3Com 10014299 manual Wred Configuration, Enable the Wred, Function of the Interface, Enable Wred

WRED Configuration 699

■When the length of the queue is between the minimum threshold and maximum threshold, the WRED algorithm is used to calculate and determine whether the packet is dropped. The specific method is that each incoming packet is allocated with a random number, which is compared with the drop probability of the current queue, if it is larger than the drop probability, the packet is dropped. The longer the queue is, the higher the drop probability is--but there is a maximum drop probability.

When WRED and WFQ is cooperated, the flow based WRED can be implemented. During the classification, different flows have their own queues, for the flow with small traffic, as its queue length is always smaller, the drop probability will be smaller, too. However, as the flow with large traffic will have larger queue length, more packets are discarded, protecting the benefit of the flow with smaller traffic.

Different from RED, the random number generated by WRED is based on the IP priority, it considers the benefit of the high priority packets, and relatively reduce the drop probability of the high priority packets. The 3Com router takes WRED as its congestion avoidance policy.

WRED Configuration	WRED configuration includes:
	■ Enable the WRED Function of the Interface
	■ Configure Weight Factors when Calculating WRED Average Queue Length
	■ Set the Priority Parameters for WRED
Enable the WRED	WRED must first be enabled, and then other parameters related to WRED can be
Function of the Interface	configured.
	Please perform the following configurations in the interface view.
	Table 738 Enable WRED
	Operation	Command
	Enable the WRED function of the interface	qos wred
	Disable the WRED function on the	undo qos wred
	interface

Configure Weight

Factors when

Calculating WRED

Average Queue Length

By default, the system disables WRED so the queue avoids congestion by using the tail-drop policy.

WRED can only operate with WFQ, and cannot be used separately or coperated with other queue. Therefore, before the startup of WRED, WFQ must have been applied to the interface.

Enabling WRED can be effective only in all physical interfaces, while this command is ineffective in the logic interface.

Please perform the following configurations in the interface view.

Table 739 Configure the WRED Weighted Factor for Calculating the WRED Average Queue Length

Operation Command