About the QOS 642-642 Exam Certification Guide
This section provides a brief insight into the contents of the book and the major goals, as well as some of the book features that you will encounter when using this book.
Goals of This Book
Unquestionably, the primary goal for this book is to help you pass the QOS certification exam. However, the means by which that goal is accomplished follows the Cisco Press Exam Certification Guide philosophy, which makes a statement about helping a reader pass the test through a deeper understanding of the material, as opposed to simply helping the reader memorize the answers to multiple-choice questions.
To accomplish this goal, the book's main chapters cover all the topics on the QOS exam, plus an occasional mention of topics outside the scope of the exam just to make a key point. The depth of the conceptual coverage exceeds the depth of coverage in the QOS course. By doing so, you should be able to pass the exam with greater confidence.
A secondary goal for this book is to help you prepare for the CCIE Routing/Switching and CCIE Voice exams. Although this goal wasn't actually intended when we wrote the first edition of this book, it turns out that a lot of people found the book useful for CCIE preparation as well. However, this second edition actually covers a narrower range of topics. Because CCIE covers a broad range of QoS topics, we kept some materials from earlier editions of the book and placed them in appendixes on the CD-ROM so that people working toward CCIE can still have the materials available.
The third goal is not so obvious. While written to help you pass the exams, it is our hope that this book will also be useful to anyone who needs to deploy QoS tools using Cisco gear. We hope that if you take the exam, you will keep this book as a desk reference, and for those of you who don't take the exam, we hope you find this book a useful tool for delving into the details and really understanding QoS.
After teaching the DQOS course for the last couple of years, and after hearing students continually ask where they could read more on QoS topics, it became apparent that there were few good options available. This book fills that gap and provides a comprehensive reference for Cisco QoS.
Book Organization
This book contains 10 core chapters with titles that are comparable to the major headings listed in the QOS exam topics. For QOS exam candidates, you can simply dive into Chapter 1 and read through Chapter 10.
Chapters 13 cover most of the core background information needed to understand the different classes of Cisco QoS tools.
Chapters 48 each cover a different major type of QoS tool, covering the concepts, as well as the configuration of the tools.
Chapter 9 specifically addresses QoS issues on LAN switches to a depth and breadth appropriate to the exam.
Finally, Chapter 10 covers information about QoS best practices as described in the QoS course materials. As always, make sure you check www.cisco.com for the latest news about any future changes to the exam.
Appendix A provides the answers to the "Do I Know This Already?" Quizzes and Q&A sections found in Chapters 110.
Additionally, you can find Appendix B "Additional QoS Reference Materials ," Appendix C, "Voice Call Admission Control Reference" and Appendix D, "LAN QoS Reference" on the CD-ROM accompanying this book. These CD-only appendixes are designed to supplement what you definitely need to know for the QOS exam with some topic area coverage that you should know as a CCIP candidate.
Following is a description of each chapter's coverage:
Chapter 1, "QoS Overview" QoS affects the characteristics of network traffic. To understand the QoS concepts and configurations discussed in other chapters, you must know what can be manipulated namely, bandwidth, delay, jitter, and packet loss. Also, different types of traffic have different needs for bandwidth, delay, jitter and loss. Chapter 1 defines QoS terms, explains the concepts relating to bandwidth, delay, jitter, and packet loss, and identifies the traffic characteristcs of data, voice, and video traffic. Chapter 2, "QoS Tools and Architectures" Cisco provides a large number of QoS tools inside the router IOS. One of the biggest challenges when preparing for either exam is remembering all the tools and keeping track of which tools provide what features. Chapter 2 begins by listing and describing the classes of tools, and then also listing the tools themselves. The remaining chapters delve into more depth on each particular class of tool. QoS tools typically either follow one of two QoS architectural philosophies. The two archtectures are called Differentiated Services and Integrated Services. The second part of this chapter explains the two architectures. Chapter 3, "MQC, QPM, and AutoQoS" Many of the best QoS tools in IOS today use a set of CLI commands called the Modular QoS CLI, or MQC. This chapter begins by explaining MQC and showing how MQC commands can be used to configure QOS. The other major topic in this chapter is AutoQoS, which automatically configures QoS features according to the Cisco best practices for QoS in a network with VoIP traffic. Along the way, a few related, minor topics are covered, such as QPM. Chapter 4, "Classification and Marking" Classification and Marking defines how a networking device can identify a particular packet and change some bits in the frame or packet header. The changed bits "mark" the packet, so other QoS tools can react to the marked field. This chapter covers the concepts, as well as five different classification and marking tools. Chapter 5, "Congestion Management" Queuing tools on routers manage packets while they are waiting to exit an interface. This chapter discusses the general concepts of queuing in Cisco routers, and then covers the concepts and configuration behind a large variety of queuing tools. The Cisco DQOS exam topics refer to Queuing as "Congestion Management." Chapter 6, "Traffic Shaping and Policing" Policing tools discard traffic that exceeds a particular rate. Shaping tools delay traffic so that, over time, the traffic rate does not exceed a particular rate. Both classes of tools use a concept of measuring the rate of sending or receiving bits. This chapter covers the general concepts of policing and shaping in Cisco routers, followed by the detailed concepts and configuration for two policing tools and four shaping tools. Chapter 7, "Congestion Avoidance Through Drop Policies" Interestingly, statistics show that the biggest reason that packets are lost in networks is because a queue fills, leaving no room to hold another packet, forcing the device to discard the packet. Congestion Avoidance tools monitor queue depths, discarding some packets before the queue fills. The early discards cause the computers that sent the dropped packets to slow down the rate of sending packets, abating the congestion. As usual, this chapter covers the concepts and then the configuration behind two congestion avoidance tools. Chapter 8, "Link Efficiency Tools" Link Efficiency tools deal with how to best use the bandwidth on a link between two routers. Compression, which is one class of link efficiency tool, reduces the required bandwidth. Fragmentation tools reduce delay for small, delay-sensitive packets by breaking large packets into smaller packets. The smaller delay-sensitive packets can be sent before the fragments of the original larger packet. This chapter covers the base concepts as well as the configuration details. Chapter 9, "LAN QoS" The QoS exam covers some specific tools for QoS on Cisco LAN switches. These topics are collected into a single chapter, with examples using 2950 Series switches. Chapter 10, "Cisco QoS Best Practices" The Cisco QoS course covers a set of recommendations for QoS in the Enterprise, as well as for service providers. This chapter covers those details. Appendix A, "Answers to the 'Do I Know This Already?' Quizzes and Q&A Sections" This appendix lists the questions covered at the beginning and end of each chapter, as well as their answers. Appendix B, "Additional QoS Reference Materials" (found on the book's accompanying CD-ROM) This appendix contains material from earlier editions of this book. A few topics might be useful as background information for your preparation for the exam, but the main purpose of the appendix is to list coverage of topics that could be on the CCIE exams. (These topics were not updated for this edition of the book and are available for reference with that caveat in mind.) Appendix C, "Voice Call Admission Control Reference," (found on the book's accompanying CD-ROM) This appendix is a reprint of the DQOS Exam Certification Guide's chapter on Voice Call Admission Control. Voice CAC is no longer on the QoS exam; it is included on the CD-ROM for reference for anyone interested in Voice CAC. (These topics were not updated for this edition of the book and are available for reference with that caveat in mind.) Appendix D, "LAN QoS Reference" (found on the book's accompanying CD-ROM) This appendix is a reprint of the DQOS Exam Certification Guide's chapter on LAN QoS. The current QoS exam covers different topics on LAN QoS, with specific focus on the QoS commands on the 2950 Series switches. This appendix contains a broader coverage of LAN QoS, and some samples and comparisons of QoS on different Cisco switches. (These topics were not updated for this edition of the book and are available for reference with that caveat in mind.)
Book Features
The core chapters of this book have several features that help you make the best use of your time:
"Do I Know This Already?" Quizes Each chapter begins with a quiz that helps you determine the amount of time you need to spend studying that chapter. If you follow the directions at the beginning of the chapter, the "Do I Know This Already?" quiz directs you to study all or particular parts of the chapter. Foundation Topics These are the core sections of each chapter. They explain the protocols, concepts, and configuration for the topics in that chapter. Foundation Summary
Near the end of each chapter, a summary collects the most important tables and figures from the chapter. The "Foundation Summary" section is designed to help you review the key concepts in the chapter if you scored well on the "Do I Know This Already?" quiz. This section is also an excellent tool for last-minute reviews before you take the exam. Q&A Each chapter ends with a Q&A section that forces you to exercise your recall of the facts and processes described in the chapter's foundation topics. The questions are generally harder than the actual exam, partly because the questions are in "short answer" format, instead of multiple choice format. These questions are a great way to increase the accuracy of your recollection of the facts and to practice for taking the exam. Examples Located inside the Foundation Topics of most chapters, the text includes screen captures from lab scenarios that show how each tool works. The examples include a topology, the configuration, and show command output that matches the examples. CD-based practice exam The companion CD contains multiple-choice questions and a testing engine. As part of your final preparation, you should practice with these questions to help you get used to the exam-taking process, as well as help refine and prove your knowledge of the exam topics.
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