IntroducingQoS

1、introduction to ip qosintroducing qosconverged networks quality issuesconverged network quality issues數(shù)量比較小的語音流量會和突發(fā)數(shù)據(jù)競爭網(wǎng)絡(luò)資源數(shù)量比較小的語音流量會和突發(fā)數(shù)據(jù)競爭網(wǎng)絡(luò)資源.管理流量應(yīng)該優(yōu)先獲得服務(wù)管理流量應(yīng)該優(yōu)先獲得服務(wù).語音和視頻流量應(yīng)該優(yōu)先獲得服務(wù)語音和視頻流量應(yīng)該優(yōu)先獲得服務(wù)converged network quality issues (cont.) lack of bandwidth（有限的帶寬）（有限的帶寬）: multiple flows compete f

2、or a limited amount of bandwidth. end-to-end delay (端到端延遲端到端延遲): packets have to traverse many network devices and links that add up to the overall delay. variation of delay (延遲的變化延遲的變化抖動抖動): sometimes there is a lot of other traffic, which results in increased delay. packet loss（數(shù)據(jù)包的丟失）（數(shù)據(jù)包的丟失）: pa

3、ckets may have to be dropped when a link is congested.available bandwidthlack of bandwidth最大帶寬數(shù)等于鏈路中的最小貸款最大帶寬數(shù)等于鏈路中的最小貸款.多種數(shù)據(jù)流競爭使用帶寬多種數(shù)據(jù)流競爭使用帶寬.bandwidth availability（解決帶寬不足）（解決帶寬不足）升級鏈路升級鏈路優(yōu)先轉(zhuǎn)發(fā)重要的數(shù)據(jù)優(yōu)先轉(zhuǎn)發(fā)重要的數(shù)據(jù)壓縮數(shù)據(jù)包壓縮數(shù)據(jù)包efficient use of available bandwidthusing advanced queuing and header compression

4、mechanisms, 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（處理延遲）（處理延遲）: the time it takes for a router to take the packet from an input interface

5、, examine it, and put it into the output queue of the output interface.queuing delay（隊列延遲）（隊列延遲）: the time a packet resides in the output queue of a router.serialization delay（串行化延遲）（串行化延遲）: the time it takes to place the “bits on the wire.”propagation delay（傳播延遲）（傳播延遲）: the time it takes for the pa

6、cket to cross the link from one end to the other.the impact of delay on qualityend-to-end delay（端到端延遲）（端到端延遲）=路徑上所有延遲的綜合路徑上所有延遲的綜合.jitter（抖動）（抖動） 是端到端延遲的變化是端到端延遲的變化.傳播延遲和串行化延遲是固定的傳播延遲和串行化延遲是固定的ways to reduce delay（減小延遲）（減小延遲）升級鏈路升級鏈路優(yōu)先轉(zhuǎn)發(fā)重要的數(shù)據(jù)包優(yōu)先轉(zhuǎn)發(fā)重要的數(shù)據(jù)包對重要的數(shù)據(jù)包重新定義優(yōu)先級對重要的數(shù)據(jù)包重新定義優(yōu)先級壓縮數(shù)據(jù)包壓縮數(shù)據(jù)包packet lo

7、ssimpact 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.)當(dāng)輸出隊列滿后，

8、路由器會執(zhí)行尾部丟棄當(dāng)輸出隊列滿后，路由器會執(zhí)行尾部丟棄. 尾部丟棄通常發(fā)生于鏈路擁塞時尾部丟棄通常發(fā)生于鏈路擁塞時ways to prevent packet loss（解決方法）（解決方法）升級鏈路升級鏈路為敏感數(shù)據(jù)包提供足夠的帶寬為敏感數(shù)據(jù)包提供足夠的帶寬在擁塞發(fā)生之前隨機丟棄數(shù)據(jù)包防止輸出隊列填滿在擁塞發(fā)生之前隨機丟棄數(shù)據(jù)包防止輸出隊列填滿implementing qosimplementing qos標(biāo)識標(biāo)識類型和需求類型和需求基于所標(biāo)識的需求信息對基于所標(biāo)識的需求信息對流量流量分類分類為每種類別定義相關(guān)為每種類別定義相關(guān)qos策略策略qos traffic classesthe r

9、equirements of different traffic typesidentify traffic and its requirementsnetwork audit（網(wǎng)絡(luò)審計）（網(wǎng)絡(luò)審計）: identify traffic on the network.business audit（業(yè)務(wù)審計）（業(yè)務(wù)審計）: determine how important each type of traffic is for business.service levels required（定義服務(wù)級別）（定義服務(wù)級別）: determine required response time.the

10、 requirements of different traffic typesqos policyqos policya networkwide definition of the specific levels of qos assigned to different classes of network trafficsummary converged networks that support voice, video, and data create new requirements for managing network traffic. qos meets those requ

11、irements. converged 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 to 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 requirem