WRED differs from other QoS techniques such as queuing because it attempts to anticipate and avoid congestion rather than controlling congestion after it has already begun to occur. It does this by selectively discarding lower-priority traffic when an output interface begins to get congested to ensure better overall session quality. This is because dropped TCP packets indicate congestion, signaling to the packet source to reduce its transmission rate. However, WRED is also useful for other types of flows. WRED is usually used in the core routers of a network, rather than at the network's edge.
Edge routers assign IP precedence to packets as they enter the network.
WRED uses the precedence information to determine how it treats different types of traffic. WRED treats non-IP traffic as precedence 0, the lowest precedence. Therefore, non-IP traffic is more likely to be dropped than IP traffic. The capability contributes significantly to a provider's ability to offer high service levels and differentiated services even during times of peak network usage. WRED selectively discards packets based on priority markings to prevent the router from dropping a large number of packets at the end of a transmission, which ensures session integrity, protects higher-priority traffic, and improves link efficiency.