思科QoS学习资料（英文版）A.ppt

IP Quality of Service Introduction Objectives Upon completing this module, you will be able to: Describe the need for IP QoS Describe the Integrated Services model Describe the Differentiated Services model Describe the building blocks of IP QoS mechanisms (classification, marking, metering, policing, shaping, dropping, forwarding, queuing) List the IP QoS mechanisms available in the Cisco IOS Describe what QoS features are supported by different IP QoS mechanisms Objectives Upon completing this lesson, you will be able to: Describe different types of applications and services that have special resource requirements List the network components that affect the throughput, delay and jitter in IP networks List the benefits of deploying QoS mechanisms in IP networks Name some QoS mechanisms available in Cisco IOS Describe typical enterprise and service provider networks and their QoS-related requirements Why IP QoS? Application X is slow! Video broadcast occasionally stalls! Phone calls over IP are no better than over satellite! Phone calls have really bad voice quality! ATM (the money-dispensing-type) are non-responsive! ... Because ... Application X is slow! (not enough BANDWIDTH) Video broadcast occasionally stalls! (DELAY temporarily increases – JITTER) Phone calls over IP are no better than over satellite! (too much DELAY) Phone calls have really bad voice quality! (too many phone calls – ADMISSION CONTROL) ATM (the money-dispensing-type) are non responsive! (too many DROPs) ... What Causes ... Lack of bandwidth – multiple flows are contesting for a limited amount of bandwidth Too much delay – packets have to traverse many network devices and links that add up to the overall delay Variable delay – sometimes there is a lot of other traffic which results in more delay Drops – packets have to be dropped when a link is congested Available Bandwidth Maximum available bandwidth equals the bandwidth of the weakest link Multiple flows are contesting for the same bandwi