Introduction to Network Simulator NS2

Teerawat Issariyakul • Ekram Hossain

Introduction to NetworkSimulator NS2

Second Edition

123

Teerawat IssariyakulTOT Public Company Limited89/2 Moo 3Chaengwattana Rd.Thungsonghong, LaksiBangkok 10210 Thailanditeerawat@hotmail.comns2ultimate.com

Ekram HossainDepartment of Electricaland Computer EngineeringUniversity of Manitoba75A Chancellor’s Circle 15Winnipeg, MB R3T 5V6Canadaekram@ee.umanitoba.ca

ISBN 978-1-4614-1405-6 e-ISBN 978-1-4614-1406-3DOI 10.1007/978-1-4614-1406-3Springer New York Dordrecht Heidelberg London

Library of Congress Control Number: 2011940220

© Springer Science+Business Media, LLC 2012All rights reserved. This work may not be translated or copied in whole or in part without the writtenpermission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York,NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use inconnection with any form of information storage and retrieval, electronic adaptation, computer software,or by similar or dissimilar methodology now known or hereafter developed is forbidden.The use in this publication of trade names, trademarks, service marks, and similar terms, even if they arenot identified as such, is not to be taken as an expression of opinion as to whether or not they are subjectto proprietary rights.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

To our families

Preface

Motivation for Writing This Book

First of all, we would like to thank you for your interest in this book. This book wasmotivated by our frustration when we were graduate students. We were pushed towork with NS2, when we did not know what to do. We looked over the Internet, but,at the time, there were very little material on the Internet. We posted our questionon every mailing list, every online forums we can think of. We did not find most ofwhat we were looking for. We spent days and nights on many operating systems justto make NS2 run on one of the systems we have. We spent an endless amount oftime, trying to understand the way NS2 moves a packet from one node to another.We did not succeed. So we were running out of time we pushed out and submittedour project/thesis as it was. Our program was as good as it was necessary to closethe project. We were not satisfied with our knowledge about NS2.

After the graduation, we revisited NS2 and tried to understand it more. Bitsby bits, we began to understand how NS2 does a certain thing, but perhaps moreimportantly why NS2 does so. From our experience, it takes months, if not years, totruly understand NS2.

We would not be surprised if our story above sounds particularly familiar to you.In fact, we expected you to experience a part, if not all, of our unpleasant experience.We wrote this book to ease your pain caused by NS2. We hope that this book canreduce your NS2 learning curve from years to months, or from months to weeks.

About NS2

NS2 is an open-source event-driven simulator designed specifically for researchin computer communication networks. Since its inception in 1989, NS2 hascontinuously gained tremendous interest from industry, academia, and government.Having been under constant investigation and enhancement for years, NS2 nowcontains modules for numerous network components such as routing, transportlayer protocol, and application. To investigate network performance, researchers can

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simply use an easy-to-use scripting language to configure a network, and observeresults generated by NS2. Undoubtedly, NS2 has become the most widely used opensource network simulator, and one of the most widely used network simulators.

Unfortunately, most research needs simulation modules which are beyond thescope of the built-in NS2 modules. Incorporating these modules into NS2 requiresprofound understanding of NS2 architecture. Currently, most NS2 beginners relyon online tutorials. Most of the available information mainly explains how toconfigure a network and collect results, but does not include sufficient informationfor building additional modules in NS2. Despite its details about NS2 modules, theformal documentation of NS2 is mainly written as a reference book, and does notprovide much information for beginners. The lack of guidelines for extending NS2is perhaps the greatest obstacle, which discourages numerous researchers from usingNS2. At the time of this writing, there is no official guide book which can help thebeginners understand the architecture of NS2 in depth.

About This Book

This book is designed to be an NS2 primer. It provides information required toinstall NS2, run simple examples, modify the existing NS2 modules, and create aswell as incorporate new modules into NS2. To this end, the details of several built-inNS2 modules are explained in a comprehensive manner.

NS2 by itself contains numerous modules. As time elapses, researchers keepdeveloping new NS2 modules. This book does not include the details of all NS2modules, but does so for selected modules necessary to understand the basics ofNS2. We believe that once the basics of NS2 are grasped, the readers can gothrough other documentations, and readily understand the details of other NS2components. The details of Network AniMator (NAM) and Xgraph are also omittedhere. We understand that these two tools are nice to have and could greatly facilitatesimulation and analysis of computer networks. However, we believe that they arenot essential to the understanding of the NS2 concept, and their information arewidely available through most of the online tutorials.

This textbook can be used by researchers who need to use NS2 for communica-tion network performance evaluation based on simulation. Also, it can be used asa reference textbook for laboratory works for a senior undergraduate level courseor a graduate level course on telecommunication networks offered in Electricaland Computer Engineering and Computer Science Programs. Potential coursesinclude “Network Simulation and Modeling,” “Computer Networks,” “Data Com-munications,” “Wireless Communications and Networking,” and “Special Topics onTelecommunications.”

Preface ix

Book Summary

This book starts off with an introduction to network simulation in Chap. 1. Webriefly discuss about computer networks and the layering concept. Then wegive board statements on system analysis approaches. As one of the two mainapproaches, simulation can be carried out in time-driven and event-driven modes.The latter is the one NS2 was developed.

Chapter 2 provides an overview of Network Simulator 2 (NS2). Shown in thischapter are the two-language NS2 architecture, NS2 directory, and the conventionsused in this book, and NS2 installation guidelines for UNIX and Windows systems.We also present a three-step simulation formulation as well as a simple example ofNS2 simulation. Finally, we demonstrate how to use the make utility to incorporatenew modules into NS2.

Chapter 3 explains the details of the NS2 two language structure, whichconsists of the following six main CCC classes: Tcl, Instvar, TclObject,TclClass, TclCommand, and EmbeddedTcl. Chapters 4 and 5 present thevery main simulation concept of NS2. While Chap. 4 explains implementation ofevent-driven simulation in NS2, Chap. 5 focuses on network objects as well aspacket forwarding mechanism.

Chapters 6–11 present the following six most widely used NS2 modules. First,nodes (Chap. 6) act as routers and computer hosts. Second, links, particularlySimpleLink objects (Chap. 7), deliver packets from one network object toanother. They model packet transmission time as well as packet buffering. Third,packets (Chap. 8) contain necessary information in its header. Fourth, agents(Chaps. 9–10) are responsible for generating packets. NS2 has two main transport-layer agents: TCP and UDP agents. Finally, applications (Chap. 11) model the userdemand for data transmission.

Up to Chap. 11, the book focuses mainly on wired networks. Chapter 12demonstrates how NS2 implements Wireless Mobile Ad Hoc Networks. Discussionof packet forwarding via wireless links and node mobility is given in this chapter.

After discussing all the NS components, Chap. 13 demonstrates how a newmodule is developed and integrated into NS2 through two following examples:Automatic Repeat reQuest (ARQ) and packet schedulers.

Chapter 14 summarizes the postsimulation process, which consists of three mainparts: debugging, variable and packet tracing, and result compilation.

Chapter 15 presents three helper modules: Timers, random number generators,and error models. It also discusses the concepts of two bit-wise operations – namely,bit masking and bit shifting, which are used throughout NS2.

Finally, Appendices A and B provide programming details which could be usefulfor the beginners. These details include an introduction to Tcl, OTcl, and AWKprogramming languages as well as a review of the polymorphism OOP concept.Last but not the least, Appendix C explains the BSD link list as well as bit levelfunctions used throughout this book.

x Preface

How to Read This Book

To Everyone

If you have not done so, we highly recommend you to visit the following onlinewebsites and learn what you can do with NS2.1

• Marc Greis’ Tutorial: http://www.isi.edu/nsnam/ns/tutorial• NS2 by Example: http://perform.wpi.edu/NS

To Beginners

Start simple. Learning how NS2 pass a packet from one end of a communicationlink to another is more challenging than what you might have imagined. In fact, ifthere is only one goal you should set, it is to understand this seemingly simple NS2mechanism. Once you grasp this concept, you can quickly and effortlessly learnother NS2 mechanism.

In particular, the following steps are suggested for beginners:

Step 1 (The Basic): Learn how NS2 pass packets from one object to anotherfrom within a SimpleLink. Visit Chap. 7 for SimpleLink implementation.You may need to visit Chaps. 4–5 for details of scheduler and Networkcomponent implementation.

Step 2 (CBR and UDP): These are two high-layer components which is easy tolearn. Look for the contents about UDP and CBR in Chaps. 9 and 11,respectively.

Step 3 (New Module): Next, visit Chap. 13 to learn how to build new modules intoNS2. There are two examples in this chapter. Note that you may need tolearn how to use make utility in Chap. 2.

To Instructors

This book contains 15 chapters. Different chapters may consume different amountof lecturing time. Generally, it requires more than 15 classes to cover the entirebook. We suggest instructors to emphasize/omit the contents of this book at theirdiscretion. In order to manage time efficiently, the instructors may follow thefollowing guidelines:

• Chapters 8, 14, and 10 can be skipped without greatly impairing the content ofthe course.

• The instructor may pack two chapters into one lecture: Chaps. 1–2 and 4–5.

1Some of these contents is available in Chap. 2.

Preface xi

We also provide exercises at the end of each chapter. The instructors mayuse these exercises to set up assignments, laboratory exercises, or examinationquestions.

What’s New in This Second Edition

In this Second edition of this book, we correct the grammatical and typologicalerrors. We add more materials on general computer network simulation into Chap. 1.We clean up the terminologies, include more examples, and rewrite Chaps. 6 and 15.At the end of each chapter, we provide exercises which can be used as assignments,laboratory exercises, and examination questions.

In Appendix A, we include most of the information that NS2 beginners need toknow about Tcl, OTcl, and AWK. During the NS2 learning process, readers mayencounter BSD-linked lists and bit level CCC functions. Readers may find theinformation about these two basic CCC components in Appendix C.

As of this writing, the latest NS2 version is 2.35. This version is not fullybackward-compatible with version 2.29 used as a reference in the first edition ofthis book. Therefore, we address the compatibility issues on the link error modulesin Chap. 15 and ARQ modules in Chap. 13.

We have received numerous requests to deal with wireless networking. In thisregard, we develop a new chapter, namely, Wireless Mobile Ad Hoc Networks(Chap. 12). In this chapter, we explain both packet forwarding over wireless linksand node mobility mechanism. The information about wireless trace formats isgiven in Chap. 14.

We have also developed companion online resources for this book. They containuseful NS2 information such as updates, discussion boards, detailed explanation onvarious topics, presentation slides, questions and answers, book corrections, and soon. The readers are highly encouraged to visit and join our online community at

• Website: http://ns2ultimate.com• Facebook Fan Page:

http://www.facebook.com/pages/Teerawat-Issariyakul/358240861417• Twitter feed: http://twitter.com/T Bear• Lecture notes: http://www.ece.ubc.ca/�teerawat/NS2.htm

TOT Public Company Limited Teerawat IssariyakulUniversity of Manitoba Ekram Hossain

Acknowledgment

In this second edition, we would like to express our sincere gratitude towardour colleagues at TOT Public Company Limited, and the graduate students ofthe “Wireless Communications, Networks, and Services Research Group” at theUniversity of Manitoba. We are deeply obliged to audience and followers at theNS2 website, the Facebook page, and the Twitter feed, as well as those who readthe previous edition of this book and took time contacting us. Your commentsand questions help us improve the content of the book in a big way. We areespecially thankful to Nestor Michael C. Tiglao who went so far to help us locatethe typographical errors.

We would like to thank Springer, the publisher of the book, for giving us anopportunity to share our knowledge and skill with our technical community. Specialthanks go to Brett Kurzman, Springer’s agent, who has keenly worked with us fromthe beginning to the end.

Last, but by no means the least, we would like to thank our families and friendsfor their understanding and continual moral support. We are forever indebted to allthe members of Issariyakul and Hossain families. Thank you for giving us love,support, encouragement, and most of all for never stopping to believe in us. Thankyou for not abandoning us and always being there for us, even if we have not givenyou time you deserved, and even have disappeared in a pile of NS2 codes.

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Contents

1 Simulation of Computer Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Computer Networks and the Layering Concept . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Layering Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.1.2 OSI and TCP/IP Reference Models . . . . . . . . . . . . . . . . . . . . . . 4

1.2 System Modeling .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.2.1 Analytical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.2.2 Simulation Approach.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3 Basics of Computer Network Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3.1 Simulation Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.3.2 Simulation Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.3.3 Confidence Interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.3.4 Choices for Network Simulation Tools . . . . . . . . . . . . . . . . . . 9

1.4 Time-Dependent Simulation .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.4.1 Time-Driven Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.4.2 Event-Driven Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.5 A Simulation Example: A Single-Channel Queuing System . . . . . . 141.5.1 Entities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.5.2 State Global Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151.5.3 Resource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151.5.4 Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151.5.5 Simulation Performance Measures

and Statistics Gatherers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161.5.6 Simulation Program .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.6 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191.7 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2 Introduction to Network Simulator 2 (NS2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.1 Introduction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.2 Basic Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

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2.3 Installation .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.3.1 Installing an All-In-One NS2 Suite

on Unix-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242.3.2 Installing an All-In-One NS2 Suite

on Windows-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242.4 Directories and Convention .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.4.1 Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.4.2 Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.5 Running NS2 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272.5.1 NS2 Program Invocation .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272.5.2 Main NS2 Simulation Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.6 A Simulation Example .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.7 Including C++ Modules into NS2 and the make Utility . . . . . . . . . . . 35

2.7.1 An Invocation of a make Utility . . . . . . . . . . . . . . . . . . . . . . . . . 352.7.2 A make Descriptor File. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352.7.3 NS2 Descriptor File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

2.8 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382.9 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3 Linkage Between OTcl and CCC in NS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413.1 The Two-Language Concept in NS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.1.1 The Natures of OTcl and CCCProgramming Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.1.2 CCC Programming Styles and Its Applicationin NS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

3.2 Class Binding .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.2.1 Class Binding Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.2.2 Defining Your Own Class Binding . . . . . . . . . . . . . . . . . . . . . . . 473.2.3 Naming Convention for Class TclClass . . . . . . . . . . . . . . 48

3.3 Variable Binding.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483.3.1 Variable Binding Methodology .. . . . . . . . . . . . . . . . . . . . . . . . . . 483.3.2 Setting the Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493.3.3 NS2 Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.3.4 Class Instvar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

3.4 Execution of CCC Statements from the OTcl Domain . . . . . . . . . . . . 533.4.1 OTcl Commands in a Nutshell. . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.4.2 The Internal Mechanism of OTcl Commands . . . . . . . . . . . 553.4.3 An Alternative for OTcl Command Invocation . . . . . . . . . . 593.4.4 Non-OOP Tcl Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593.4.5 Invoking a TclCommand.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

3.5 Shadow Object Construction Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623.5.1 A Handle of a TclObject . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623.5.2 TclObjects Construction Process . . . . . . . . . . . . . . . . . . . . . . . . . 633.5.3 TclObjects Destruction Process . . . . . . . . . . . . . . . . . . . . . . . . . . 67

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3.6 Access the OTcl Domain from the CCC Domain.. . . . . . . . . . . . . . . . . 673.6.1 Obtain a Reference to the Tcl Interpreter . . . . . . . . . . . . . . . . 683.6.2 Execution of Tcl Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683.6.3 Pass or Receive Results to/from the Interpreter .. . . . . . . . . 693.6.4 TclObject Reference Retrieval. . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

3.7 Translation of Tcl Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723.8 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733.9 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

4 Implementation of Discrete-Event Simulation in NS2 . . . . . . . . . . . . . . . . . . 774.1 NS2 Simulation Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774.2 Events and Handlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

4.2.1 An Overview of Events and Handlers . . . . . . . . . . . . . . . . . . . . 784.2.2 Class NsObject: A Child Class of Class

Handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794.2.3 Classes Packet and AtEvent: Child

Classes of Class Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804.3 The Scheduler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

4.3.1 Main Components of the Scheduler . . . . . . . . . . . . . . . . . . . . . . 824.3.2 Data Encapsulation and Polymorphism Concepts . . . . . . . 824.3.3 Main Functions of the Scheduler . . . . . . . . . . . . . . . . . . . . . . . . . 834.3.4 Two Auxiliary Functions.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854.3.5 Dynamics of the Unique ID of an Event . . . . . . . . . . . . . . . . . 864.3.6 Scheduling–Dispatching Mechanism . . . . . . . . . . . . . . . . . . . . 864.3.7 Null Event and Dummy Event Scheduling.. . . . . . . . . . . . . . 88

4.4 The Simulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894.4.1 Main Components of a Simulation . . . . . . . . . . . . . . . . . . . . . . . 894.4.2 Retrieving the Instance of the Simulator . . . . . . . . . . . . . . . . . 904.4.3 Simulator Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914.4.4 Running Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 924.4.5 Instprocs of OTcl Class Simulator. . . . . . . . . . . . . . . . . . . . . . . . 93

4.5 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934.6 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

5 Network Objects: Creation, Configuration,and Packet Forwarding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975.1 Overview of NS2 Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

5.1.1 Functionality-Based Classification of NS2 Modules . . . . 985.1.2 CCC Class Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

5.2 NsObjects: A Network Object Template . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.2.1 Class NsObject . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.2.2 Packet Forwarding Mechanism of NsObjects. . . . . . . . . . . . 101

5.3 Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1015.3.1 Class Declaration .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1025.3.2 OTcl Configuration Commands . . . . . . . . . . . . . . . . . . . . . . . . . . 1035.3.3 Packet Forwarding Mechanism of Connectors . . . . . . . . . . 106

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5.4 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1085.5 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

6 Nodes as Routers or Computer Hosts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1116.1 An Overview of Nodes in NS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

6.1.1 Routing Concept and Terminology .. . . . . . . . . . . . . . . . . . . . . . 1116.1.2 Architecture of a Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1126.1.3 Default Nodes and Node Configuration Interface . . . . . . . 113

6.2 Classifiers: Multi-Target Packet Forwarders . . . . . . . . . . . . . . . . . . . . . . . . 1146.2.1 Class Classifier and Its Main Components. . . . . . . . . 1146.2.2 Port Classifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186.2.3 Hash Classifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1196.2.4 Creating Your Own Classifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

6.3 Routing Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1256.3.1 An Overview of Routing Modules . . . . . . . . . . . . . . . . . . . . . . . 1256.3.2 CCC Class RoutingModule . . . . . . . . . . . . . . . . . . . . . . . . . . 1266.3.3 OTcl Class RtModule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1296.3.4 Built-in Routing Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

6.4 Route Logic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326.4.1 CCC Implementation.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326.4.2 OTcl Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

6.5 Node Construction and Configuration.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346.5.1 Key Variables of the OTcl Class Node

and Their Relationship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1356.5.2 Installing Classifiers in a Node . . . . . . . . . . . . . . . . . . . . . . . . . . . 1376.5.3 Bridging a Node to a Transport Layer Protocol . . . . . . . . . 1386.5.4 Adding/Deleting a Routing Rule . . . . . . . . . . . . . . . . . . . . . . . . . 1406.5.5 Node Construction and Configuration.. . . . . . . . . . . . . . . . . . . 140

6.6 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1476.7 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

7 Link and Buffer Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1517.1 Introduction to SimpleLink Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

7.1.1 Main Components of a SimpleLink . . . . . . . . . . . . . . . . . . . . . . 1517.1.2 Instprocs for Configuring a SimpleLink Object . . . . . . 1537.1.3 The Constructor of Class SimpleLink . . . . . . . . . . . . . . . . 154

7.2 Modeling Packet Departure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1557.2.1 Packet Departure Mechanism.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1557.2.2 CCC Class LinkDelay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

7.3 Buffer Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1587.3.1 Class PacketQueue: A Model for Packet Buffering.. 1597.3.2 Queue Handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1607.3.3 Queue Blocking and Callback Mechanism . . . . . . . . . . . . . . 1617.3.4 Class DropTail: A Child Class of Class Queue . . . . . . 163

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7.4 A Sample Two-Node Network.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1657.4.1 Network Construction.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1657.4.2 Packet Flow Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

7.5 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1667.6 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

8 Packets, Packet Headers, and Header Format . . . . . . . . . . . . . . . . . . . . . . . . . . 1698.1 An Overview of Packet Modeling Principle . . . . . . . . . . . . . . . . . . . . . . . . 169

8.1.1 Packet Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1698.1.2 A Packet as an Event: A Delayed Packet

Reception Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1728.1.3 A Link List of Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1738.1.4 Free Packet List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

8.2 Packet Allocation and Deallocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1758.2.1 Packet Allocation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1758.2.2 Packet Deallocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

8.3 Packet Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1808.3.1 An Overview of First Level Packet

Composition: Offseting Protocol-SpecificHeader on the Packet Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181

8.3.2 Common Packet Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1828.3.3 IP Packet Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1838.3.4 Payload Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1848.3.5 Protocol-Specific Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1868.3.6 Packet Header Access Mechanism . . . . . . . . . . . . . . . . . . . . . . . 1908.3.7 Packet Header Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1938.3.8 Protocol-Specific Header Composition

and Packet Header Construction. . . . . . . . . . . . . . . . . . . . . . . . . . 1948.4 Data Payload.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2008.5 Customizing Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

8.5.1 Creating Your Own Packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2028.5.2 Activate/Deactivate a Protocol-Specific Header . . . . . . . . . 205

8.6 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2068.7 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

9 Transport Control Protocols Part 1:An Overview and User Datagram Protocol Implementation . . . . . . . . . . 2099.1 UDP and TCP Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

9.1.1 UDP Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2099.1.2 TCP Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

9.2 Basic Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2149.2.1 Applications, Agents, and a Low-Level Network . . . . . . . 2159.2.2 Agent Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2179.2.3 Internal Mechanism for Agents. . . . . . . . . . . . . . . . . . . . . . . . . . . 2189.2.4 Guidelines to Define a New Transport Layer Agent . . . . . 222

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9.3 UDP and Null Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2229.3.1 Null (Receiving) Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2229.3.2 UDP (Sending) Agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2239.3.3 Setting Up a UDP Connection .. . . . . . . . . . . . . . . . . . . . . . . . . . . 227

9.4 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2279.5 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

10 Transport Control Protocols Part 2:Transmission Control Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22910.1 An Overview of TCP Agents in NS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

10.1.1 Setting Up a TCP Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22910.1.2 Packet Transmission and Acknowledgment

Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23010.1.3 TCP Header. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23110.1.4 Defining TCP Sender and Receiver . . . . . . . . . . . . . . . . . . . . . . 231

10.2 TCP Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23510.2.1 Class Acker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23710.2.2 Class TcpSink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240

10.3 TCP Sender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24210.4 TCP Packet Transmission Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

10.4.1 Function sendmsg(nbytes) . . . . . . . . . . . . . . . . . . . . . . . . . . 24310.4.2 Function send much(force,reason,

maxburst) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24410.4.3 Function output(seqno,reason) . . . . . . . . . . . . . . . . . 24610.4.4 Function send one() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248

10.5 ACK Processing Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24910.5.1 Function recv(p,h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25010.5.2 Function recv newack helper(pkt) . . . . . . . . . . . . . . 25110.5.3 Function newack(pkt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25310.5.4 Function dupack action() . . . . . . . . . . . . . . . . . . . . . . . . . . 253

10.6 Timer-Related Functions .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25410.6.1 RTT Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25410.6.2 RTT Estimation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25610.6.3 Overview of State Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25710.6.4 Retransmission Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25810.6.5 Function Overview .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25910.6.6 Function rtt update(tao) . . . . . . . . . . . . . . . . . . . . . . . . . . 26010.6.7 Function rtt timeout() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26210.6.8 Function rtt backoff() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26310.6.9 Function set rtx timer()and Function

reset rtx timer(mild,backoff) . . . . . . . . . . . . . . 26410.6.10 Function newtimer(pkt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26410.6.11 Function timeout(tno) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265

10.7 Window Adjustment Functions .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26710.7.1 Function opencwnd() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26810.7.2 Function slowdown(how) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

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10.8 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27110.9 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

11 Application: User Demand Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27311.1 Relationship Between an Application and a Transport

Layer Agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27311.2 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276

11.2.1 Functions of Classes Application and Agent . . . . . . 27711.2.2 Public Functions of Class Application . . . . . . . . . . . . . . 27811.2.3 Related Public Functions of Class Agent . . . . . . . . . . . . . . . 28011.2.4 OTcl Commands of Class Application . . . . . . . . . . . . . . 280

11.3 Traffic Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28011.3.1 An Overview of Class TrafficGenerator . . . . . . . . . 28111.3.2 Main Mechanism of a Traffic Generator . . . . . . . . . . . . . . . . . 28311.3.3 Built-in Traffic Generators in NS2 . . . . . . . . . . . . . . . . . . . . . . . 28411.3.4 Class CBR Traffic: An Example Traffic

Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28711.4 Simulated Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

11.4.1 File Transfer Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29011.4.2 Telnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290

11.5 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29111.6 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292

12 Wireless Mobile Ad Hoc Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29312.1 An Overview of Wireless Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

12.1.1 Mobile Node. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29412.1.2 Architecture of Mobile Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29412.1.3 General Packet Flow in a Wireless Network

Implementation .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29712.1.4 Mobile Node Configuration Process . . . . . . . . . . . . . . . . . . . . . 298

12.2 Network Layer: Routing Agents and Routing Protocols . . . . . . . . . . . 30512.2.1 Preliminaries for the AODV Routing Protocol . . . . . . . . . . 30512.2.2 The Principles of AODV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30612.2.3 An Overview of AODV Implementation in NS2 . . . . . . . . 30812.2.4 AODV Routing Agent Construction Process . . . . . . . . . . . . 31112.2.5 General Packet Flow Mechanism

in a Wireless Network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31212.2.6 Packet Reception and Processing Function of AODV .. . 31212.2.7 AODV Time-Driven Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

12.3 Data Link Layer: Link Layer Models, AddressResolution Protocols, and Interface Queues . . . . . . . . . . . . . . . . . . . . . . . . 31512.3.1 Link Layer Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31512.3.2 Address Resolution Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31512.3.3 Interface Queues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

12.4 Medium Access Control Layer: IEEE 802.11 . . . . . . . . . . . . . . . . . . . . . . 31712.4.1 Description of IEEE 802.11 MAC Protocol . . . . . . . . . . . . . 31812.4.2 NS2 Classes Mac and Mac802 11 . . . . . . . . . . . . . . . . . . . . . . 319

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12.4.3 Basic Functions of NS2 Classes Macand Mac802 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

12.4.4 Timer Concepts for Implementation of IEEE 802.11 . . . 32312.4.5 Packet Reception Mechanism of IEEE 802.11 . . . . . . . . . . 32312.4.6 Implementation of Packet Retransmission in NS2 . . . . . . 32612.4.7 Implementation of Carrier-Sensing, Backoff,

and NAV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32912.5 Physical Layer: Physical Network Interfaces and Channel . . . . . . . . 331

12.5.1 Physical Network Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33112.5.2 Wireless Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33312.5.3 Sender Operations at the Physical Layer . . . . . . . . . . . . . . . . . 33312.5.4 Receiver Operations at the Physical Layer . . . . . . . . . . . . . . . 334

12.6 An Introduction to Node Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33712.6.1 Basic Mobility Configuration .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 33712.6.2 General Operation Director . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33812.6.3 Random Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33912.6.4 Mobility and Traffic Generators: Standalone

Helper Utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34012.7 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34312.8 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

13 Developing New Modules for NS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34513.1 Automatic Repeat reQuest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

13.1.1 The Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34613.1.2 CCC Implementation.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34813.1.3 OTcl Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35413.1.4 ARQ Under a Delayed (Error-Free)

Feedback Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35713.2 Packet Scheduling for Multi-Flow Data Transmission . . . . . . . . . . . . . 359

13.2.1 The Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35913.2.2 CCC Implementation.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36013.2.3 OTcl Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

13.3 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36713.4 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368

14 Postsimulation Processing: Debugging, Tracing,and Result Compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36914.1 Debugging: A Process to Remove Programming Errors . . . . . . . . . . . 369

14.1.1 Types of Programming Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36914.1.2 Debugging Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371

14.2 Variable Tracing .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37414.2.1 Activation Process for Variable Tracing.. . . . . . . . . . . . . . . . . 37414.2.2 Traceable Variable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37514.2.3 Components and Architecture for Variable Tracing . . . . . 37614.2.4 Tracing in Action: An Example of Class TcpAgent . . . 38114.2.5 Setting Up Variable Tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381

Contents xxiii

14.3 Packet Tracing .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38414.3.1 OTcl Configuration Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38514.3.2 CCC Main Packet Tracing Class Trace . . . . . . . . . . . . . . . 38914.3.3 CCC Helper Class BaseTrace . . . . . . . . . . . . . . . . . . . . . 39214.3.4 Various Types of Packet Tracing Objects . . . . . . . . . . . . . . . . 39414.3.5 Format of Trace Strings for Packet Tracing .. . . . . . . . . . . . . 397

14.4 Compilation of Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40214.5 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40614.6 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

15 Related Helper Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40915.1 Timers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

15.1.1 Implementation Concept of Timer in NS2 . . . . . . . . . . . . . . . 40915.1.2 OTcl Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41115.1.3 CCC Class Implementation .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41315.1.4 Guidelines for Implementing Timers in NS2 . . . . . . . . . . . . 423

15.2 Implementation of Random Numbers in NS2 . . . . . . . . . . . . . . . . . . . . . . 42415.2.1 Random Number Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42415.2.2 Seeding a Random Number Generator . . . . . . . . . . . . . . . . . . . 42515.2.3 OTcl and CCC Implementation.. . . . . . . . . . . . . . . . . . . . . . . . . 42715.2.4 Randomness in Simulation Scenarios . . . . . . . . . . . . . . . . . . . . 42915.2.5 Random Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43115.2.6 Guidelines for Random Number Generation

in NS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43415.3 Built-in Error Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435

15.3.1 OTcl Implementation: Error Model Configuration . . . . . . 43615.3.2 CCC Implementation: Error Model Simulation . . . . . . . . 44015.3.3 Guidelines for Implementing a New Error

Model in NS2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44815.4 Bit Operations in NS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449

15.4.1 Bit Masking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44915.4.2 Bit Shifting and Decimal Multiplication .. . . . . . . . . . . . . . . . 451

15.5 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45215.6 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452

A Programming Essentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455A.1 Tcl Programming .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455

A.1.1 Program Invocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455A.1.2 Syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456A.1.3 Variables and Basic Operations.. . . . . . . . . . . . . . . . . . . . . . . . . . 457A.1.4 Logical and Mathematical Operations . . . . . . . . . . . . . . . . . . . 460A.1.5 Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461A.1.6 Modularization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463A.1.7 Advanced Input/Output: Files and Channels. . . . . . . . . . . . . 465A.1.8 Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467

xxiv Contents

A.2 Objected-Oriented Tcl Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469A.2.1 OTcl Language Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470A.2.2 Classes and Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470A.2.3 Objects and Object Construction Process . . . . . . . . . . . . . . . . 471A.2.4 Member Variables and Functions. . . . . . . . . . . . . . . . . . . . . . . . . 472A.2.5 A List of Useful Instance Procedures . . . . . . . . . . . . . . . . . . . . 474

A.3 AWK Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476A.3.1 Program Invocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477A.3.2 An AWK Script. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478A.3.3 AWK Programming Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478A.3.4 Pattern Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479A.3.5 Basic Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479A.3.6 Redirection and Output to Files . . . . . . . . . . . . . . . . . . . . . . . . . . 481A.3.7 Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

A.4 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

B A Review of the Polymorphism Concept in OOP . . . . . . . . . . . . . . . . . . . . . . . 485B.1 Fundamentals of Polymorphism .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485B.2 Type Casting and Function Ambiguity .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488B.3 Virtual Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489B.4 Abstract Classes and Pure Virtual Functions. . . . . . . . . . . . . . . . . . . . . . . . 490B.5 Class Composition: An Application of Type Casting

Polymorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491B.6 Programming Polymorphism with No Type Casting:

An Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492B.7 A Scalability Problem Caused by Non-Type Casting

Polymorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493B.8 The Class Composition Programming Concept . . . . . . . . . . . . . . . . . . . . 494

C BSD Link List and Bit Level Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499C.1 BSD Link List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499C.2 Bit Level Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501

General Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503

Code Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507