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 a single queue may have several different queue thresholds. Each queue threshold is associated to a particular traffic class.

For example, a queue may have lower thresholds for lower priority packet. A queue buildup will cause the lower priority packets to be dropped, hence protecting the higher priority packets in the same queue. In this way quality of service prioritization is made possible for important packets from a pool of packets using the same buffer.

It is more likely that standard traffic will be dropped instead of higher prioritized traffic.

Restrictions

On Cisco switches WRED is restricted to

• TCP/IP traffic. Only this kind of traffic indicates congestion to the sender to enable a reduction of the transmission rate.
• Non-IP traffic will be dropped more often than TCP/IP traffic because it is treated with the lowest possible precedence.