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1、Introduction to IP QoSIntroducing QoSConverged Networks Quality IssuesConverged Network Quality Issues数量比较小的语音流量会和突发数据竞争网络资源数量比较小的语音流量会和突发数据竞争网络资源.管理流量应该优先获得服务管理流量应该优先获得服务.语音和视频流量应该优先获得服务语音和视频流量应该优先获得服务Converged Network Quality Issues (Cont.)Lack of bandwidth（有限的带宽）（有限的带宽）: Multiple flows compete fo
2、r a limited amount of bandwidth.End-to-end delay (端到端延迟端到端延迟): Packets have to traverse many network devices and links that add up to the overall delay.Variation of delay (延迟的变化延迟的变化抖动抖动): Sometimes there is a lot of other traffic, which results in increased delay.Packet loss（数据包的丢失）（数据包的丢失）: Packet
3、s may have to be dropped when a link is congested.Available BandwidthLack of Bandwidth最大带宽数等于链路中的最小贷款最大带宽数等于链路中的最小贷款.多种数据流竞争使用带宽多种数据流竞争使用带宽.Bandwidth Availability（解决带宽不足）（解决带宽不足）升级链路升级链路优先转发重要的数据优先转发重要的数据压缩数据包压缩数据包Efficient Use of Available BandwidthUsing advanced queuing and header compression mech
4、anisms, the available bandwidth can be used in a much more efficient way:Voice: LLQ and RTP header compressionInteractive traffic: CBWFQ and TCP header compressionEnd-to-End DelayTypes of DelayProcessing delay（处理延迟）（处理延迟）: The time it takes for a router to take the packet from an input interface, ex
5、amine it, and put it into the output queue of the output interface.Queuing delay（队列延迟）（队列延迟）: The time a packet resides in the output queue of a router.Serialization delay（串行化延迟）（串行化延迟）: The time it takes to place the “bits on the wire.”Propagation delay（传播延迟）（传播延迟）: The time it takes for the packet
6、 to cross the link from one end to the other.The Impact of Delay on QualityEnd-to-end delay（端到端延迟）（端到端延迟）=路径上所有延迟的综合路径上所有延迟的综合.Jitter（抖动）（抖动） 是端到端延迟的变化是端到端延迟的变化.传播延迟和串行化延迟是固定的传播延迟和串行化延迟是固定的Ways to Reduce Delay（减小延迟）（减小延迟）升级链路升级链路优先转发重要的数据包优先转发重要的数据包对重要的数据包重新定义优先级对重要的数据包重新定义优先级压缩数据包压缩数据包Packet LossIm
7、pact of Packet LossTelephone call: “I cannot understand you. Your voice is breaking up.”Teleconferencing: “The picture is very jerky. Voice is not synchronized.”Publishing company: “This file is corrupted.”Call center: “Please hold while my screen refreshes.”Impact of Packet Loss (Cont.)当输出队列满后，路由器会
8、执行尾部丢弃当输出队列满后，路由器会执行尾部丢弃. 尾部丢弃通常发生于链路拥塞时尾部丢弃通常发生于链路拥塞时Ways to Prevent Packet Loss（解决方法）（解决方法）升级链路升级链路为敏感数据包提供足够的带宽为敏感数据包提供足够的带宽在拥塞发生之前随机丢弃数据包防止输出队列填满在拥塞发生之前随机丢弃数据包防止输出队列填满Implementing QoSImplementing QoS1.标识标识类型和需求类型和需求2.基于所标识的需求信息对基于所标识的需求信息对流量流量分类分类3.为每种类别定义相关为每种类别定义相关QoS策略策略QoS Traffic ClassesThe
9、 Requirements of Different Traffic TypesIdentify Traffic and Its RequirementsNetwork audit（网（网络审计）: Identify traffic on the network.Business audit（业务审计）: Determine how important each type of traffic is for business.Service levels required（定（定义服服务级别）: Determine required response time.The Requirements
10、 of Different Traffic TypesQoS PolicyQoS PolicyA networkwide definition of the specific levels of QoS assigned to different classes of network trafficSummaryConverged networks that support voice, video, and data create new requirements for managing network traffic. QoS meets those requirements.Conve
11、rged networks suffer from different quality issues, including lack of adequate bandwidth, end-to-end and variable delay, and lost packets.Packet loss can adversely affect QoS in a network.QoS is a way to improve the performance of converged networks.Summary (Cont.)Lack of recourses causes networks t
12、o experience different types of delay, including processing delay, queuing delay, serialization delay, and propagation delay.QoS traffic classes need to be defined to implement a QoS policy.Implementing QoS requires three steps: identify requirements, classify network traffic, and define networkwide policies for quality.A QoS policy is a networkwide definition of the specific levels of QoS assigned to classes of network traffic.
