C HAPTER
2
End-to-End QoS: Quality of
Service at Layer 3 and Layer 2
Chapter 1, “Quality of Service: An Overview,” introduced several of the fundamental
concepts of quality of service (QoS), various key RFCs, and explained various parts of the
differentiated services (DiffServ) architecture. This chapter builds upon Chapter 1 by
continuing to explore some DiffServ components and looking at mechanisms for traffic
conditioning, link efficiency, and classification at Layer 3. This chapter also introduces the
concept of Layer 2 packet marking for QoS and explains how Layer 2 markings relate to
Layer 3 markings to facilitate end-to-end QoS. Although this chapter doesn’t focus specif-
ically on QoS for IP telephony applications, you will find examples of how Layer 2 QoS is
used to allow voice traffic to traverse a switched infrastructure with limited delay and jitter.
This chapter also looks at various traffic-conditioning components of QoS.
This chapter primarily focuses on QoS from a Cisco IOS router perspective. In addition, all
the examples of this chapter were demonstrated on a Cisco IOS router. The last two sections
of this chapter introduce QoS on the Catalyst platforms.
QoS Components
As discussed in Chapter 1, QoS is comprised of various components. This chapter discusses
the following QoS components in detail:
• Congestion Management
• Congestion Avoidance
• Traffic Conditioning
• Link Efficiency
Each QoS component plays an important role in building an overall QoS strategy for your
network, and each component offers unique characteristics that add value to your strategy.
In addition to discussing the various components, this chapter introduces you to some Cisco
implementations of these components. After discussing the concepts in general terms, this
chapter provides configuration examples and details how to verify your configurations
using show commands.
Simply defined, congestion exists when an interface is offered more traffic for transmission than
it is capable of transmitting. Congestion is usual in several common network design scenarios:
..................Content has been hidden....................
You can't read the all page of ebook, please click here login for view all page.