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DGS-1520 Series Gigabit Ethernet Smart Managed Switch Web UI Reference Guide
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packets and their QoS queue to determine if there will be an overflow of packets entering the QoS queues and
consequentially, minimize the packet flow into these queues by dropping random packets.
WRED employs two methods of avoiding congestion within the QoS queue.
• Every QoS queue has a minimum and a maximum level for acceptance of packets. Once the maximum
threshold has been reached for this queue, the Switch will begin discarding all ingress packets, this minimizing
the allotted bandwidth for QoS. When below the minimum threshold, the Switch will accept all ingress packets.
• When the ingress packets are somewhere between the maximum and minimum queue, the Switch will use a
slope probability function to determine a random method of dropping packets based on the maximum drop rate
which specifies the drop probability when the queues reach maximum threshold. If queues are closer to the
maximum threshold, the Switch will increase the discarding of random packets to even out the flow to the
queues and avoid overflows to higher priority queues.
WRED Profile
This window is used to display and configure the Weighted Random Early Detection (WRED) profile settings.
To view the following window, click QoS > WRED > WRED Profile, as shown below:
Figure 7-26 WRED Profile Window
The fields that can be configured are described below:
Parameter Description
Profile
Enter the WRED profile ID here. The range is from 1 to 32.
Packet Type
Specifies that the packet type is TCP.
Packet Colour
Select the packet color here. Options to choose from are:
• Green - Specifies the WRED drop parameters for green packets to be set.
• Yellow - Specifies the WRED drop parameters for yellow packets to be set.
• Red - Specifies the WRED drop parameters for red packets to be set.
Min Threshold
Enter the minimum threshold value here that will be used to start WRED dropping.
The range is from 0 to 100.
Max Threshold
Enter the maximum threshold value here over which WRED will drop all packets
destined for this queue. The range is from 0 to 100.
Max Drop Rate
Enter the maximum drop-rate value here. The range is from 0 to 14. This feature
specifies the drop probability when the average queue size reaches the maximum
threshold. When this value is zero, then the packet will not be dropped or
remarked for ECN.
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