RED takes advantage of TCP s congestion control mechanism. By randomly dropping packets prior to periods of high congestion, RED tells the packet source to decrease its transmission rate. Assuming the packet source is using TCP, it will decrease its transmission rate until all the packets reach their destination, indicating that the congestion is cleared. You can use RED as a way to cause TCP to back off traffic. TCP not only pauses, but it also restarts quickly and adapts its transmission rate to the rate that the network can support.
RED distributes losses in time and maintains normally low queue depth while absorbing spikes.
When enabled on an interface, RED begins dropping packets when congestion occurs at a rate you select during configuration. RED is not recommended for protocols, such as AppleTalk or Novell Netware, that respond to dropped packets by retransmitting the packets at the same rate. This combination provides for preferential traffic handling for higher priority packets. It can selectively discard lower priority traffic when the interface begins to get congested, and provide differentiated performance characteristics for different classes of service. WRED differs from other congestion management techniques such as queuing strategies because it attempts to anticipate and avoid congestion rather than controlling congestion once it occurs.