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DQOS Exam Certification Guide - Cisco press.pdf
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C H A P T E R 2

QoS Tools and Architectures

To build a house, you need tools, you need materials, you need labor, and you need architectural plans. To build a network using quality of service (QoS), you need tools and you need an architecture. This chapter lists the various IOS QoS tools and explains the two predominant QoS architectures: integrated services (IntServ) and differentiated services (DiffServ).

Chapter 1, “QoS Overview,” covered various types of QoS tools. Now this chapter begins with a review of the types of tools and lists each of the IOS QoS tools in each category. This chapter also introduces the most important acronyms for the QoS exams. All the terms, and the tools behind the terms, get further treatment in later chapters of the book.

As a tool for learning, the second section of this chapter explains something called the Good-Old Common Sense model for QoS. This imaginary QoS model just explains some things about QoS that many people have heard about before. However, taking a few minutes to think about these concepts, and why they make sense, is useful before looking at the two formalized QoS models—namely DiffServ and IntServ.

This chapter then examines the DiffServ architecture in detail. DiffServ attempts to provide Internet-scale QoS, which is a lofty goal indeed! DiffServ uses a class-based approach to differentiate between packets, which scales somewhat better than its predecessor, IntServ. Whether DiffServ succeeds in this goal remains to be seen; however, many of the concepts can be helpful with any QoS implementation.

Finally, the chapter ends with a short discussion on IntServ, which uses the Resource Reservation Protocol (RSVP) to reserve bandwidth for individual flows in the network.

This chapter concludes the introductory materials in this book; the remainder of this book delves into the details of the various QoS tools.

“Do I Know This Already?” Quiz

The purpose of the “Do I Know This Already?” quiz is to help you decide whether you really need to read the entire chapter. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now.

The 12-question quiz, derived from the major sections in the “Foundation Topics” section of this chapter, helps you determine how to spend your limited study time.

84 Chapter 2: QoS Tools and Architectures

Table 2-1 outlines the major topics discussed in this chapter and the “Do I Know This Already?” quiz questions that correspond to those topics.

Table 2-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping


Foundation Topics Section Covering These












QoS Tools

1 to 4







Differentiated Services

5 to 8







Integrated Services

9 to 12






All questions


1 to 12






CAUTION The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you do not know the answer to a question or are only partially sure of the answer, mark this question wrong for purposes of the self-assessment. Giving yourself credit for an answer you correctly guess skews your self-assessment results and might provide you with a false sense of security.

You can find the answers to the “Do I Know This Already?” quiz in Appendix A, “Answers to the ‘Do I Know This Already?’ Quizzes and Q&A Sections.” The suggested choices for your next step are as follows:

10 or less overall score—Read the entire chapter. This includes the “Foundation Topics,” the “Foundation Summary,” and the “Q&A” sections.

11 or 12 overall score—If you want more review on these topics, skip to the “Foundation Summary” section and then go to the “Q&A” section. Otherwise, proceed to the next chapter.

QoS Tools Questions

1List four queuing tools, including the full names and popular acronyms.

2List four link-efficiency tools, including the full names and popular acronyms.

3Which of the following tools can be used for classification and marking? CAR, CB marking, PQ, CB shaping, QDM, WFQ, WRED, FRTS, LLQ, GTS, RAI, FRF, RSVP, SAA, MLPPP LFI, AVBO, CQ, NBAR, QPM, CAR, FRED, QPPB, cRTP

4Which of the following tools can be used for policing? CAR, CB marking, PQ, CB shaping, QDM, WFQ, WRED, FRTS, LLQ, GTS, RAI, FRF, RSVP, SAA, MLPPP LFI, AVBO, CQ, NBAR, QPM, CAR, FRED, QPPB, cRTP

“Do I Know This Already?” Quiz 85

Differentiated Services Questions

5Define the DiffServ term “DSCP,” including what the acronym stands for.

6Define the DiffServ term “PHB,” including what the acronym stands for.

7Compare and contrast the terms “shaper,” “meter,” and “dropper,” according to DiffServ specifications. Suggest typical points in the network where each is used.

8Compare and contrast the contents of the IP ToS byte before and after the advent of DiffServ.

Integrated Services Questions

9Imagine an enterprise network, connected to an Internet service provider (ISP), that is connected to a second ISP, which is then connected to another enterprise network. The second ISP does not support IntServ directly. Discuss the two options that allow the other three networks to support IntServ for flows that pass through the nonsupporting ISP.

10Compare and contrast DiffServ and IntServ in terms of using classes, flows, and scalability.

11Describe the two options available to a router to perform IntServ admission control.

12What is the QoS framework, and what does it define?