Configuring WFQ参考.ppt

Implement the DiffServ QoS Model Configuring WFQ Weighted Fair Queuing A queuing algorithm should share the bandwidth fairly among flows by:加权公平队列算法能够在所有流中公平的平分接口带宽: Reducing response time for interactive flows by scheduling them to the front of the queue将交互式的流有计划的排列到队列前面从而减少响应时间. Preventing high-volume flows from monopolizing an interface阻止了大量的流强占某些端口. Weighted Fair Queuing (Cont.) In the WFQ implementation, conversations are sorted into flows and transmitted by the order of the last bit crossing its channel. Unfairness is reinstated by introducing weight to give proportionately more bandwidth to flows with higher IP precedence (lower weight). WFQ Architecture WFQ uses per-flow FIFO queues.WFQ基于每一个流启用单独的FIFO队列. WFQ Classification WFQ Classification (Cont.) A fixed number of per-flow queues is configured.不同的流队列配置不同的固定的编号. A hash function is used to translate flow parameters into a queue number.HASH函数被用于使用数据包中多个参数计算队列编号. System packets (eight queues) and RSVP flows (if configured) are mapped into separate queues.系统数据包(8个队列)和RSVP流(如果被配置)会被映射到单独的队列. Two or more flows could map into the same queue, resulting in lower per-flow bandwidth.一个或多个流可能被分配到相同队列,会导致流的带宽较低。 Important: The number of queues configured has to be significantly larger than the expected number of flows.重点：队列的数量配置要大于预期的流数量。 WFQ Insertion and Drop Policy WFQ has two modes of dropping:WFQ的两种丢弃模式: Early dropping when the congestive discard threshold is reached当达到拥塞丢弃门限值时丢弃数据包称为早期丢弃 Aggressive dropping when the hold-queue limit is reached当到达hold-queue限制时丢弃数据包称为主动丢弃 WFQ always drops packets of the most aggressive flow.WFQ始终丢弃大部分的侵略性流数据包. WFQ Insertion and Drop Policy (Cont.) Drop mechanism exceptions:例外的丢弃机制: A packet classified into an empty queue is never dropped.数据被分类到一个空队列,则不会被丢弃. The packet IP precedence has no effect on the dropping scheme.IP数据包的优先级不会影响WFQ的丢弃决策. Benefits and Drawbacks of WFQ Configuring WFQ cdt: Number of messages allowed in each queue (a new threshold must be a pow