Introducing QoS参考.ppt

Introduction to IP QoS Introducing QoS Converged Network Quality Issues Converged traffic characteristics:聚合流量特征: Constant small-packet voice flow competes with bursty data flow.恒定的语音小数据包流与突发数据量的带宽争用. Critical traffic must get priority.紧急流量必须拥有优先权. Voice and video are time-sensitive.延时敏感的语音和视频流. Brief outages are not acceptable.短暂故障是不可以接受的. Converged Network Quality Issues (Cont.) Lack of bandwidth: Multiple flows compete for a limited amount of bandwidth.可用的带宽:多种流量争用有限的带宽. End-to-end delay (fixed and variable): Packets have to traverse many network devices and links that add up to the overall delay.端到端的延时(固定和变化):数据包通过一些网络设备和链路会增加延时. Variation of delay (jitter): Sometimes there is a lot of other traffic, which results in increased delay.时延变化(抖动):当有其它流量存在时会导致延时加大. Packet loss: Packets may have to be dropped when a link is congested.丢包率:当链路拥挤时数据包会被丢弃. Lack of Bandwidth Maximum available bandwidth equals the bandwidth of the slowest link.最大可用的带宽等于链路上最小带宽. Multiple flows are competing for the same bandwidth, resulting in much less bandwidth being available to one single application.多种流量争用相同的带宽,结果是对于单个应用可用带宽变少. A lack in bandwidth can have performance impacts on network applications.带宽不足会导致延时,丢包以及很差的应用性能. Bandwidth Availability Upgrade the link (the best but also the most expensive solution).升级链路带宽(最有效也是最昂贵的解决方案) Forward the important packets first.优先转发重要的数据包. Compress the payload of Layer 2 frames (it takes time).压缩第二层帧的有效负载(导致延时). Compress IP packet headers.压缩IP数据包的包头. Efficient Use of Available Bandwidth Using advanced queuing and header compression mechanisms, the available bandwidth can be used in a much more efficient way:使用高级队列和报头压缩机制,提供足够带宽的有效方法: Voice: LLQ and RTP header compression语音: LLQ和RTP报头压缩 Interactive traffic: CBWFQ and TCP header compression交互式的流量: CBWFQ和TCP报头压缩 Types of Delay Processing delay: The time it takes for a router to take the packet from an input interface, examine it, and put it into the output queue of the output interfac