WRED调度算法说明.pdfVIP

Distributed Weighted Random Early Detection Feature Summary Random Early Detection (RED) is a congestion avoidance mechanism that 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. Weighted RED (WRED) generally drops packets selectively based on IP precedence. Packets with a higher IP precedence are less likely to be dropped than packets with a lower precedence. Thus, higher priority traffic is delivered with a higher probability than lower priority traffic. However, you can also configure WRED to ignore IP precedence when making drop decisions so that non-weighted RED behavior is achieved. WRED is useful on any output interface where you expect to have congestion. However, WRED is usually used in the core routers of a network, rather than the edge. Edge routers assign IP precedences to packets as they enter the network. WRED uses these precedences to determine how it treats different types of traffic. The Distributed WRED (DWRED) feature uses the VIP rather than the RSP to perform the queuing; therefore, it requires a Cisco 7500 series router or Cisco 7000 series router with RSP7000. The Release 11.1 CC version of DWRED differs from the previously existing RSP-based version of W