Cisco DQOS exam certification guide

Cisco Press

201 West 103rd Street

Indianapolis, IN 46290 USA

Cisco Press

IP Telephony Self-Study

Cisco DQOS

Exam Certification Guide

Wendell Odom, CCIE No. 1624

Michael J. Cavanaugh, CCIE No. 4516

DQOS.book Page i Wednesday, July 16, 2003 4:06 PM

ii

IP Telephony Self-Study

Cisco DQOS Exam Certification Guide

Wendell Odom and Michael J. Cavanaugh

Copyright © 2004 Cisco Systems, Inc.

Cisco Press logo is a trademark of Cisco Systems, Inc.

Published by:

Cisco Press

201 West 103rd Street

Indianapolis, IN 46290 USA

All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or

mechanical, including photocopying, recording, or by any information storage and retrieval system, without written

permission from the publisher, except for the inclusion of brief quotations in a review.

Printed in the United States of America 1 2 3 4 5 6 7 8 9 0

Library of Congress Cataloging-in-Publication Number: 2001097407

ISBN: 1-58720-058-9

First Printing July 2003

Warning and Disclaimer

This book is designed to provide information about quality of service (QoS) for the Cisco Catalyst switch platform.

Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is

implied.

The information is provided on an “as is” basis. The authors, Cisco Press, and Cisco Systems, Inc. shall have neither

liability nor responsibility to any person or entity with respect to any loss or damages arising from the information

contained in this book or from the use of the discs or programs that may accompany it.

The opinions expressed in this book belong to the author and are not necessarily those of Cisco Systems, Inc.

Trademark Acknowledgments

All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized.

Cisco Press or Cisco Systems, Inc. cannot attest to the accuracy of this information. Use of a term in this book should

not be regarded as affecting the validity of any trademark or service mark.

These materials have been reproduced by Pearson Technology Group with the permission of Cisco Systems Inc.

COPYRIGHT © 2003 CISCO SYSTEMS, INC. ALL RIGHTS RESERVED.

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DQOS.book Page ii Wednesday, July 16, 2003 4:06 PM

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Publisher John Wait

Editor-In-Chief John Kane

Cisco Representative Anthony Wolfenden

Cisco Press Program Manager Sonia Torres Chavez

Cisco Marketing Communications Scott Miller

Manager

Cisco Marketing Program Manager Edie Quiroz

Executive Editor Brett Bartow

Production Manager Patrick Kanouse

Development Editor Ginny Bess Munroe

Copy Editor Keith Cline

Technical Editors Frank Knox and Tim Szigeti

Team Coordinator Tammi Ross

Book Designer Gina Rexrode

Cover Designer Louisa Klucznik

Compositor Octal Publishing, Inc.

Indexer Larry Sweazy

Proofreader Missy Pluta

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About the Authors

Wendell Odom, CCIE No. 1624, is a senior instructor with Skyline Computer (www.skylinecomputer.com). Wendell

has worked in the networking arena for 20 years, working in pre- and post-sales technical consulting, teaching, and

course development. He has authored portions of over 12 courses, including topics such as IP routing, MPLS, Cisco

WAN switches, SNA protocols, and LAN troubleshooting. He is author of the bestselling Cisco Press title CCNA Exam

Certification Guide.

Michael J. Cavanaugh, CCIE No. 4516, has been in the networking industry for over 17 years. His employment with

such companies as General Electric, Cisco Systems, and Bellsouth Communication Systems has allowed him to stay at

the forefront of technology and hold leading edge certifications. His current focus is AVVID implementations, providing

convergance consulting, professional services, and technical support. Michael’s passion is learning the practical applica￾tions of new technologies and sharing knowledge with fellow engineers.

About the Technical Reviewers

Frank Knox, CCIE No. 3698 (Routing & Switching and SNA-IP), is currently the chief technology officer for

Skyline Computer Corporation. Frank also participates in the business as a consultant and instructor in the areas of

design, implementation, and customer training for all aspects of networking, including IP telephony. Frank has more

than 35 years of networking experience with IBM, GTE, and Skyline Computer. During that time, he has worked in field

service and support, product planning, education, and management. In addition, he has developed and taught several

courses for the University of Dallas (Telecommunications MBA program). Frank has a master’s degree in telecommuni￾cations from Pace University.

Tim Szigeti, CCIE No. 9794, is a member of the Enterprise Solutions Engineering design team at Cisco Systems. In

this role, he works closely with customers and engineering to develop advanced, scalable, and tested solutions for the

Cisco AVVID Network Infrastructure (CANI). Prior to this, he was performing technical marketing and product man￾agement within the Enterprise Management Business Unit, specializing in QoS Management.

Dedications

Wendell Odom: Mike Zanotto, or Mike Z as he’s known throughout California and the world, has had a significant

impact on my personal involvement with this book. Mike let me start our company’s efforts to teach DQOS classes back

in 2001—even when it didn’t look like the class would be that popular—just because it might turn into more. Well, it

turned out to be a great move for Skyline Computer, and for me. Mike’s willingness to take chances like that has had a

lot to do with Skyline’s success over the years. As my boss, he makes it possible for me to have time to write without

totally destroying all of my time for my family! As a friend, he helps keep me laughing, and not take the networking

world too seriously. Mike Z, thanks for helping make this book possible!

Michael J. Cavanaugh: I would like to dedicate this book to my lovely wife KC and beautiful daughter Caitlin for their

love and support through the years, but especially as I took my first steps in writing. I would like to thank Wendell

Odom for giving me the opportunity to co-author this book. It has been an exciting and challenging experience. I would

also like to thank all of the people at Cisco Press and the technical editors that made this book a reality.

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Acknowledgments

My uncle Eulie used to work in the meat market in the small town I grew up in. I loved hot dogs—but he’d never let me

see how they made them!! He always told me that if I liked them, then I really didn’t want to know how they were made!

This book has taken a while to complete, with several distractions from all directions. The path we all took to complete

this book was a little messy—like making hot dogs, I’m sure—and two individuals in particular made this book possible

in spite of the interruptions and diversions.

Michael Cavanaugh, my co-author, worked tirelessly to finish several key components of the book. His vast practical

skills have improved the book tremendously. Michael got to do some of the more challenging parts of the book, and

under duress—Michael, thanks so much for making the difference!

Ginny Bess, the development editor for this book, got the opportunity to jump into the mix mid-project. While many

people contribute to the success of any book, the development editor is the author’s main contact for submitting and

editing the content. When Gin came on board, we didn’t miss a beat, with book development running very smoothly.

When job responsibilities required a change in development editors mid-stream, we knew it was a risk, but Ginny came

through and did an excellent job.

Chris Cleveland started the book development and gave us guidance as needed. Chris’s primary focus is to make the

author’s life easier, and as always, he succeeded. Thanks for the usual stellar job!

Brett Bartow, executive editor for this project, happens to be an avid baseball fan, as am I. Brett’s job requires that he be

able to “hit major league curveballs”—for you non-baseball fans, that means he can hit a moving target with the best of

them. Once again, Brett, your steady hand throughout the entire writing and editing process helped make this project a

success. Thanks for staying on top of the positioning and business issues relating to the book.

Moreso than for most books, this book required some extra effort on the figures in the book. Amy Parker created several

new icons for this book, with these icons representing some relatively complex concepts. Amy came through for us,

taking my general comments and rough ideas, in some cases refining them, and in others coming up with whole new

(and much better) ways to represent the concepts. Thanks much!

Finally, the production side of the business does not get as much notice, because the author (me) who writes these acknowl￾edgements seldom works directly with them. Over the last few years, I’ve gotten to see more of their work, and believe me, I

really do have the easy part of the job. I deliver Word documents and Powerpoint (rough) drawings—and all production does

is somehow make this wonderfully polished book appear. Thanks for making me look good again, and again, and again!

As usual, the technical editors deserve most of the credit for making the content of this book robust and complete. For this

edition, Tim Szigeti and Frank Knox did the technical editing. Tim’s job requires that he help define and evangelize what

Cisco views as “best practices” for QoS deployments. His practical experience and ability to communicate well helped us

make this book a much more practical reference. Tim, thanks for your work and your patience in helping us resolve the occa￾sional difference between what’s on the exams and in the QoS courses, as compared with Cisco’s suggested best practices!

Frank Knox, dual CCIE and someone I personally credit with getting me interested in the training world 15 years ago,

also worked hard on the technical editing process. Frank’s no-nonsense approach to editing, with an occasional nonsen￾sical joke thrown in, both helped the manuscript improve, and kept me a little saner during my re-work of the chapters

based on his comments. Thanks to you both for making this book so much better!

Ultimately, Michael and I are most responsible for the contents of the book, so any errors you find are certainly our fault.

However, if you do think you found an error, the best way to get in touch to report the error is to go to www.ciscopress.com,

click on the “Contact Us” tab, and fill in the form. When it’s something that needs a look from the authors, the information

gets to us expediently. If it’s a problem that can be handled by the publisher, they can get to it even more quickly!

Finally, no section called acknowledgments could be complete without acknowledging a few others. My wife, Kris, regularly

takes on all the load for practical stuff at home, instead of the usual majority of the load, when a book project comes down to

the wire. This time around, we had three books on similar deadlines. As always, Kris, thanks for helping me when the timing

is tight! And ultimately, in this book effort and all else, I must acknowledge Jesus Christ, my friend, intercessor, and savior!

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Contents at a Glance

Foreword xvii

Introduction xviii

Chapter 1 QoS Overview 3

Chapter 2 QoS Tools and Architectures 83

Chapter 3 Classification and Marking 155

Chapter 4 Congestion Management 233

Chapter 5 Traffic Policing and Shaping 319

Chapter 6 Congestion Avoidance Through Drop Policies 425

Chapter 7 Link-Efficiency Tools 479

Chapter 8 Call Admission Control and QoS Signaling 541

Chapter 9 Management Tools and QoS Design 657

Chapter 10 LAN QoS 687

Appendix A Answers to the “Do I Know This Already?” Quizzes and Q&A Sections 763

Appendix B Topics on the CCIP QoS Exam 831

Index 883

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Table of Contents

Foreword xvii

Introduction xviii

Chapter 1 QoS Overview 3

“Do I Know This Already?” Quiz 3

QoS: Tuning Bandwidth, Delay, Jitter, and Loss Questions 4

Traffic Characteristics of Voice, Video, and Data Questions 5

Foundation Topics 6

QoS: Tuning Bandwidth, Delay, Jitter, and Loss 7

Bandwidth 9

The clock rate Command Versus the bandwidth Command 11

QoS Tools That Affect Bandwidth 11

Delay 13

Serialization Delay 14

Propagation Delay 16

Queuing Delay 18

Forwarding Delay 20

Shaping Delay 20

Network Delay 22

Delay Summary 23

QoS Tools That Affect Delay 24

Jitter 27

QoS Tools That Affect Jitter 28

Loss 29

QoS Tools That Affect Loss 29

Summary: QoS Characteristics: Bandwidth, Delay, Jitter, and Loss 32

Traffic Characteristics of Voice, Video, and Data 32

Voice Traffic Characteristics 33

Voice Basics 33

Voice Bandwidth Considerations 36

Voice Delay Considerations 39

Voice Jitter Considerations 48

Voice Loss Considerations 49

Video Traffic Characteristics 52

Video Basics 52

Video Bandwidth Considerations 54

Video Delay Considerations 55

Video Jitter Considerations 56

Video Loss Considerations 57

Comparing Voice and Video: Summary 57

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Data Traffic Characteristics 57

IP Data Basics 58

Data Bandwidth Considerations 63

Data Delay Considerations 64

Data Jitter Considerations 64

Data Loss Considerations 65

Comparing Voice, Video, and Data: Summary 66

Foundation Summary 67

Q&A 79

Chapter 2 QoS Tools and Architectures 83

“Do I Know This Already?” Quiz 83

QoS Tools Questions 84

Differentiated Services Questions 85

Integrated Services Questions 85

Foundation Topics 86

Introduction to IOS QoS Tools 86

Classification and Marking 86

Classification and Marking Tools 89

Queuing 90

Queuing Tools 91

Shaping and Policing 93

Shaping and Policing Tools 95

Congestion Avoidance 96

Congestion-Avoidance Tools 97

Link Efficiency 97

Link-Efficiency Tools: Summary 99

Call Admission Control and RSVP 100

CAC Tools 101

Management Tools 102

Summary 103

The Good-Old Common Sense QoS Model 104

GOCS Flow-Based QoS 105

GOCS Class-Based QoS 108

Classification and Marking at the Edge 109

The Differentiated Services QoS Model 114

DiffServ Specifications and Terminology 114

DiffServ Per-Hop Behaviors 119

The Class Selector PHB and DSCP Values 121

The Assured Forwarding PHB and DSCP Values 125

The Expedited Forwarding PHB and DSCP Values 128

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DiffServ Classifiers and Traffic Conditioners 129

The Integrated Services QoS Model 133

Foundation Summary 137

Q&A 152

Chapter 3 Classification and Marking 155

“Do I Know This Already?” Quiz Questions 155

Classification and Marking Concepts Questions 156

CAR, PBR, and CB Marking Questions 157

Foundation Topics 158

Classification and Marking Concepts 158

Classification 158

Marking 162

IP Header QoS Fields: Precedence and DSCP 163

LAN Class of Service (CoS) 166

Other Marking Fields 168

Summary of Marking Fields 168

Classification and Marking Design Choices 170

Classification and Marking Tools 175

Class-Based Marking (CB Marking) 175

Network-Based Application Recognition (NBAR) 185

CB Marking show Commands 189

CB Marking Summary 193

Committed Access Rate (CAR) 193

CAR Marking Summary 200

Policy-Based Routing (PBR) 201

PBR Marking Summary 207

VoIP Dial Peer 207

VoIP Dial-Peer Summary 214

Summary of Classification and Marking QoS Features 214

Foundation Summary 217

Q&A 229

Chapter 4 Congestion Management 233

“Do I Know This Already?” Quiz 233

Queuing Concepts Questions 234

WFQ and IP RTP Priority Questions 234

CBWFQ and LLQ Questions 235

Comparing Queuing Options Questions 235

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Foundation Topics 236

Queuing Concepts 236

Output Queues, TX Rings, and TX Queues 239

Queuing on Interfaces Versus Subinterfaces and Virtual Circuits (VCs) 245

Summary of Queuing Concepts 248

Queuing Tools 248

FIFO Queuing 249

Priority Queuing 251

Custom Queuing 254

Weighted Fair Queuing (WFQ) 257

WFQ Classification 258

WFQ Scheduler: The Net Effect 259

WFQ Scheduling: The Process 260

WFQ Drop Policy, Number of Queues, and Queue Lengths 264

WFQ Configuration 266

WFQ Summary 271

Class-Based WFQ (CBWFQ) 272

CBWFQ Configuration 275

CBWFQ Summary 287

Low Latency Queuing (LLQ) 288

LLQ Configuration 290

LLQ with More Than One Priority Queue 295

IP RTP Priority 296

IP RTP Priority Configuration 297

Summary of Queuing Tool Features 299

Foundation Summary 301

Q&A 313

Conceptual Questions 313

Priority Queuing and Custom Queuing 313

WFQ 314

CBWFQ, LLQ, IP RTP Priority 314

Comparing Queuing Tool Options 316

Chapter 5 Traffic Policing and Shaping 319

“Do I Know This Already?” Quiz 319

Shaping and Policing Concepts Questions 320

Policing with CAR and CB Policer Questions 320

Shaping with FRTS, GTS, DTS, and CB Shaping 321

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Foundation Topics 322

Traffic-Policing and Traffic-Shaping Concepts 322

When and Where to Use Shaping and Policing 323

Policing—When and Where? 324

Traffic Shaping—When and Where? 327

How Shaping Works 330

Traffic Shaping, Excess Burst, and Token Buckets 335

Traffic-Shaping Adaption 337

Where to Shape: Interfaces, Subinterfaces, and VCs 338

Queuing and Traffic Shaping 340

How Policing Works 343

CAR Internals 343

CB Policing Internals 348

Policing, but Not Discarding 350

Traffic-Shaping Tools 351

Generic Traffic-Shaping Configuration 351

Class-Based Shaping Configuration 357

Distributed Traffic Shaping (DTS) Configuration 369

Frame Relay Traffic Shaping (FRTS) Configuration 370

Traffic-Policing Tools 388

Class-Based Policing Configuration 390

Committed Access Rate (CAR) Configuration 398

Foundation Summary 405

Q&A 421

Shaping and Policing Concepts 421

Traffic Shaping 422

Traffic-Policing Tools 423

Chapter 6 Congestion Avoidance Through Drop Policies 425

“Do I Know This Already?” Quiz 425

Congestion-Avoidance Concepts and RED Questions 426

WRED Questions 426

FRED Questions 427

Foundation Topics 428

Congestion-Avoidance Concepts and Random Early Detection (RED) 428

TCP and UDP Reactions to Packet Loss 428

Tail Drop, Global Synchronization, and TCP Starvation 432

Random Early Detection (RED) 434

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Weighted RED (WRED) 437

How WRED Weights Packets 437

WRED and Queuing 441

WRED Configuration 443

WRED Summary 455

Flow-Based WRED (FRED) 456

FRED Configuration 459

Foundation Summary 466

Q&A 475

Congestion-Avoidance Concepts and Random Early Detection (RED) 475

Weighted RED (WRED) 476

Flow-Based WRED (FRED) 476

Chapter 7 Link-Efficiency Tools 479

“Do I Know This Already?” Quiz 480

Compression Questions 480

Link Fragmentation and Interleave Questions 481

Foundation Topics 482

Payload and Header Compression 482

Payload Compression 484

Header Compression 485

Payload Compression Configuration 486

TCP and RTP Header Compression Configuration 490

Link Fragmentation and Interleaving 494

Multilink PPP LFI 497

Maximum Serialization Delay and Optimum Fragment Sizes 498

Frame Relay LFI Using FRF.12 499

Choosing Fragment Sizes for Frame Relay 503

Fragmentation with More Than One VC on a Single Access Link 504

Multilink PPP Interleaving Configuration 506

Frame Relay Fragmentation Configuration 515

FRF.11-C and FRF.12 Comparison 525

Foundation Summary 528

Q&A 536

Compression Tools 536

LFI Tools 537

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Chapter 8 Call Admission Control and QoS Signaling 541

“Do I Know This Already?” Quiz 542

Foundation Topics 544

Call Admission Control Overview 544

Call Rerouting Alternatives 545

Bandwidth Engineering 546

CAC Mechanisms 552

CAC Mechanism Evaluation Criteria 553

Local Voice CAC 554

Physical DS0 Limitation 554

Max-Connections 556

Voice over Frame Relay—Voice Bandwidth 563

Trunk Conditioning 566

Local Voice Busyout 569

Measurement-Based Voice CAC 571

Service Assurance Agents 572

SAA Probes Versus Pings 572

SAA Service 572

Calculated Planning Impairment Factor 573

Advanced Voice Busyout 573

PSTN Fallback 575

SAA Probes Used for PSTN Fallback 576

IP Destination Caching 576

SAA Probe Format 578

PSTN Fallback Configuration 578

PSTN Fallback Scalability 581

PSTN Fallback Summary 582

Resource-Based CAC 584

Resource Availability Indication 585

Gateway Calculation of Resources 585

RAI in Service Provider Networks 586

RAI in Enterprise Networks 588

RAI Operation 589

RAI Configuration 589

RAI Platform Support 590

Cisco CallManager Resource-Based CAC 591

Location-Based CAC Operation 591

Locations and Regions 592

Calculation of Resources 594

Automatic Alternate Routing 595

Location-Based CAC Summary 595

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Gatekeeper Zone Bandwidth 596

Gatekeeper Zone Bandwidth Operation 596

Single-Zone Topology 596

Multizone Topology 597

Zone-per-Gateway Design 601

Gatekeeper in CallManager Networks 601

Zone Bandwidth Calculation 602

Zone Bandwidth Configuration 604

Gatekeeper Zone Bandwidth Summary 605

Integrated Services / Resource Reservation Protocol 606

RSVP Levels of Service 607

RSVP Operation 608

RSVP/H.323 Synchronization 611

RSVP Synchronization Configuration 612

Classification for Voice Packets into LLQ 615

Bandwidth per Codec 616

Subnet Bandwidth Management 617

RSVP Configuration 618

Monitoring and Troubleshooting RSVP 621

RSVP CAC Summary 624

Foundation Summary 626

Q&A 654

Call Admission Control Concepts 654

Local-Based CAC 654

Measurement-Based CAC 655

Resources-Based CAC 655

Chapter 9 Management Tools and QoS Design 657

“Do I Know This Already?” Quiz 657

QoS Management Tools Questions 658

QoS Design Questions 659

Foundation Topics 660

QoS Management Tools 660

QoS Device Manager 660

QoS Policy Manager 662

Service Assurance Agent 664

Internetwork Performance Monitor 666

Service Management Solution 666

QoS Management Tool Summary 668

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QoS Design for the Cisco QoS Exams 668

Four-Step QoS Design Process 669

Step 1: Determine Customer Priorities/QoS Policy 670

Step 2: Characterize the Network 670

Step 3: Implement the Policy 671

Step 4: Monitor the Network 672

QoS Design Guidelines for Voice and Video 673

Voice and Video: Bandwidth, Delay, Jitter, and Loss Requirements 673

Voice and Video QoS Design Recommendations 676

Foundation Summary 679

Q&A 684

QoS Management 684

QoS Design 685

Chapter 10 LAN QoS 687

“Do I Know This Already?” Quiz 687

Foundation Topics 690

The Need for QoS on the LAN 690

Buffer Overflow (Overrun) 690

Marking and Classification 691

Layer 3-to-Layer 2 Classification Mapping 693

Layer 2 Queues 694

Drop Thresholds 695

Trust Boundries 696

Cisco Catalyst Switch QoS Features 698

Catalyst 6500 QoS Features 698

Supervisor and Switching Engine 698

Policy Feature Card 701

Ethernet Interfaces 702

QoS Flow on the Catalyst 6500 706

Ingress Queue Scheduling 707

Layer 2 Switching Engine QoS Frame Flow 709

Layer 3 Switching Engine QoS Packet Flow 710

Egress Queue Scheduling 710

Catalyst 6500 QoS Summary 713

Cisco Catalyst 4500/4000 QoS Features 717

Supervisor Engine I and II 718

Supervisor Engine III and IV 719

Cisco Catalyst 3550 QoS Features 721

Cisco Catalyst 3524 QoS Features 722

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