Overview

Three different models exist for implementing quality of service (QoS) on a network. The Best-Effort model was designed for best-effort, no-guarantee delivery of packets and is still the predominant model in the Internet today. The Integrated Services (IntServ) model was introduced to supplement the best-effort delivery by setting aside some bandwidth for applications that require bandwidth and delay guarantees. IntServ expects applications to signal their requirements to the network. The Differentiated Services (DiffServ) model was added to provide greater scalability in providing QoS to IP packets. The main difference between the IntServ and DiffServ models is that in DiffServ, the network recognizes packets (no signaling is needed) and provides the appropriate services to the packets. IP networks today can use all three models at the same time.

Objectives

Upon completing this lesson, you will be able to correctly match QoS actions to one or more models for implementing QoS on a network. This ability includes being able to meet these objectives:

■ Describe the types of models for providing QoS on a network

■ Describe the key features of the Best-Effort model for QoS

■ Describe the key features of IntServ for QoS

■ Describe the key features of DiffServ for QoS

QoS Models

The following three models exist for implementing QoS in a network:

■ Best-Effort: With the Best-Effort model, QoS is not applied to packets. If it is not important when or how packets arrive, the Best-Effort model is appropriate.

■ IntServ: IntServ can provide very high QoS to IP packets. Essentially, applications signal to the network that they will require special QoS for a period of time and that bandwidth is reserved. With IntServ, packet delivery is guaranteed. However, the use of IntServ can severely limit the scalability of a network.

■ DiffServ: DiffServ provides the greatest scalability and flexibility in implementing QoS in a network. Network devices recognize traffic classes and provide different levels of QoS to different traffic classes.

Best-Effort Model

Best-Effort Model

Internet initially based on a best-effort packet delivery service

The default mode for all traffic

No differentiation between types of traffic

Like using standard mail

Internet initially based on a best-effort packet delivery service

The default mode for all traffic

No differentiation between types of traffic

Like using standard mail

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