
•
The maximum queue length threshold is 8.4 MB (70% of 12MB).
If any NI is removed or inserted, this causes the addition or removal of Traffic Manager queues, which in
turn changes the aggregate maximum queue size. When this occurs, the system implicitly takes care of
adjusting all the WRED profile minimum and maximum threshold values to reflect the new aggregate
maximum queue size.
Queue Gain
The gain value is used to determine the instantaneous average queue length. The instantaneous average
queue length is a function of the previous average queue length and the current aggregate queue length
aggregated from all the Traffic Managers (nodes) in the system.
The higher the gain, the more of the previous average queue length is accounted for when computing the
instantaneous average queue length. A higher gain value helps the system to absorb bursts of traffic.
The lower the gain value, the more of the current queue length is accounted for when computing the
instantaneous average queue length. A lower gain value is useful when there is a stream with a steady flow
rate of traffic. However, if the gain value is too low, the system may not respond to congestion quickly
enough to initiate the random drops.
Configuring WRED Profiles
By default, WRP 1 is associated with each QSet profile and applied to each queue within the QSet
instance associated with the QSet profile. If the default profile is not sufficient, configuring up to three
additional profiles (WRP 2-4) is supported.
The default WRP 1 profile applies the following queue length thresholds, drop probability, and gain
parameter values:
Color
Min Queue
Green
Yellow
Red
Consider the following guidelines when configuring WRED profiles:
•
The default WRP 1 profile is not configurable and cannot be deleted from the switch configuration.
•
When a new profile is created, the default WRP 1 profile settings are imported into the new profile,
unless new parameters are specified at the time the profile is created.
•
Administratively disabling a profile is required before any changes can be made to the profile settings.
•
Configuring and applying queue threshold values is similar to configuring and applying bandwidth
shaping rates to limit bandwidth.
•
Configure the minimum queue threshold value large enough to account for bursty traffic. If this value
is too small, packet dropping will occur and may cause under utilization of the link.
OmniSwitch AOS Release 7 Network Configuration Guide
Max Queue
40
90
30
90
20
90
Drop Probability
24
30
36
March 2011
Gain
9
9
9
page 21-19
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