Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring QoS (Rev. 03)
Overview
© 2008 Foundry Networks, Inc.
Page 15 of 62
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0.5 0.75 0.875 0.9375 0.96875 0.984375 0.992188 0.996094 … 0.999969
Thus, setting a small value to the exponential weight factor
n
tends to cause large fluctuations as
traffic levels change. WRED will react quickly both to oncoming congestions and to the state when
the queue size has fallen back beneath the minimum threshold. However, if
n
is set to a value that
is too low, WRED might overreact to temporary traffic bursts and drop traffic unnecessarily.
Setting a large value to
n
tends to stabilize the average value and smoothen out peaks and troughs.
This will cause WRED to react slowly both to oncoming congestions and to the state when the
queue size has fallen back beneath the minimum threshold.
NOTE
If the user sets the exponential weight factor to a value that is too high, WRED will
not react to congestion. Packets will be sent or dropped as though WRED were not
activated.
Egress Traffic Shaping
When congestion occurs, the packets are transmitted on the outgoing interface and the assigned
queues. Traffic shaping allows the user to shape output traffic (egress traffic) on a per- port basis.
The output traffic is monitored to verify that it conforms to the rate configured on the device.
When excessive traffic is detected on the device, the output interface applies the traffic shaping and
controls the excess traffic. If the device queues overflow, the traffic is dropped.