© 2006 Cisco Systems, Inc. All rights reserved. QoS v2.2—6-1

Congestion Avoidance

Configuring Class-Based Weighted RED

© 2006 Cisco Systems, Inc. All rights reserved. QoS v2.2—6-2

WRED Building Blocks

© 2006 Cisco Systems, Inc. All rights reserved. QoS v2.2—6-3

DSCP-Based WRED(Assured Forwarding)

© 2006 Cisco Systems, Inc. All rights reserved. QoS v2.2—6-4

• WRED takes the average queue size to determine the current WRED mode (no drop, random drop, full drop).

• High values of N allow short bursts.• Low values of N make WRED more burst-sensitive.• Default value (9) should be used in most scenarios.• Average output queue size with N=9 is

Qave(t+1) = Qave(t) * 0.998 + Qt * 0.002

Changing WRED Sensitivity to Bursts

random-detect exponential-weighting-constant nrandom-detect exponential-weighting-constant n

router(config-pmap-c)#