Computer Networks ASystem Approach 4thed

EDITION
4
COMPUTER
NETWORKS
A SYSTEMS APPROACH
The Morgan Kaufmann Series in Networking
Series Editor, David Clark, M.I.T.
Computer Networks: A Systems Approach, 4e
Larry L. Peterson and Bruce S. Davie
Network Routing: Algorithms, Protocols, and
Architectures
Deepankar Medhi and Karthikeyan Ramaswami
Deploying IP and MPLS QoS for Multiservice Networks:
Theory and Practice
John Evans and Clarence Filsfils
Traffic Engineering and QoS Optimization of Integrated
Voice & Data Networks
Gerald R. Ash
IPv6 Core Protocols Implementation
Qing Li, Tatuya Jinmei, and Keiichi Shima
Smart Phone and Next-Generation Mobile Computing
Pei Zheng and Lionel Ni
GMPLS: Architecture and Applications
Adrian Farrel and Igor Bryskin
Network Security: A Practical Approach
Jan L. Harrington
Content Networking: Architecture, Protocols, and Practice
Markus Hofmann and Leland R. Beaumont
Network Algorithmics: An Interdisciplinary Approach to
Designing Fast Networked Devices

George Varghese
Network Recovery: Protection and Restoration of Optical,
SONET-SDH, IP, and MPLS
Jean Philippe Vasseur, Mario Pickavet, and Piet
Demeester
Routing, Flow, and Capacity Design in Communication
and Computer Networks
Michał Pióro and Deepankar Medhi
Wireless Sensor Networks: An Information Processing
Approach
Feng Zhao and Leonidas Guibas
Communication Networking: An Analytical Approach
Anurag Kumar, D. Manjunath, and Joy Kuri
The Internet and Its Protocols: A Comparative Approach
Adrian Farrel
Modern Cable Television Technology: Video, Voice, and
Data Communications, 2e
Walter Ciciora, James Farmer, David Large, and
Michael Adams
Bluetooth Application Programming with the Java APIs
C Bala Kumar, Paul J. Kline, and Timothy J.
Thompson
Policy-Based Network Management: Solutions for the
Next Generation
John Strassner
Network Architecture, Analysis, and Design, 2e
James D. McCabe
MPLS Network Management: MIBs, Tools, and
Te c h n i q u e s
Thomas D. Nadeau

Developing IP-Based Services: Solutions for Service
Providers and Vendors
Monique Morrow and Kateel Vijayananda
Telecommunications Law in the Internet Age
Sharon K. Black
Optical Networks: A Practical Perspective, 2e
Rajiv Ramaswami and Kumar N. Sivarajan
Internet QoS: Architectures and Mechanisms
Zheng Wang
TCP/IP Sockets in Java: Practical Guide for Programmers
Michael J. Donahoo and Kenneth L. Calvert
TCP/IP Sockets in C: Practical Guide for Programmers
Kenneth L. Calvert and Michael J. Donahoo
Multicast Communication: Protocols, Programming, and
Applications
Ralph Wittmann and Martina Zitterbart
MPLS: Technology and Applications
Bruce Davie and Yakov Rekhter
High-Performance Communication Networks, 2e
Jean Walrand and Pravin Varaiya
Internetworking Multimedia
Jon Crowcroft, Mark Handley, and Ian Wakeman
Understanding Networked Applications: A First Course
David G. Messerschmitt
Integrated Management of Networked Systems: Concepts,
Architectures, and Their Operational
Application
Heinz-Gerd Hegering, Sebastian Abeck, and
Bernhard Neumair
Virtual Private Networks: Making the Right Connection

Dennis Fowler
Networked Applications: A Guide to the New Computing
Infrastructure
David G. Messerschmitt
Wide Area Network Design: Concepts and Tools for
Optimization
Robert S. Cahn
For further information on these books and for a list of forthcoming titles, please visit our Web site at
.
EDITION
4
COMPUTER
NETWORKS
A SYSTEMS APPROACH
Larry L. Peterson & Bruce S. Davie
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ISBN 13: 978-0-12-370548-8 (Case bound)
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Peterson, Larry L.
Computer networks : a systems approach / Larry L. Peterson & Bruce S.
Davi – 4th ed.
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Includes bibliographical references and index.
ISBN-13: 978-0-12-370548-8 (hardcover : alk. paper)
ISBN-10: 0-12-370548-7 (hardcover : alk. paper)
ISBN-13: 978-0-12-374013-7 (pbk. : alk. paper)
ISBN-10: 0-12-374013-4 (pbk. : alk. paper) 1. Computer networks. I.

Davie, Bruce S. II. Title.
TK5105.5.P479 2007
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2006102454
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Printed in the United States of America.
06 07 08 09 10 5 4 3 2 1
To Lee Peterson and Robert Davie

FOREWORD
David D. Clark
Massachusetts Institute of Technology
t is now ten years since this classic book first appeared. Looking back, it is amazing
I
what has happened in that time. We have seen the transformation of the Web from
a small experiment to a World Wide phenomenon. We have seen the emergence
of voice over IP and peer-to-peer content sharing. We have seen technology speed up
a hundred-fold, the emergence of broadband to the home, and the rise of botnets and
other horrid security problems. Many things have changed, technology has come and
gone, and (perhaps equally amazing) much of the basics of the Internet are still there.
This book, too, has changed much in ten years, with four editions to keep up. But
the basic value of the book remains the same as the first edition. This book gives you the
facts you need, and puts those facts into the larger context so that the knowledge you
gain will be of value even as the details change. Reading this book informs you about
today and prepares you for tomorrow. One new feature is a set of sidebars that illustrate
the context of ideas being presented in the text—the why of the ideas. Why did an idea
fail? Why did it succeed?
What has changed in the book? Some technologies have faded from sight, and get
less attention in this edition. We bid a fond farewell to FDDI and ATM LANs. Some

technologies have mutated and emerged in new forms. Remote Procedure Call is no
longer a LAN-based low-level invocation mechanism, but the foundation of Internet-
wide Web Services. We welcome gigabit Ethernet, an updated and expanded section on
wireless, and more on router implementation. The material on TCP is up to date, with
discussion of new acknowledgment schemes and extensions for high speed.
With the increasing concern with security, there is a completely revised chapter
with a new emphasis on a systems approach to security, and a discussion of threats and
how to counter them. And at the end, there is a chapter that helps you “put it all to-
gether,” using case studies at the application layer (VOIP, multimedia, and peer to peer)
to show how all the concepts from the previous chapters combine to provide the system
that supports these applications.
viii Foreword
The evolution of networks is not going to slow down. Soon we will be talking
about the impact of television over IP, the collision of the Internet and sensor networks,
and lots of other very new and exciting ideas. But relax—if you read this book today you
will have the insights you need for tomorrow.
FOREWORD TO THE FIRST EDITION
David Clark
Massachusetts Institute of Technology
he term spaghetti code is universally understood as an insult. All good computer
T
scientists worship the god of modularity, since modularity brings many benefits,
including the all-powerful benefit of not having to understand all parts of a
problem at the same time in order to solve it. Modularity thus plays a role in presenting
ideas in a book, as well as in writing code. If a book’s material is organized effectively—
modularly—the reader can start at the beginning and actually make it to the end.
The field of network protocols is perhaps unique in that the “proper” modularity
has been handed down to us in the form of an international standard: the seven-layer
reference model of network protocols from the ISO. This model, which reflects a layered
approach to modularity, is almost universally used as a starting point for discussions of

protocol organization, whether the design in question conforms to the model or deviates
from it.
It seems obvious to organize a networking book around this layered model. How-
ever, there is a peril to doing so, because the OSI model is not really successful at organiz-
ing the core concepts of networking. Such basic requirements as reliability, flow control,
or security can be addressed at most, if not all, of the OSI layers. This fact has led to
great confusion in trying to understand the reference model. At times it even requires a
suspension of disbelief. Indeed, a book organized strictly according to a layered model
has some of the attributes of spaghetti code.
Which brings us to this book. Peterson and Davie follow the traditional layered
model, but they do not pretend that this model actually helps in the understanding
of the big issues in networking. Instead, the authors organize discussion of fundamen-
tal concepts in a way that is independent of layering. Thus, after reading the book,
readers will understand flow control, congestion control, reliability enhancement, data
representation, and synchronization, and will separately understand the implications of
addressing these issues in one or another of the traditional layers.
This is a timely book. It looks at the important protocols in use today—especially
the Internet protocols. Peterson and Davie have a long involvement in and much ex-
x Foreword to the First Edition
perience with the Internet. Thus their book reflects not just the theoretical issues in
protocol design, but the real factors that matter in practice. The book looks at some of
the protocols that are just emerging now, so the reader can be assured of an up-to-date
perspective. But most importantly, the discussion of basic issues is presented in a way
that derives from the fundamental nature of the problem, not the constraints of the lay-
ered reference model or the details of today’s protocols. In this regard, what this book
presents is both timely and timeless. The combination of real-world relevance, current
examples, and careful explanation of fundamentals makes this book unique.
PREFACE
hen the first edition of this book was published in 1996, it was a novelty to
W

be able to order merchandise on the Internet, and a company that advertised
its domain name was considered cutting edge. Today, Internet commerce
is a fact of life, and “.com” stocks have gone through an entire boom and bust cycle.
A host of new technologies ranging from optical switches to wireless networks are now
becoming mainstream. It seems the only predictable thing about the Internet is constant
change.
Despite these changes the question we asked in the first edition is just as valid
today: What are the underlying concepts and technologies that make the Internet work?
The answer is that much of the TCP/IP architecture continues to function just as was
envisioned by its creators more than 30 years ago. This isn’t to say that the Internet
architecture is uninteresting; quite the contrary. Understanding the design principles that
underly an architecture that has not only survived but fostered the kind of growth and
change that the Internet has seen over the past three decades is precisely the right place
to start. Like the previous editions, the third edition makes the “why” of the Internet
architecture its cornerstone.
Audience
Our intent is that the book should serve as the text for a comprehensive networking
class, at either the graduate or upper-division undergraduate level. We also believe that
the book’s focus on core concepts should be appealing to industry professionals who are
retraining for network-related assignments, as well as current network practitioners who
want to understand the “whys” behind the protocols they work with every day and to see
the big picture of networking.
It is our experience that both students and professionals learning about networks
for the first time often have the impression that network protocols are some sort of edict
handed down from on high, and that their job is to learn as many TLAs (three-letter
acronyms) as possible. In fact, protocols are the building blocks of a complex system
developed through the application of engineering design principles. Moreover, they are
constantly being refined, extended, and replaced based on real-world experience. With
xii Preface
this in mind, our goal with this book is to do more than survey the protocols in use

today. Instead, we explain the underlying principles of sound network design. We feel
that this grasp of underlying principles is the best tool for handling the rate of change in
the networking field.
Changes in the Fourth Edition
Even though our focus is on the underlying principles of networking, we illustrate these
principles using examples from today’s working Internet. Therefore, we added a signifi-
cant amount of new material to track many of the important recent advances in network-
ing. We also deleted, reorganized, and changed the focus of existing material to reflect
changes that have taken place over the past decade.
Perhaps the most significant change we have noticed since writing the first edition
is that almost every reader now has some familiarity with networked applications such as
the World Wide Web and email. For this reason, we have increased the focus on applica-
tions, starting in the first chapter. We use applications as the motivation for the study of
networking, and to derive a set of requirements that a useful network must meet if it is
to support both current and future applications on a global scale. However, we retain the
problem-solving approach of previous editions that starts with the problem of intercon-
necting hosts and works its way up the layers to conclude with a detailed examination
of application layer issues. We believe it is important to make the topics covered in the
book relevant by starting with applications and their needs. At the same time, we feel
that higher-layer issues, such as application layer and transport layer protocols, are best
understood after the basic problems of connecting hosts and switching packets have been
explained.
As we did in the second and third editions, we have added or increased coverage of
important new topics, and brought other topics up to date. Major new or substantially
updated topics in this edition are:
■ Comprehensively revised and updated coverage of security, with a focus on
building secure systems, not just on cryptographic algorithms;
■ Expanded and updated coverage of XML (extensible markup language);
■ An updated section on overlay networks, including “peer-to-peer” networking
and “content distribution networks”;

■ A new section on web services, including the SOAP and REST (Representa-
tional State Transfer) architectures;
Preface xiii
■ Updated material on wireless technology, including the 802.11 (WiFi) and
802.16 (WiMAX) standards as well as cellular wireless technologies including
the 3G (third generation) standards;
■ Expanded coverage of interdomain routing;
■ Expanded coverage on protocols and quality of service for multimedia applica-
tions such as voiceover IP (VOIP) and video streaming;
■ Updated coverage of congestion control mechanisms, particularly for high
bandwidth-delay product networks.
In addition, we have added a new feature to this edition: “Where are they now?”
sidebars. These short discussions focus on the success and failure of protocols in the real
world. Sometimes they describe a protocol that most people have written off but which
is actually enjoying unheralded success; other times they trace the fate of a protocol
that failed to thrive over the long run. The goal of these sidebars is to make the material
relevant by showing how technologies have fared in the competitive world of networking.
Approach
For an area that’s as dynamic and changing as computer networks, the most important
thing a textbook can offer is perspective—to distinguish between what’s important and
what’s not, and between what’s lasting and what’s superficial. Based on our experience
over the past 20-plus years doing research that has led to new networking technology,
teaching undergraduate and graduate students about the latest trends in networking, and
delivering advanced networking products to market, we have developed a perspective—
which we call the systems approach—that forms the soul of this book. The systems ap-
proach has several implications:
■ Rather than accept existing artifacts as gospel, we start first with principles and
walk you through the thought process that led to today’s networks. This allows
us to explain why networks look like they do. It is our experience that once you
understand the underlying concepts, any new protocol that you are confronted

with will be relatively easy to digest.
■ Although the material is loosely organized around the traditional network lay-
ers, starting at the bottom and moving up the protocol stack, we do not adopt
a rigidly layerist approach. Many topics—congestion control and security are
good examples—have implications up and down the hierarchy, and so we dis-
cuss them outside the traditional layered model. In short, we believe layering
makes a good servant but a poor master; it’s more often useful to take an end-
to-end perspective.
xiv Preface
■ Rather than explain how protocols work in the abstract, we use the most im-
portant protocols in use today—many of them from the TCP/IP Internet—to
illustrate how networks work in practice. This allows us to include real-world
experiences in the discussion.
■ Although at the lowest levels networks are constructed from commodity hard-
ware that can be bought from computer vendors and communication services
that can be leased from the phone company, it is the software that allows net-
works to provide new services and adapt quickly to changing circumstances. It is
for this reason that we emphasize how network software is implemented, rather
than stopping with a description of the abstract algorithms involved. We also
include code segments taken from a working protocol stack to illustrate how
you might implement certain protocols and algorithms.
■ Networks are constructed from many building-block pieces, and while it is nec-
essary to be able to abstract away uninteresting elements when solving a particu-
lar problem, it is essential to understand how all the pieces fit together to form a
functioning network. We therefore spend considerable time explaining the over-
all end-to-end behavior of networks, not just the individual components, so that
it is possible to understand how a complete network operates, all the way from
the application to the hardware.
■ The systems approach implies doing experimental performance studies, and
then using the data you gather both to quantitatively analyze various design

options and to guide you in optimizing the implementation. This emphasis on
empirical analysis pervades the book.
■ Networks are like other computer systems—for example, operating systems,
processor architectures, distributed and parallel systems, and so on. They are all
large and complex. To help manage this complexity, system builders often draw
on a collection of design principles. We highlight these design principles as they
are introduced throughout the book, illustrated, of course, with examples from
computer networks.
Pedagogy and Features
The fourth edition retains several features from prior editions, and adds one more, that
we encourage you to take advantage of:
■ Problem statements. At the start of each chapter, we describe a problem that
identifies the next set of issues that must be addressed in the design of a network.
This statement introduces and motivates the issues to be explored in the chapter.
Preface xv
■ Shaded sidebars. Throughout the text, shaded sidebars elaborate on the topic be-
ing discussed or introduce a related advanced topic. In many cases, these sidebars
relate real-world anecdotes about networking.
■ “Where are they now?” sidebars. These new elements trace the success and failure
of protocols in real-world deployment.
■ Highlighted paragraphs. These paragraphs summarize an important nugget of
information that we want you to take away from the discussion, such as a widely
applicable system design principle.
■ Real protocols. Even though the book’s focus is on core concepts rather than ex-
isting protocol specifications, real protocols are used to illustrate most of the
important ideas. As a result, the book can be used as a source of reference for
many protocols. To help you find the descriptions of the protocols, each ap-
plicable section heading parenthetically identifies the protocols described in that
section. For example, Section 5.2, which describes the principles of reliable end-
to-end protocols, provides a detailed description of TCP, the canonical example

of such a protocol.
■ Open issues. We conclude the main body of each chapter with an important
issue that is currently being debated in the research community, the commercial
world, or society as a whole. We have found that discussing these issues helps to
make the subject of networking more relevant and exciting.
■ Recommended reading. These highly selective lists appear at the end of each chap-
ter. Each list generally contains the seminal papers on the topics just discussed.
We strongly recommend that advanced readers (e.g., graduate students) study
the papers in this reading list to supplement the material covered in the chapter.
Road Map and Course Use
The book is organized as follows:
■ Chapter 1 introduces the set of core ideas that are used throughout the rest of the
text. Motivated by widespread applications, it discusses what goes into a network
architecture, provides an introduction to protocol implementation issues, and
defines the quantitative performance metrics that often drive network design.
■ Chapter 2 surveys a wide range of low-level network technologies, ranging from
Ethernet to token ring to wireless. It also describes many of the issues that
all data link protocols must address, including encoding, framing, and error
detection.
xvi Preface
■ Chapter 3 introduces the basic models of switched networks (datagrams versus
virtual circuits) and describes two prevalent switching technologies—switched
Ethernet and ATM—in some detail. It also discusses the design of hardware-
based switches.
■ Chapter 4 introduces internetworking and describes the key elements of the
Internet Protocol (IP). A central question addressed in this chapter is how net-
works that scale to the size of the Internet are able to route packets. Unicast,
multicast, and interdomain routing are covered.
■ Chapter 5 moves up to the transport level, describing both the Internet’s Trans-
mission Control Protocol (TCP) and Remote Procedure Call (RPC) used to

build client-server applications in detail. The Real-time Transport Protocol
(RTP), which supports multimedia applications, is also described.
■ Chapter 6 discusses congestion control and resource allocation. The issues in
this chapter cut across both the network level (Chapters 3 and 4) and the trans-
port level (Chapter 5). Of particular note, this chapter describes how congestion
control works in TCP, and it introduces the mechanisms used to provide quality
of service in IP.
■ Chapter 7 considers the data sent through a network. This includes both the
problems of presentation formatting and data compression. XML is covered
here, and the compression section includes explanations of how MPEG video
compression and MP3 audio compression work.
■ Chapter 8 discusses network security, beginning with an overview of crypto-
graphic tools, the problems of key distribution, and a discussion of several
authentication techniques using both public and private keys. The main fo-
cus of this chapter is the building of secure systems, using examples including
Pretty Good Privacy (PGP), Secure Shell (SSH), and the IP Security architecture
(IPSEC). Firewalls are also covered here.
■ Chapter 9 describes a representative sample of network applications and the
protocols they use, including traditional applications like email and the Web,
multimedia applications such as IP telephony and video streaming, and overlay
networks like peer-to-peer file sharing and content distribution networks. The
Web Services architectures for developing new application protocols are also
presented here.
For an undergraduate course, extra class time will most likely be needed to help
students digest the introductory material in the first chapter, probably at the expense
Preface xvii
of the more advanced topics covered in Chapters 6 through 8. Chapter 9 then returns
to the popular topic of network applications. In contrast, the instructor for a graduate
course should be able to cover the first chapter in only a lecture or two—with students
studying the material more carefully on their own—thereby freeing up additional class

time to cover the last four chapters in depth. Both graduate and undergraduate classes
will want to cover the core material contained in the middle four chapters (Chapters
2–5), although an undergraduate class might choose to skim the more advanced sections
(e.g., Sections 2.2, 4.4, and 4.5).
For those of you using the book in self-study, we believe that the topics we have
selected cover the core of computer networking, and so we recommend that the book
be read sequentially, from front to back. In addition, we have included a liberal supply
of references to help you locate supplementary material that is relevant to your specific
areas of interest, and we have included solutions to select exercises.
The book takes a unique approach to the topic of congestion control by pulling all
topics related to congestion control and resource allocation together in a single place—
Chapter 6. We do this because the problem of congestion control cannot be solved at
any one level, and we want you to consider the various design options at the same time.
(This is consistent with our view that strict layering often obscures important design
trade-offs.) A more traditional treatment of congestion control is possible, however, by
studying Section 6.2 in the context of Chapter 3 and Section 6.4 in the context of
Chapter 5.
Exercises
Significant effort has gone into improving the exercises with each new edition. In the
second edition we greatly increased the number of problems and, based on class testing,
dramatically improved their quality. In the third edition we made two other important
changes, which we retained here:
■ For those exercises that we felt are particularly challenging or require special
knowledge not provided in the book (e.g., probability expertise), we have added
an icon
★ to indicate the extra level of difficulty.
■ In each chapter we added some extra representative exercises for which worked
solutions are provided at the back of the book. These exercises, marked
✓,are
intended to provide some help in tackling the other exercises in the book.

In this edition we have added new exercises to reflect the updated content. The
current set of exercises are of several different styles:
xviii Preface
■ Analytical exercises that ask the student to do simple algebraic calculations that
demonstrate their understanding of fundamental relationships.
■ Design questions that ask the student to propose and evaluate protocols for
various circumstances.
■ Hands-on questions that ask the student to write a few lines of code to test an
idea or to experiment with an existing network utility.
■ Library research questions that ask the student to learn more about a particular
topic.
Also, as described in more detail below, socket-based programming assignments, as
well as simulation labs, are available online.
Supplemental Materials and Online Resources
To assist instructors, we have prepared an instructor’s manual that contains solutions to
selected exercises. The manual is available from the publisher.
Additional support materials, including lecture slides, figures from the text, socket-
based programming assignments, and sample exams and programming assignments are
available through the Morgan Kaufmann website at />We suggest that you visit the page for this book every few weeks, as we will be adding
support materials and establishing links to networking-related sites on a regular basis.
And finally, as with the third edition, a set of laboratory experiments supplement
the book. These labs, developed by Professor Emad Aboelela from the University of
Massachusetts Dartmouth, use simulation to explore the behavior, scalability, and per-
formance of protocols covered in the book. Sections that discuss material covered by the
laboratory exercises are marked with the icon shown in the margin. The simulations use
the OPNET simulation toolset, which is available for free to any one using Computer
Networks in their course.
Acknowledgments
This book would not have been possible without the help of many people. We would
like to thank them for their efforts in improving the end result. Before we do so, however,

we should mention that we have done our best to correct the mistakes that the reviewers
have pointed out and to accurately describe the protocols and mechanisms that our
colleagues have explained to us. We alone are responsible for any remaining errors. If
you should find any of these, please send email to our publisher, Morgan Kaufmann,
at , and we will endeavor to correct them in future
printings of this book.
Preface xix
First, we would like to thank the many people who reviewed drafts of all or parts
of the manuscript. In addition to those who reviewed prior editions, we wish to thank
David Maltz, Bobby Bhattacharjee, and Sarvesh Kaulkarni for their thorough reviews.
Thanks also to Ric Pruss and Mike Takefman for their reviews of various sections. We
also wish to thank all those who provided feedback and input to help us decide what to
do in this edition: Tim Batten, Julio Pontes, and Kevin Mills.
Several members of the Network Systems Group at Princeton contributed ideas,
examples, corrections, data, and code to earlier editions of this book. In particular, we
would like to thank Andy Bavier, Tammo Spalink, Mike Wawrzoniak, Zuki Gottlieb,
George Tzanetakis, and Chad Mynhier. KyoungSoo Park provided valuable help on the
exercise solutions, instructor’s manual, and lecture slides. As before, we want to thank
the Defense Advanced Research Projects Agency, the National Science Foundation, Intel
Corporation, and Cisco Systems, Inc. for supporting our networking research over the
past several years. Thanks also to Cisco for providing the time for one of us to work on
the book.
This edition could not have been produced without the substantial contributions
of Mark Abbott, who crafted a great deal of new material for this book in return for not
much more than these few lines of thanks.
Finally, we would like to thank our series editor, David Clark, as well as all the
people at Morgan Kaufmann who helped shepherd us through the book-writing process.
A special thanks is due to our original sponsoring editor, Jennifer Young; our editor for
this edition, Rick Adams; our developmental editor, Rachel Roumeliotis; and to Karyn
Johnson, assistant editor on prior editions. The whole crew at MKP has been a delight

to work with over the lifetime of this book.

CONTENTS
Foreword vii
Foreword to the First Edition ix
Preface xi
1 Foundation
Problem: Building a Network 2
1.1 Applications 4
1.2 Requirements 6
1.2.1 Connectivity 7
1.2.2 Cost-Effective Resource Sharing 11
1.2.3 Support for Common Services 14
1.3 Network Architecture 19
1.3.1 Layering and Protocols 20
1.3.2 OSI Architecture 26
1.3.3 Internet Architecture 28
1.4 Implementing Network Software 30
1.4.1 Application Programming Interface (Sockets) 31
1.4.2 Example Application 33
1.4.3 Protocol Implementation Issues 37
1.5 Performance 40
1.5.1 Bandwidth and Latency 40
1.5. 2 Delay × Bandwidth Product 44
1.5.3 High-Speed Networks 46
1.5.4 Application Performance Needs 48
1.6 Summary 50
Open Issue: Ubiquitous Networking 51
Further Reading 52
Exercises 55

xxii Contents
2 Direct Link Networks
Problem: Physically Connecting Hosts 64
2.1 Hardware Building Blocks 66
2.1.1 Nodes 66
2.1.2 Links 71
2.2 Encoding (NRZ, NRZI, Manchester, 4B/5B) 79
2.3 Framing 84
2.3.1 Byte-Oriented Protocols (PPP) 84
2.3.2 Bit-Oriented Protocols (HDLC) 87
2.3.3 Clock-Based Framing (SONET) 89
2.4 Error Detection 92
2.4.1 Two-Dimensional Parity 93
2.4.2 Internet Checksum Algorithm 94
2.4.3 Cyclic Redundancy Check 96
2.5 Reliable Transmission 101
2.5.1 Stop-and-Wait 102
2.5.2 Sliding Window 105
2.5.3 Concurrent Logical Channels 115
2.6 Ethernet (802.3) 116
2.6.1 Physical Properties 116
2.6.2 Access Protocol 119
2.6.3 Experience with Ethernet 123
2.7 Rings (802.5, FDDI, RPR) 124
2.7.1 Token Ring Media Access Control 127
2.7.2 Token Ring Maintenance 129
2.7.3 FDDI 130
2.7.4 Resilient Packet Ring (802.17) 131
2.8 Wireless 133
2.8.1 Bluetooth (802.15.1) 136

2.8.2 Wi-Fi (802.11) 137
2.8.3 WiMAX (802.16) 143
2.8.4 Cell Phone Technologies 145
2.9 Summary 147
Open Issue: Sensor Networks 148
Further Reading 149
Exercises 151
3 Packet Switching
Problem: Not All Networks Are Directly Connected 166
3.1 Switching and Forwarding 168
Contents xxiii
3.1.1 Datagrams 170
3.1.2 Virtual Circuit Switching 172
3.1.3 Source Routing 179
3.2 Bridges and LAN Switches 183
3.2.1 Learning Bridges 184
3.2.2 Spanning Tree Algorithm 187
3.2.3 Broadcast and Multicast 192
3.2.4 Limitations of Bridges 193
3.3 Cell Switching (ATM) 195
3.3.1 Cells 195
3.3.2 Segmentation and Reassembly 200
3.3.3 Virtual Paths 205
3.3.4 Physical Layers for ATM 206
3.4 Implementation and Performance 208
3.4.1 Ports 210
3.4.2 Fabrics 214
3.5 Summary 218
Open Issue: The Future of Switching 219
Further Reading 219

Exercises 221
4 Internetworking
Problem: There Is More Than One Network 232
4.1 Simple Internetworking (IP) 234
4.1.1 What Is an Internetwork? 234
4.1.2 Service Model 236
4.1.3 Global Addresses 248
4.1.4 Datagram Forwarding in IP 250
4.1.5 Address Translation (ARP) 254
4.1.6 Host Configuration (DHCP) 259
4.1.7 Error Reporting (ICMP) 262
4.1.8 Virtual Networks and Tunnels 262
4.2 Routing 266
4.2.1 Network as a Graph 268
4.2.2 Distance Vector (RIP) 269
4.2.3 Link State (OSPF) 277
4.2.4 Metrics 286
4.2.5 Routing for Mobile Hosts 289
4.2.6 Router Implementation 294
4.3 Global Internet 297
xxiv Contents
4.3.1 Subnetting 299
4.3.2 Classless Routing (CIDR) 303
4.3.3 Interdomain Routing (BGP) 306
4.3.4 Routing Areas 316
4.3.5 IP Version 6 (IPv6) 318
4.4 Multicast 329
4.4.1 Multicast Addresses 331
4.4.2 Multicast Routing (DVMRP, PIM, MSDP) 332
4.5 Multiprotocol Label Switching 343

4.5.1 Destination-Based Forwarding 344
4.5.2 Explicit Routing 350
4.5.3 Virtual Private Networks and Tunnels 352
4.6 Summary 356
Open Issue: Deployment of IPv6 358
Further Reading 359
Exercises 360
5 End-to-End Protocols
Problem: Getting Processes to Communicate 380
5.1 Simple Demultiplexer (UDP) 382
5.2 Reliable Byte Stream (TCP) 384
5.2.1 End-to-End Issues 385
5.2.2 Segment Format 387
5.2.3 Connection Establishment and Termination 390
5.2.4 Sliding Window Revisited 394
5.2.5 Triggering Transmission 400
5.2.6 Adaptive Retransmission 403
5.2.7 Record Boundaries 407
5.2.8 TCP Extensions 408
5.2.9 Alternative Design Choices 410
5.3 Remote Procedure Call 411
5.3.1 RPC Fundamentals 412
5.3.2 RPC Implementations (SunRPC, DCE) 419
5.4 Transport for Real-Time Applications (RTP) 426
5.4.1 Requirements 428
5.4.2 RTP Details 429
5.4.3 Control Protocol 433
5.5 Performance 437
5.6 Summary 440
Open Issue: Application-Specific Protocols 441