Foundation Summary 67

Foundation Summary

The “Foundation Summary” is a collection of tables and figures that provide a convenient review of many key concepts in this chapter. For those of you already comfortable with the topics in this chapter, this summary could help you recall a few details. For those of you who just read this chapter, this review will help solidify some key facts. For any of you doing your final prep before the exam, these tables and figures will be a convenient way to review the day before the exam.

Table 1-29 outlines some of the behaviors seen when no QoS is applied in a network.

Table 1-29 Traffic Behavior with No QoS

As shown in Figure 1-36, with compression, if a ratio of 2:1 is achieved, the 80-kbps flow will only require 40 kbps in order to be sent across the link—effectively doubling the bandwidth capacity of the link.

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Figure 1-40 depicts LFI operation.

Figure 1-40 Link Fragmentation and Interleaving

Legend: Px Fy Means Packet Number x, Fragment Number y

Although adding more bandwidth always helps, the tools summarized in Table 1-31 do help to improve the effects of delay in a network.

Table 1-31 QoS Tools That Affect Delay

Figure 1-41 shows the jitter experienced by three packets as part of a voice call between phones at extension 301 and 201.

Foundation Summary 71

Figure 1-41 Jitter Example

Server 1

301

The same set of tools that affect delay also affect jitter; Table 1-32 lists some of these QoS tools.

Table 1-32 QoS Tools That Affect Jitter

With a longer maximum queue size, likelihood of loss decreases. However, queuing delay increases, as shown in Figure 1-42.

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Table 1-38 Delay Components, Variable and Fixed (Continued)

Figure 1-46 shows an example of jitter for packets 3 and 4.

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Two factors affect the delay requirements of a data application. Table 1-41 lists these requirements.

Table 1-41 Factors to Consider for Data Delay

Table 1-42 summarizes the QoS requirements of data, in comparison to voice and video.

Table 1-42 Comparing Voice, Video, and Data QoS Requirements

Q&A 79

Q&A

As mentioned in the Introduction, you have two choices for review questions. The questions that follow next give you a more difficult challenge than the exam itself by using an open-ended question format. By reviewing now with this more difficult question format, you can exercise your memory better, and prove your conceptual and factual knowledge of this chapter. You can find the answers to these questions in Appendix A.

The second option for practice questions is to use the CD-ROM included with this book. It includes a testing engine and more than 200 multiple-choice questions. You should use this CD-ROM nearer to the end of your preparation, for practice with the actual exam format. You can even customize the CD-ROM exam to include, or not include, the topics that are only on the CCIP QoS.

1List the four traffic characteristics that QoS tools can affect.

2Describe some of the characteristics of voice traffic when no QoS is applied in a network.

3Describe some of the characteristics of video traffic when no QoS is applied in a network.

4Describe some of the characteristics of data traffic when no QoS is applied in a network.

5Interpret the meaning of the phrase, “QoS is both ‘managed fairness,’ and at the same time ‘managed unfairness’.”

6Define bandwidth. Compare and contrast bandwidth concepts over point-to-point links versus Frame Relay.

7Compare and contrast bandwidth and clock rate in relation to usage for QoS.

8List the QoS tool types that affect bandwidth, and give a brief explanation of why each tool can affect bandwidth.

9Define delay, compare/contrast one-way and round-trip delay, and characterize the types of packets for which one-way delay is important.

10List the categories of delay that could be experienced by all three types of traffic: data, voice, and video.

11Define, compare, and contrast serialization and propagation delay.

12Define network delay.

13List the QoS tool types that affect delay and give a brief explanation of why each tool can affect delay.

14Define jitter. Give an example that shows a packet without jitter, followed by a packet with jitter.

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15List the QoS tool types that affect jitter and give a brief explanation of why each tool can affect jitter.

16Define packet loss and describe the primary reason for loss for which QoS tools can help.

17List the QoS tool types that affect loss and give a brief explanation of why each tool can affect loss.

18Describe the contents of an IP packet carrying the payload for a G.729 VoIP call.

19Describe the amount of bandwidth required for G.711 and G.729 VoIP calls, ignoring data-link header/trailer overhead.

20List the delay components that voice calls experience, but which data-only flows do not experience.

21Define the meaning of the term “packetization delay” in relation to a voice call.

22List the different one-way delay budgets as suggested by Cisco and the ITU.

23Define the term “codec delay” and discuss the two components when using a G.729 codec.

24Describe the affects of a single lost packet versus two consecutive lost packets, for a G.729 voice call.

25Describe a typical video payload flow in terms of packet sizes and packet rates.

26Discuss the delay requirements of video traffic.

27List the basic differences between TCP and UDP traffic.

28Contrast the QoS characteristics needed by interactive data applications, as compared to the QoS needs of voice payload flows.

This chapter covers the following exam topics specific to the DQOS and QoS exams:

DQOS Exam Topics

•Correctly describe the QoS framework.

•Describe the differences between integrated services and differentiated services.

QoS Exam Objectives

•Describe the Integrated Services model

•List the key benefits and drawbacks of the IntServ model

•Describe the Differentiated Services model

•List the key benefits of the DiffServ model compared to the IntServ 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

•Describe the interoperability between DSCP-based and IP-precedence based devices in a network