
Quality of Service (QoS)
©2008 Allied Telesis Inc. All rights reserved.
39.30
AlliedWare Plus
TM
Operating System Software Reference C613-50003-00 REV E
Software Version 5.2.1
Figure 39-12: Random Early Detect - Drop Profile
As the buffer further increases it will reach the point Max
th
. At this point the drop probability is
at the point Max_dp on the chart’s vertical axis. From this point on, any further increase in
queue size results in all packets in red traffic being dropped. This should increase the queue
queue space for the remaining yellow and green traffic.
If the queue continues to fill, the above situation will then apply to the yellow and green traffic,
as the queue size meets their own configurable thresholds Min
th
yellow, Max
th
yellow etc.
Setting these thresholds is covered in
“Configuring Tail Drop and Random Early Detection” on
page 39.30
.
Configuring Tail Drop and Random Early Detection
As previously mentioned the defaults for both drop methods can be seen from
Table 39-10
and
Table 39-11
. These tables show the same output for both tail-drop and RED detection
methods. However, when tail-drop is applied the values for Min
th
and average queue length
(Q
ave
) are ignored, and the drop probability is either 0 (for a current queue size
<Max
th
) or
100% (for for a current queue size >Max
th
).
The defaults shown are simply factory presets and are not intended to produce a functional
configuration. The information in this section is to provide the basic guidelines required for you
to set-up a tail-drop or RED detection method based on you own QoS standards.
Drop
Probability
%
100%
0%
Mi
n
Mi
n
Red
Red
th
th
Mi
n
Mi
n
Gree
n
Gree
n
th
th
Mi
n
Mi
n
Yellow
Yellow
th
th
Drop 3
Drop 3
Drop 2
Drop 2
Drop 1
Drop 1
Q
u
e
u
e Le
ng
th (bytes)
Max q
u
e
u
e le
ng
th
Max q
u
e
u
e le
ng
th
BW
Class Red
BW
Class Yellow
BW
Class Gree
n
QoS-WRED_RGY-Pro
f
ile
Max
Max
Red
Red
DP
DP
Max
Max
Yellow
Yellow
DP
DP
Max
Max
Gree
n
Gree
n
DP
DP
Max
Max
Gree
n
Gree
n
th
th
Max
Max
Yellow
Yellow
th
th
Max
Max
Red
Red
th
th