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C H A P T E R

49

Chapter Goals
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Introduce QoS concepts. Define QoS tools. Discuss QoS tools capabilities. Discuss examples of QoS tool usage.

Quality of Service Networking
Introduction
Quality of Service (QoS) refers to the capability of a network to provide better service to selected network traffic over various technologies, including Frame Relay, Asynchronous TransferMode (ATM), Ethernet and 802.1 networks, SONET, and IP-routed networks that may use any or all of these underlying technologies. The primary goal of QoS is to provide priority including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics. Also important is making sure that providing priority for one or more flowsdoes not make other flows fail. QoS technologies provide the elemental building blocks that will be used for future business applications in campus, WAN, and service provider networks. This chapter outlines the features and benefits of the QoS provided by the Cisco IOS QoS.

Note

A flow can be defined in a number of ways. One common way refers to a combination of source and destinationaddresses, source and destination socket numbers, and the session identifier. It can also be defined more broadly as any packet from a certain application or from an incoming interface. Recent identification tools have allowed the definition of a flow to be performed more precisely (for instance, to the URL or MIME type inside an HTTP packet). Within this chapter, references to a flow could be any one ofthese definitions. The Cisco IOS QoS software enables complex networks to control and predictably service a variety of networked applications and traffic types. Almost any network can take advantage of QoS for optimum efficiency, whether it is a small corporate network, an Internet service provider, or an enterprise network. The Cisco IOS QoS software provides these benefits:


Control overresources—You have control over which resources (bandwidth, equipment, wide-area facilities, and so on) are being used. For example, you can limit the bandwidth consumed over a backbone link by FTP transfers or give priority to an important database access.

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Chapter 49 QoS Concepts

Quality of Service Networking



Moreefficient use of network resources—Using Cisco’s network analysis management and accounting tools, you will know what your network is being used for and that you are servicing the most important traffic to your business. Tailored services—The control and visibility provided by QoS enables Internet service providers to offer carefully tailored grades of service differentiation to their customers.Coexistence of mission-critical applications—Cisco’s QoS technologies make certain that your WAN is used efficiently by mission-critical applications that are most important to your business, that bandwidth and minimum delays required by time-sensitive multimedia and voice applications are available, and that other applications using the link get their fair service without interfering withmission-critical traffic. Foundation for a fully integrated network in the future—Implementing Cisco QoS technologies in your network now is a good first step toward the fully integrated multimedia network needed in the near future.

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QoS Concepts
Fundamentally, QoS enables you to provide better service to certain flows. This is done by either raising the priority of a flow or limiting thepriority of another flow. When using congestion-management tools, you try to raise the priority of a flow by queuing and servicing queues in different ways. The queue management tool used for congestion avoidance raises priority by dropping lower-priority flows before higher-priority flows. Policing and shaping provide priority to a flow by limiting the throughput of other flows. Link efficiency tools...
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