Labs 21 and 22 are quick labs focusing on Congestion Avoidance and Traffic Classification.
Congestion Avoidance = WRED, you can configure WRED directly under the interface or you can be more specific and use MQC to apply WRED to a specific set of traffic.
Traffic Classification can be done a number of ways, PBR, CAR (or Rate-limit), or MQC.
There's not much to say about these labs as they are quick and to the point.
