Samsung Ubigate iBG2016, Configuration Manual

Page: 243 / 744

Ubigate iBG2016 Configuration Guide/Ed.00
© SAMSUNG Electronics Co., Ltd.
207
Configuring RED parameters
This section discusses which RED parameters are configurable and how are
their default values set. It also explains the effect of changing these parameter
values and guidelines about how to set their values.
interface RED parameters
The EWF parameter determines the weight factor in the calculation of the
average queue size. The weight factor ‘w’ is calculated using the formula
(w = 1/(2^ewf)). The EWF parameter determines how RED is sensitive to
traffic fluctuations or bursts. If EWF is very low, then the RED is very
sensitive to traffic fluctuations and causes un-necessary early random packet
drops and there by reducing network throughput. If EWF is very high, then the
RED is not sensitive to traffic fluctuations and causes frequent tail drops
which reduces the effectiveness of RED. Therefore it is important to strike a
good balance in the value of EWF. The default value of ewf will be 5, which
means the actual EWF value = 1/32.
The MPD value determines the drop probability when the average queue size
is close to maxth. A high value will result in more aggressive drops for a given
increase in average queue size and could potentially lead to queue size
oscillations. A low value will result in a milder drop response for a given
increase in average queue size and increases the likelihood of tail drops.
Therefore it is important to select an optimum value. MPD is entered is
entered as a power of 2 and has a default value of 5. This means the actual
value of MPD = 32 and the Mark Probability = 1/32.
The minth and maxth, are the configured minimum and maximum thresholds
respectively, represents packet queue depth levels at which RED algorithm
changes its course of action, i.e. no-drop, probabilistic-drop, and tail-drop,
depending on whether the average queue size is below minth, in between
minth and maxth, and at or above maxth respectively.