Weighted random early detection

Weighted random early detection (WRED) is a queue management algorithm with congestion avoidance capabilities. It is an extension to Random early detection (RED) where different queues may have different buffer occupation thresholds before random dropping starts, as well as different dropping probabilities, and packets are classified into these queues according to priority information such as IP precedence or DSCP (for DiffServ). In this way QoS differentiation is made possible, since packets in queues with higher buffer occupation thresholds or lower dropping probabilities are effectively prioritized.

you can refer to Cisco web site about more details about Cisco routers implementing WRED http://www.cisco.com/en/US/docs/ios/11_2/feature/guide/wred_gs.html