Engineering Internet QoS 1st Edition Sanjay Jha

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Engineering Internet QoS 1st Edition Sanjay Jha Digital
Instant Download
Author(s): Sanjay Jha, Mahbub Hassan
ISBN(s): 9781580535663, 1580535666
Edition: 1st
File Details: PDF, 1.91 MB
Year: 2002
Language: english

For a listing of recent titles in the Artech House Telecommunications Library, turn to
the back of this book.

Engineering Internet QoS
Sanjay Jha
Mahbub Hassan
Artech House
Boston • London
www.artechhouse.com

Library of Congress Cataloging-in-Publication Data
Jha, Sanjay.
Engineering Internet QoS / Sanjay Jha, Mahbub Hassan.
p. cm. — (Artech House telecommunications library)
Includes bibliographical references and index.
ISBN 1-58053-341-8 (alk. paper)
1. Internet—Evaluation. 2. Telecommunications—Traffic management. 3. Quality
control. I. Hassan, Mahbub. II. Title. III. Series.
TK5105.875.I57 J53 2002
004.6—dc21 2002074494
British Library Cataloguing in Publication Data
Jha, Sanjay
Engineering Internet QoS. — (Artech House
telecommunications library)
1. Computer engineering 2. Internet 3. Computer networks–
Quality control
I. Title II. Hassan, Mahbub
621.3'981
ISBN 1-58053-341-8
Cover design by Gary Ragaglia
© 2002 ARTECH HOUSE, INC.
685 Canton Street
Norwood, MA 02062
All rights reserved. Printed and bound in the United States of America. No part of this book
may be reproduced or utilized in any form or by any means, electronic or mechanical, in-
cluding photocopying, recording, or by any information storage and retrieval system, with-
out permission in writing from the publisher.
All terms mentioned in this book that are known to be trademarks or service marks have
been appropriately capitalized. Artech House cannot attest to the accuracy of this informa-
tion. Use of a term in this book should not be regarded as affecting the validity of any trade-
mark or service mark.
International Standard Book Number: 1-58053-341-8
Library of Congress Catalog Card Number: 2002074494
10 9 8 7 6 5 4 3 2 1

v
To my father, Krishna, my wife, Manju, and my pets, Kookaburra (Maansi)
and Possum (Pranay).
Sanjay Jha
To my son, Aaron.
Mahbub Hassan

Contents
Preface xv
Chapter 1 Introduction 1
1.1 QoS Framework 1
1.2 Video-Conferencing System 5
1.3 Overview of Audio-Video Compression Techniques 6
1.3.1 Video-Compression Standards 6
1.3.2 Audio-Compression 9
1.4 End-System Considerations 9
1.5 Operating-System Approach 10
1.6 Overview of Networking and Media Technologies 11
1.7 End-to-End QoS in the Internet 13
1.8 Supporting QoS in Best-Effort Networks 14
1.9 Application-Level Adaptation 16
1.9.1 Montgomery’s Destination Wait Method 16
1.9.2 Adaptive Audio Playout 18
1.9.3 Feedback Control Mechanism 19
1.9.4 Forward Error Correction 19
1.9.5 Interleaving 20
1.9.6 Repair at Receiver 20
1.10 Real-Time Protocol 20
1.11 Real-Time Control Protocol 22
1.11.1 Interarrival Jitter Calculation 24
1.11.2 Example: Audio Transmission in the Internet 24
1.12 Summary 26
vii

viii Contents
1.13 Review Questions 26
Chapter 2 QoS Fundamentals 31
2.1 Traffic Description 31
2.1.1 Types of Traffic Sources 31
2.1.2 Traffic Parameters 32
2.2 QoS Specification and Contract 34
2.3 QoS Signaling 34
2.4 Packet Classification 34
2.5 Resource Reservation 35
2.6 Admission Control 35
2.7 Traffic Policing 36
2.7.1 Requirements for Traffic Policing 36
2.7.2 Policing Parameters 37
2.7.3 Policing Algorithms 37
2.8 Traffic Shaping 42
2.9 Queuing and Scheduling 43
2.10 Congestion Control and Buffer Management 44
2.11 Research Directions 44
2.12 Summary 45
Chapter 3 Scheduling for QoS Management 49
3.1 Scheduling Goals 49
3.2 Scheduling Techniques 52
3.2.1 First Come First Serve 52
3.2.2 Priority Queuing 53
3.2.3 Generalized Processor Sharing 54
3.2.4 Round Robin 56
3.2.5 Weighted Round Robin 57
3.2.6 Deficit Round Robin 58
3.2.7 Weighted Fair Queuing 60
3.2.8 Virtual Clock 66
3.3 Class-Based Queuing 67
3.4 Implementation Status 69
3.5 Research Directions in Scheduling 71
3.6 Summary 73
3.8 Implementation Project 74

Contents ix
Chapter 4 TCP/IP and Queue Management 77
4.1 Internet Protocol 77
4.1.1 Datagram Forwarding 78
4.1.2 Unreliable Delivery of Datagrams 78
4.1.3 Datagram Format 78
4.2 User Datagram Protocol 81
4.3 TCP Basics 82
4.4 TCP Segment Format 82
4.5 TCP Three-Way Handshake 85
4.6 TCP Acknowledgment 86
4.7 Flow Control 86
4.8 Congestion Control 88
4.8.1 Packet Loss Detection 88
4.8.2 Retransmission Timer 89
4.8.3 RTT Estimation 89
4.8.4 Slow Start 90
4.8.5 AIMD 90
4.8.6 TCP Tahoe/Reno/Vegas 92
4.9 Queue Management 93
4.9.1 Explicit Congestion Notification 93
4.9.2 Packet Drop Schemes 94
4.9.3 Global Synchronization Problem 95
4.9.4 Random Early Detection Scheme 95
4.9.5 Weighted Random Early Detection 98
4.9.6 RED with In/Out 98
4.9.7 Problems with RED 99
4.10.1 Blue 100
4.10.2 Related Work 101
4.11 Summary 102
Chapter 5 Integrated Services Packet Network 107
5.1 Intserv Aim 108
5.2 Application Classification 108
5.2.1 Elastic Applications 108
5.2.2 Tolerant Real-Time Applications 109
5.2.3 Intolerant Real-Time Applications 109

x Contents
5.3 Intserv Service Classes 109
5.3.1 Controlled Load Service Class 110
5.3.2 Guaranteed Service Class 110
5.4 Flow Definition 111
5.5 Signaling/Flow Setup 111
5.6 Routing Protocol Independence 112
5.7 Reservation Specs 113
5.8 IS-Capable Router Components 116
5.8.1 Admission Control 116
5.8.2 Policing and Shaping 117
5.8.3 Packet Classifier 117
5.8.4 Packet Scheduler 118
5.8.5 Packet Processing 118
5.8.6 Traffic Control Implementation 118
5.9 LAN QoS and Intserv 120
5.9.1 QoS Problem in LAN 120
5.9.2 IEEE Solution for LAN QoS 120
5.9.3 Mapping of Intserv QoS to LAN QoS 124
5.10 Intserv Problems 125
5.12 Summary 128
Chapter 6 Resource Reservation Protocol 133
6.1 RSVP Features 133
6.1.1 Simplex Protocol 133
6.1.2 Receiver-Oriented Approach 134
6.1.3 Routing-Protocol Independent 134
6.1.4 Reservation Setup 134
6.1.5 Soft State Refresh 135
6.2 Reservation Merger 135
6.3 Reservation Styles 137
6.3.1 Wildcard Filter 137
6.3.2 Shared Explicit 138
6.3.3 Fixed Filter 139
6.3.4 RSVP/ns Simulation 141
6.4 RSVP Messages 143
6.4.1 PATH Messages 144

Contents xi
6.4.2 RESV Messages 145
6.4.3 Other RSVP Messages 145
6.4.4 Message Processing 146
6.5 RSVP Message Format 147
6.5.1 Session Objects 148
6.5.2 TSpec Object 148
6.5.3 AdSpec Object Class 149
6.5.4 AdSpec Functional Block 150
6.5.5 Other RSVP Objects 151
6.5.6 PATH Message Format 152
6.5.7 RESV Message Format 153
6.5.8 Controlled Load Flow Specification 154
6.5.9 Guaranteed Load Flow Specification 154
6.6 RSVP APIs 155
6.7 RSVP Problems 157
6.8 Other Resource Reservation Protocols 159
6.9 RSVP Extensions 160
6.9.1 Improvement-Related Extensions 161
6.9.2 Subnet Bandwidth Manager 161
6.9.3 New Application-Related Extensions 163
6.10 Summary 164
Chapter 7 IP Differentiated Services Network 169
7.1 Diffserv Architecture 169
7.1.1 Per-Hop Behavior 171
7.1.2 Per-Domain Behavior 171
7.1.3 Existing IPv4 ToS 172
7.1.4 Diffserv Codepoint 172
7.1.5 PHB Encoding 173
7.2 Diffserv Router 175
7.3 Premium Service 178
7.4 Experimental Evaluation of Premium Service Under Linux 179
7.5 Assured Service 184
7.6 Open Issues with Diffserv 187
7.7 Diffserv Research Directions 187
7.8 Summary 190

xii Contents
Chapter 8 Policy-Based QoS Management 195
8.1 Definition of Terminologies 195
8.2 Bandwidth Broker 196
8.3 Policy Framework 198
8.3.1 Policy Protocols 200
8.3.2 Policy Rules and Representations 201
8.3.3 Policy Database 202
8.4 Policy and RSVP 203
8.5 Bandwidth Broker Implementation 203
8.6 Internet2 and QBone 208
8.8 Summary 209
Chapter 9 ATM QoS 213
9.1 Why ATM Networks? 213
9.2 Protocol Architecture 214
9.3 Connections 215
9.3.1 Virtual Channel 216
9.3.2 Virtual Path 216
9.3.3 Permanent and Switched Virtual Circuits 216
9.4 Interfaces 217
9.5 Cell Formats 218
9.6 QoS Support 220
9.6.1 Traffic Contract 220
9.6.2 Traffic Descriptions 221
9.6.3 QoS Parameters 222
9.6.4 Service Classes 222
9.7 Adaptation Layers 224
9.8 IP-ATM Integration 227
9.8.1 ATM Deployment in IP Networks 227
9.8.2 Encapsulation of IP Datagrams into ATM Cells 228
9.9 IP-ATM QoS Mapping 232
9.9.1 Intserv over ATM 233
9.9.2 Diffserv over ATM 233
9.9.3 Performance Implications of QoS Mapping 235

Contents xiii
9.9.4 MPLS Solution 235
9.11 Summary 236
9.12 Further Reading 237
Chapter 10Multiprotocol Label Switching 241
10.1 Proprietary Protocols 241
10.2 Motivation 242
10.3 MPLS Basics 243
10.4 Conventional IP Routing 244
10.5 MPLS Approach 245
10.5.1 Label Encoding 245
10.5.2 TTL Handling 246
10.5.3 MPLS Encapsulation 246
10.5.4 Label Processing 246
10.6 Label Distribution 247
10.6.1 Sample Network 247
10.6.2 Label Binding 248
10.6.3 Label Allocation 249
10.6.4 Label Switching 250
10.7 Hierarchical Routing 252
10.8 MPLS over ATM 254
10.9 Traffic Engineering Using MPLS 256
10.9.1 Constraint Routed LSP 257
10.9.2 Path Resource Reservation Protocols 258
10.9.3 Traffic Trunk 260
10.9.4 MPLS Experimental Results 261
10.9.5 No Trunking 261
10.9.6 Two Trunks Using LSPs 262
10.10MPLS and latest developments 262
10.10.1 Diffserv over MPLS 262
10.10.2 Generalized MPLS (GMPLS) 264
10.11Summary 265
10.12Review Questions 265
Chapter 11QoS in Mobile Wireless Networks 269
11.1 Mobile Applications 269
11.2 Mobile Wireless Networks 270

xiv Contents
11.2.1 Wireless LAN 271
11.2.2 Bluetooth 272
11.2.3 Cellular Networks 273
11.2.4 Comparison of Wireless Networks 274
11.3 Mobile Services over IP Networks 274
11.3.1 Mobile IP 274
11.3.2 Cellular IP 277
11.4 Impact of Mobility on QoS 278
11.4.1 Effect of Wireless Links 278
11.4.2 Effect of Movement 279
11.4.3 Limitations of Portable Devices 279
11.5 Managing QoS in Mobile Environments 280
11.5.1 Resource Reservation 280
11.5.2 Context-Aware Handoff 282
11.5.3 Application Adaptivity 282
11.7 Summary 287
Chapter 12Future 293
12.1 Intserv over Diffserv 293
12.1.1 Motivation 293
12.1.2 Generic Framework for Intserv over Diffserv 293
12.1.3 Guaranteed Service over EF PHB 295
12.1.4 Controlled Load over AF PHB 296
12.2 QoS Routing 297
12.3 Resource Discovery and QoS 297
12.4 Virtual Private Network and QoS 298
12.5 Content Distribution Network and QoS 299
12.6 Web QoS 300
12.7 Billing and Charging for QoS 301
12.8 Final Words 302
12.9 Summary 303
12.10Review Questions 303
About the Authors 307
Index 309

Preface
Engineering Internet QoS addresses the technical issues raised by the emergence of
new types, classes, and qualities of the Internet services. The international research
community has been working for the last decade on designing solutions to the QoS
problems in the Internet. The Internet Engineering Task Force (IETF) has issued
many standards recommending architectures and protocols to build a QoS support
infrastructure for the IP networks. The volume and pace of this QoS research
and development have demanded new textbooks on this topic. Although several
books on QoS have been published in the last few years, currently no text exists
that provides a single comprehensive source for the QoS concepts, architectures,
and algorithms. Most books cover the latest developments in IETF without going
into the depth of the fundamentals that is required to provide QoS. Readers are
required to consult several reference books to gain an in-depth understanding of the
fundamental concepts to build QoS in the Internet. This makes it difficult to adopt
any of these books as a text for a course on QoS.
We have written Engineering Internet QoS to provide a comprehensive source
of knowledge in the field. We have attempted to provide sufficient depth for the ma-
jor QoS concepts and architectures. Simulation results have been presented to help
understand some of the difficult concepts. The book has several Linux/FreeBSD–
based practical examples to illustrate how QoS testbeds can be set up for experi-
mentation and future research.
xv

xvi Engineering Internet QoS
ASSUMED KNOWLEDGE
Readers would be required to have the basic knowledge of data communications
and TCP/IP protocols, with some exposure to IP routing.
AUDIENCE
The book is designed for use in a second course on networking with a prerequisite
of introductory networking or data communications. The name of the course can be
as specific as “QoS in the Internet.” The book can also be used in some existing
networking courses. Some of the possible courses for which the book can be
adopted include Advanced Computer Networks and High Performance Networks.
Graduate students will find the sections on “research direction” useful for their
literature survey in the respective fields.
Professionals working as network engineers, telecommunication and network
software developers, R&D managers, research scientists, and network administra-
tors will also find this book valuable to understanding the QoS issues and how to
implement, maintain, and deploy QoS technologies. QoS API and traffic control ex-
amples will help engineers learn how to configure a router/switch supporting QoS.
Since this book is partly based on the industry short courses the authors developed,
the book will be suitable for internal training in many telecommunication industries.
The trainees will find the knowledge acquired useful in creating new products or
setting new directions for their team.
ORGANIZATION
1. Introduction: We believe that it will be easier to understand the specific
architectures once the readers have absorbed the fundamental issues and
techniques. This chapter provides definition of the QoS problem and QoS
parameters and answers why QoS is an important problem. This is followed
by the issues in providing QoS in the Internet environment. Through an
example, we discuss issues related to providing end-to-end QoS for real-time
multimedia communications over the Internet. End system as well as network
issues are discussed. The standard protocol real-time transport protocol (RTP)
and RTCP are also discussed, with examples of how they provide features
for supporting adaptive feedback as well as jitter calculation. Readers not
familiar with the QoS area will find this chapter interesting.

Preface xvii
2. QoS Fundamentals: In order to understand various architectures for QoS
provisioning in the Internet, it is important to understand the fundamental
algorithms/techniques behind these architectures. This chapter provides an
overview of the fundamental issues such as traffic specification and nego-
tiation, admission control, resource reservation, scheduling, and congestion
control. A detailed treatment to shaping and policing has been provided in this
chapter. Highly technical details of scheduling, congestion control, and buffer
management as well as resource reservation are provided in later chapters.
Readers familiar with these basic concepts may find the specialized chapters
more useful.
3. Scheduling for QoS Management: Packet scheduling is an important build-
ing block for any QoS network. This chapter provides an in-depth treatment
of this topic. A variety of schedulers including FCFS, priority round robin,
fair queuing, and its variants are discussed in details with examples of how
they could meet the delay and bandwith requirements of flows. There is an
overview of several advanced schedulers, and current research issues are de-
scribed. We recommend this chapter to both novice and advanced readers.
4. TCP/IP and Queue Management: This chapter provides a brief refresher on
TCP and IP protocols. Another objective of this section is to provide readers
with background on how the congestion control problem is currently solved
in the best-effort Internet. Authors have included this material to minimize
cross–referencing to other books where possible. Readers familiar with these
concepts may skip this section. The later part of this chapter deals with
queue management techniques used in best effort as well as QoS-capable
networks. Algorithms, such as RED/RIO, wRED, and Blue are discussed in
detail. An overview of current research issues relating to queue management
is described in this chapter.
5. Integrated Services Packet Network: One of the earliest architectures for
QoS support within IETF is the integrated services (Intserv) model. This
chapter starts with classification and requirements of applications, followed
by description of various components of the Intserv model. Components of
an Intserv capable router are described in detail. QoS support issues in the
LAN environment as well as Intserv mapping of LAN QoS are also covered
in this chapter.
6. Resource Reservation Protocol: Although flow setup has been discussed
briefly in the context of Intserv, a separate chapter has been dedicated to the

xviii Engineering Internet QoS
resource reservation protocol (RSVP). This chapter covers details of RSVP
protocol design and demonstrates its usefulness in the Intserv environment
through examples and simulation. Resource reservation protocol is an active
research area. This chapter will help researchers and implementors learn
the issues involved in designing any new resource reservation protocol. An
overview of various RSVP extensions and related research is also provided in
this chapter.
7. IP Differentiated Services Network: This chapter describes the Diffserv
architecture and its various elements. We also describe components of a
Diffserv router. Premium and assured service are described in detail with
experimental evaluation of premium service using Linux testbed. The chapter
concludes with Diffserv problems and new research development such as per-
domain behavior.
8. Policy–Based QoS Management: Policy-based QoS management is emerg-
ing as a strong research and development area for next generation Internet. We
discuss resource allocation protocol (RAP) framework. Bandwidth broker is
considered to be the oracle that has a global view of resources within a Diff-
serv domain. This chapter also describes the intra- and interdomain protocols
used in the Internet along with the Internet2 and Qbone architectures.
9. ATM QoS: ATM network was designed to support QoS from the start.
Currently many carriers have deployed ATM switches in their backbone
network. This chapter provides an overview of ATM technology as well as
the IP/ATM integration issues. This background is essential for understanding
the next chapter on MPLS. However, readers familiar with ATM network may
skip this chapter.
10. Multiprotocol Label Switching: Multiprotocol label switching has been a
popular topic for developers and researchers in the QoS area. This chapter
begins with the motivation behind developing this new technology. A detailed
description of the MPLS protocol, label distribution protocol, and issues
related to MPLS over ATM network is provided. Finally we discuss the
traffic engineering issues, with some examples of traffic trunking in MPLS
networks.
11. QoS in Mobile Wireless Networks: Mobile wireless technology has experi-
enced the same level of growth as the Internet. A vast topic like this deserves
a separate book. We start with discussion of applications and their QoS re-
quirments in the wireless Internet. We also provide a high-level overview of

Preface xix
measures currently being proposed to address the QoS issue in the wireless
Internet.
12. Future: Besides the various architectures discussed in this book, several new
architectures are evolving in the Internet. It is impossible to cover all these
new developments in a single book. We start this chapter with a detailed
discussion of Intserv over Diffserv followed by an overview of QoS routing,
VPN and QoS, content distribution network, as well as billing and charging
for QoS. Each of these sections provides a list of key references for further
reading.
Each chapter provides a section on either future research directions or latest devel-
opments in the area. Readers keen to explore the areas further will find these sec-
tions and references very useful. We have structured chapters in a way that readers
absorb basic concepts before jumping into architectural issues. Each chapter is self-
contained. We have repeated some concepts briefly in a few chapters to make them
self-contained, providing forward/backward reference for details. This facilitates
readers to carry on with the current chapter without breaking their continuity.
ON-LINE SUPPORT
On-line support material for each chapter and presentation foils (for adopters of the
text only) will be available from the following URL:
http://www.cse.unsw.edu.au/qosbook
https://hhp.bvdep.com/artechhouse
/Default.Asp?Frame=Book.Asp&Book=1-58053-341-8
ACKNOWLEDGMENTS
First of all we would like to express our gratitude to the anyonymous reviewer for
the extensive reviews of the chapters and the comments on the book’s organization.
A number of other people helped with this book. Some part of this book came
from our joint work with Professor Raj Jain from Ohio State University. Muneyb
Minhazuddin from Avaya Communications provided helpful suggestions on Diff-
serv. Professor William Atwood from Concordia University provided suggestions

xx Engineering Internet QoS
on various aspects of this book. Our graduate students William Lau, Jahan Hassan,
Alfandika, and Monir Hossain, read some of the chapter drafts. Jim Wu provided
graphics for the Diffserv chapter. Abdul Aziz Mustafa helped with the NS simula-
tion setup. Matt Chalmers and Shaleeza Sohail provided references for billing and
charging as well as policy-based management sections. Filip Rosenbaum provided
experimental results for MPLS and helped with Linux TC examples. This book has
been influenced by authors of books, articles, and RFCs provided in the refence list
after each chapter. The MPLS chapter has been influenced by Bruce Davie’s MPLS
tutorial in Globecom’98.
We are indebted to our employer, the University of New South Wales, and
our head of school, Professor Arun Sharma, for their flexibity and encouragement,
which enabled us to write this book. We acknowledge Mark Walsh, Barbara Loven-
virth, Judi Stone, Jen Kelland, Susanne Schott and others at Artech House Publish-
ers for their wonderful support. Geoff Oakley helped with Latex formatting. Finally,
we extend our gratitude to our families for their continual support throughout the
entire project.
Sanjay Jha
Mahbub Hassan
July 2002

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CHAPTER V
THE GREAT IRON KEY
JULY was hot. Everybody said so. The sun burned the grass in the
yards till it was brown, and no rain came to make it green again. All
the men were tired; some of them were cross.
Mr. Prescott put in more electric fans. Then he played the hose to
keep the air cool, but the water supply was so low that he was
ordered to stop using the hose.
One day he had an awning put up near the gate, and sent lame
Tom Murphy, the timekeeper, out there to sit.
Tom, preferring the cool of the great door where he had always
sat, confided his trouble to Billy.
“It’s my opinion,” he said, “privately spoken to you alone, that the
super sent me out here for something besides air. It’s been my
opinion, for some time, that there’s trouble somewhere.”
“I suppose,” said Billy, assuming a business tone, “that you’re a
friend back again, aren’t you, Mr. Murphy?”
Unconsciously sitting straighter in his chair, he answered, “I’m not
altogether clear as to your meaning, William.”
“You told me yourself, Mr. Murphy,” said Billy, still speaking very
firmly, “that Mr. Prescott is a friend to every man in the mill. Aren’t
you a friend back again?”
“I am,” answered the timekeeper emphatically. “You may depend
on me in all weathers, even to sitting out here in the sun.”
“Then,” said Billy, “you and I, Mr. Murphy, are both friends, on our
honor as gentlemen—that’s what my father used to say.”
“I am,” answered Thomas Murphy.

Just then they heard the honk, honk of Mr. Prescott’s machine,
and Billy stood carefully aside for him to pass.
Mr. Prescott, who was alone, said:
“Things all right, Thomas? Jump in, William.”
Billy, surprised beyond words, obeyed.
Mr. Prescott, starting the car quickly, drove rapidly down the street.
When they reached the square, Billy said:
“Some letters, sir, to post. That’s where I was going.”
“Very well,” said Mr. Prescott, stopping the car.
“Ever in a machine before?” he asked, as Billy got in again beside
him.
“No, sir.”
“Think I’ll take you with me then; I’m chasing an order. We’re
nearly out of coke.”
They rode so fast that the air began to seem cooler. Billy, quite
willing to be silent with Mr. Prescott beside him, settled back in the
seat in blissful content.
“Know anything about coke, William?” asked Mr. Prescott,
breaking the silence, suddenly.
“No, sir, except that it’s gray, and that they burn it in the cupola.”
“Oh, yes, I remember,” said Mr. Prescott; “you’re interested in iron.
Well, then, it’s time that you knew something about coke.
“Long ago they used charcoal, that is, partly burned wood, in the
iron furnaces. That used up the forests so fast that, over in England,
the government had to limit the number of iron furnaces.
“Then they tried to use coal. That didn’t work very well. Finally
somebody found that, if the coal was partly burned, that is, made into
coke, it would require less blast, and the iron would melt more
quickly. It was a great day for iron when coke came in.”
The car sped on, and again Mr. Prescott lapsed into silence.

The country didn’t look at all like the country that Billy dreamed
about. His was green. This was brown. But there were no hot, red
bricks to look at; that was something to be thankful for, anyway.
“See anything new?” asked Mr. Prescott.
“What are they?” asked Billy, pointing to long rows of something
that looked like large beehives.
“Coke ovens; they call them beehive ovens. That overhead railway
is where they charge the ovens through the top. After the coal has
burned about two days, it is quenched with water. Then they draw it
out at the bottom as coke, and put in a new charge while the ovens
are still hot.”
After he got home that night—it was closing time when they
reached the square where Mr. Prescott left him—Billy couldn’t
remember that Mr. Prescott had said a word to him all the way back.
But Billy was happy, and rested, too.
While they were walking to the mill the next morning Uncle John
said:
“Billy, my lad, I want to give you some confidential advice. You
went out riding with the superintendent yesterday, didn’t you?”
“Yes, sir,” answered Billy.
“But you’re the office boy, just the same, this morning?”
“Sure, Uncle John,” answered Billy.
“I thought you’d be clear on that,” said Uncle John, beaming with
pride. “I thought you’d be clear on that!”
Billy began the day as an office boy, dusting and sharpening
pencils and sorting the mail.
Miss King came in, looking cool and pretty in her white office
dress, with a bunch of sweet peas in her hand.
“Beautiful, aren’t they, William?” she said holding them up in the
light. “See how the lavender ones have pink in them, and the pink
have white, and the white are just tinted with pink, so they all blend

together. I always pick some leaves, too; they’re such a soft, cool
green.”
“Do you suppose,” asked Billy, “that they’d grow in a yard—just a
common yard?”
“These grew in our back yard,” answered Miss King. “I’ll give you
some seed next year.”
At that moment Mr. Prescott came in with a telegram in his hand.
“Have to catch the nine-forty express,” he said. “Can’t get back for
three days, anyway. Open those letters, William.”
Out came Billy’s knife, and he opened letters while Mr. Prescott
dictated to Miss King.
“Don’t,” said Mr. Prescott, seizing his hat, “let anybody know that I
have gone if you can help it. Don’t tell them how long I shall be gone.
You and William must look after everything.”
Then off he went, leaving Miss King and Billy looking at each other
in dismay.
“Well,” said Miss King, after a moment, “we don’t know where he
has gone. So we can’t tell anybody that. And we don’t know when he
is coming back.
“It isn’t very likely,” she added, with a reassuring smile, “that
anything will happen while he is gone.”
Billy, who had never forgotten about keeping his ears open,
thought Miss King said “very” as if she weren’t quite sure about
something. So he said:
“I’ll stay in here with you as much as I can.”
“Thank you,” said Miss King, smiling.
“There’s nothing to do, anyway,” she went on, half to herself,
“except to do things as they come along. So we’ll do that, William.
“Please get me some water for the flowers.”
Then she opened the typewriter and began to write very fast.

The day went on very much like other days. The mill seemed
almost to be running itself.
When they were leaving the office that night Miss King said
cheerfully:
“We’ve had a very pleasant day, haven’t we, William?”
“Seems to me I haven’t worked so hard as usual,” answered Billy.
The next day when Billy came back from the bank, soon after the
noon whistle had blown, lame Tom’s chair under the canopy by the
gate was empty.
Billy, hurrying on to the main building, found that Tom’s chair by
the great door was empty, too.
As he stepped inside, Tom appeared from behind the door.
When he saw Billy an expression of relief came into his face.
“I’m glad to see you, William,” he said. “Stand in the door a minute
and pretend I’m not talking to you.”
Billy, wondering what could have happened, turned his back on
Tom, and waited.
“William,” said Tom, in an almost sepulchral tone, “the great key is
gone.”
Billy nearly jumped out the door. But, remembering that he was on
duty to look after things, he said:
“You watch while I try to find it.”
Even Billy’s young eyes could not find the key. He searched till he
was sure, then he said:
“I’ll look again, Mr. Murphy, after you go out to the gate.”
The key was one of Mr. Prescott’s special treasures, for it was the
very one that his grandfather had when he first built the mill. Several
times the door had been almost made over, but the key had never
been changed.

It was an iron key—three times as long as Billy’s longest finger,
with a bow in which three of his fingers and almost a fourth could lie
side by side, and its bit was more than half as long as his thumb. It
was so large that Mr. Prescott sometimes called lame Tom “the
keeper of the great key.”
Gone it was. Billy hunted till he was sure of that. He wanted to tell
Miss King about it, but he could not stop to tell her then, for he had to
distribute the orders for the afternoon.
Here and there he went. Last of all he had to go into the foundry.
He was half-way down the room before he realized that he was on
the side where he must pass the man with the fierce eyes and the
coal black hair. Determined this time to be brave, he went steadily
on.
The man was standing still, bending over his drag, his shock of
unkempt hair hanging down over his eyes. He was so intent on his
work that Billy, so nearly past that he felt quite safe, looked down
curiously to see what pattern the man was using.
There, all by itself, in the bottom of the box, lay the great iron key.

CHAPTER VI
A SURPRISE OR TWO
THE sight of the key did something more than to make Billy’s eyes
open very wide; it struck to his legs. They grew so heavy that, for a
minute, he couldn’t lift them at all. But he kept on trying, and finally
succeeded in pulling up first one, and then the other, and in starting
them both. Then they wanted to move fast, and he had hard work to
slow them down to simply a quick walk. At last he reached the door,
and hurried across the yard and down the corridor to the office.
When he opened the door, something struck to his feet, and fairly
glued them to the threshold.
There at his desk, writing away hard, sat Mr. Prescott.
Billy’s blue eyes, large from seeing the key, grew still larger, so
that, when Mr. Prescott finally looked up, he saw quite a different boy
from the Billy whom he had left only the day before.
“Well, William,” he said, as he put down his pen, “having obeyed to
the letter—I might say to the period—my injunction to keep your lips
shut, suppose you open them.”
Billy’s tongue seemed to be fastened to the roof of his mouth
tighter than his feet were to the floor, and he couldn’t seem to
unfasten it.
“Perhaps,” continued Mr. Prescott, “it might be as well, just at this
point, for me to inform you that surprise is one of the persistent
elements of business. I met another telegram, so you meet me.
What has happened?”
When Billy finally reached the desk and began to tell him about the
key, Mr. Prescott whirled around in his chair and put his right thumb
into the right armhole of his vest.

Before Billy had finished, though his tongue, having started, went
very fast, Mr. Prescott put his other thumb in his other armhole, and
leaned back in his chair till his shoulders seemed almost to fill the
space between the desk and the railing.
“Well,” he said, when Billy had finished, “as you are the one in
possession of the original facts, what do you think had better be
done?”
If Mr. Prescott had only known it, Billy didn’t like him very well
when he talked that way. But of course nobody can like anybody
every minute of the time; for even a best hero is more than likely to
have disagreeable spots. Billy’s father had told him that, and Billy
was very much like his father in the way he had of forgetting
disagreeables pretty soon after they happened. Just that minute,
anyway, his whole mind was on that great iron key.
Besides, when Mr. Prescott talked that way, he always hit the
man-side of Billy. Possibly Mr. Prescott knew that.
“I think, sir,” answered Billy, almost before he knew what he was
saying, “that I can get the key.”
“Oh, you do, do you?” said Mr. Prescott. “Will you be so kind as to
tell me about what time to-day you will deliver it?”
Billy looked at the clock.
Miss King’s keys kept right on—clickety-clickety-click.
Billy changed his weight to his other foot before he answered:
“About four o’clock, sir.”
Mr. Prescott looked at the clock, then he took up his pen, saying:
“It is now nearly half-past three. It would be a pity, in such an
important matter, for you to fail for lack of time to work out any little
theory that you happen to have originated. Suppose we make it half-
past four o’clock.”
As Billy started for the door Mr. Prescott added:

“Having opened your lips, you may close them again, a little tighter
than before. Understand?”
“Yes, sir,” answered Billy.
“Mind,” called Mr. Prescott, when Billy had almost closed the door,
“you are to return at half-past four, key or no key.”
“Sure, sir,” answered Billy.
Things don’t always look the same on both sides of a door. Billy
found that out as soon as he was alone in the corridor. But Billy had
a theory, though Mr. Prescott may have thought that he was joking,
and it was built on so firm a foundation that William Wallace offered,
at once, to help him work it out.
Billy hadn’t visited Uncle John that day in the foundry simply for
nothing. He had it all figured out in his mind that, as soon as the
black-haired man had finished using the key for a pattern, he would
put it back in the door; and Billy had said four o’clock because that
was about the time when the molds were supposed to be ready.
When a man knew as much about molding as Mr. Prescott did, it
did seem as if he might have figured that out himself.
Billy looked around for a place where he could hide to watch the
door. There wasn’t anybody in sight, so he took plenty of time to
decide.
Half-way down the corridor, on the right hand side, was a small
closet that had been built up on the floor, by itself, so that Mr.
Prescott could have a place to keep his motor clothes.
Billy went into that, and tried, by leaving the door part way open, to
fix a crack through which he could watch the door. Finding that the
crack was too far out of range, he started down the corridor to find
another place.
He had just about decided to try hiding behind the tool room when
he heard a step, and, looking up, saw Thomas Murphy, the
timekeeper.

“It’s a great relief, William,” said Tom, “to see a friend like you.
Does the super know about the key?”
Billy looked at Tom, and Tom looked at Billy. Bad as Tom felt, Billy
felt three times worse. Billy had three things on his mind: first of all,
he mustn’t tell a lie; then, he must keep the secret; and, if Tom
Murphy stayed by that door, the man wouldn’t bring back the key.
Billy and William Wallace both thought as fast as they could. Billy
got hold of an idea first. Perhaps by asking Tom a question he could
throw him off the track, and could keep from telling a lie.
So he said: “Had you made up your mind, Mr. Murphy, when it
would be best to tell him?”
“No, William,” answered Tom Murphy, in a hopeless tone, “I hadn’t.
I’ve turned that thing over and over in my mind, and I’ve turned it
inside out; and all the answer that I can get to it is that there’ll be no
Tom Murphy any more a-keepin’ time at Prescott mill.”
“But you didn’t lose the key, Mr. Murphy,” said Billy, very
sympathetically, now that his first danger was over.
“That I didn’t,” said Tom Murphy. “It’s been a rule and a regulation
that that key was to stay in that door from morning to night. That key
ought not to have been left in that door.”
“No,” said Billy, “excepting that everybody knows how much Mr.
Prescott thinks of that key.”
“That’s just it,” said Thomas Murphy, pulling his old chair out from
behind the door, and sinking into it with a sigh of relief.
“What would you,” he asked as he stretched out his lame leg, and
clasped his hands across his chest, “what would you advise, as a
friend? Don’t leave me, William,” he exclaimed, as Billy stepped
outside.
“I won’t,” said Billy, stepping forward far enough to see the clock.
Fifteen minutes gone! Where had fifteen minutes gone?
“Do you think, William,” asked Thomas Murphy, as Billy went back
to him, “that, if the super never finds that key, there will be any

Thomas Murphy any more a-keepin’ time at Prescott mill?”
“You know,” said Billy, “that Mr. Prescott is a friend to everybody. I
think,” he added slowly, because he was trying to keep still and at
the same time to be wise, “I think he would be—more of—a friend—
to a man—than to a key.”
“His grandfather’s key?” said Tom solemnly.
“His grandfather’s key,” repeated Billy, backing toward the door,
and stepping out.
Five minutes of four!
Looking over at the foundry, Billy saw a man with shaggy black
hair who, with his right hand pressed close against his side, was
stepping back into the foundry door!
Billy himself stepped quickly back.
“William,” said Thomas Murphy, “you seem to be unusually
oneasy.”
“It’s a very warm day,” said Billy.
“If it seems hot to you in here,” said Thomas Murphy, settling still
further back in his chair, “what do you think it has been to me a-sittin’
out under that canopy in the sun?”
Billy grew desperate. “Mr. Murphy,” he said, “it seems to me—do
you think, Mr. Murphy—I mean—don’t you think that Mr. Prescott
expects you are sitting out there now?”
“That may be,” answered Thomas Murphy.
“Don’t you think,” said Billy, growing more and more desperate,
“that it would be a good plan for us to go out there together?”
“Sometimes,” said Thomas Murphy, in an injured tone, “a man’s
best friends can make things very hard for him.”
“Can I help you to get up?” asked Billy, going up to Thomas
Murphy, and putting his hand on his arm.

“No, William,” said Thomas Murphy, moving his arm with more
decision than was really necessary. “Thomas Murphy is still able to
rise without the assistance of a—a friend.”
Slowly Thomas Murphy drew himself from the depths of the chair.
Billy, backing out the great door, saw the clock.
Ten minutes more gone!
“Hurry up!” said William Wallace. “Hurry up!”
“I tell you, Mr. Murphy,” said Billy in his most friendly tone, “I’ll go
out under the canopy. Then, if Mr. Prescott does come out, he’ll see
that there’s somebody at the gate.”
“Very well,” said Thomas Murphy, lowering his lame leg carefully
down the step. “Very well.”
Billy, glad of a chance to work off his feelings, ran out to the gate
as fast as he could.
Slowly, very slowly, Thomas Murphy came across the yard.
Billy, that he might not seem to be watching, stood with his back to
the mill.
About the time that he thought Thomas Murphy would reach the
gate, he heard a sudden exclamation. Turning around, he saw
Thomas Murphy, timekeeper of Prescott mill, lying flat on his face.
Quarter-past four stood the hands of the clock. Never in his life
had Billy seen them move so fast at that time of the day.
Hurrying back he asked, “Can I help you, Mr. Murphy?”
“Thank you, William,” answered Thomas Murphy, holding out his
hand for help. “A friend in need is a friend indeed.”
As Billy bent over to help Thomas Murphy, he saw something that,
for a moment, made him so excited that he couldn’t have told
whether he was standing on his head or his heels.
A black-haired man was creeping along the wall toward the door of
the mill!

When he was sure that he was standing on his heels, Billy looked
at the clock.
Seven minutes left!
He helped Thomas Murphy to his chair. He even took time to say,
“Mr. Murphy, there are some things that I have been wanting to ask
you about iron.”
“Anything,” said Thomas Murphy, safe in his chair, “anything that I
know is at your service, William.”
Then Billy said, “Mr. Prescott told me to come back at half-past
four.”
“I should say,” remarked Thomas Murphy, “that you’ll have to
hurry, William. Near as I can see the hands of that clock, it’s hard on
to that now.”
Billy did hurry, and soon had the key safe in his hands.
As he went quickly down the corridor, William Wallace gave him
some special advice:
“Don’t explain. Business is business. Just deliver the key.”
When Billy went into the office, Mr. Prescott glanced at the clock.
“Punctuality, William,” he said, “is a desirable thing in business.”
He took the key just as if he had been expecting it.
“Thank you, William,” he said.
Then, seeming to forget Billy, he began to look the key over, stem,
bit, and bow, touching it here and there, and holding it carefully, as if
it were something that he valued very much.
Realizing, at last, that Billy was waiting, he said:
“Surprise, as I was saying, is one of the elements that must be
reckoned with in business.”
When he said that, he used his firm, business tone.
But his voice was very gentle as he looked straight into Billy’s
eyes, and added:

“This time, William, the surprise is mine.”

CHAPTER VII
IRON CUTS IRON
ABOUT the middle of the next forenoon, as Billy was going through
the gate, Thomas Murphy leaned forward confidentially, and said:
“William, that key was in that door when I went to lock it last night.”
“Yes,” said Billy, hurrying on, “I saw it there when I went home.”
Billy didn’t care to discuss the matter.
The truth was that he thought it very strange that Mr. Prescott
should have put the key right back in the lock. Business seemed to
him to have some queer places in it.
But it had pleasant places, too, for, when Billy came back, he met
Mr. Prescott, just starting on his trip around the mill.
“William,” he said, “when a boy makes practical use of a visit to a
foundry, I think it would be a good idea for him to go over a mill, don’t
you?”
That was a long speech for Mr. Prescott. There wasn’t any time
lost, however, for Billy didn’t answer. He didn’t have to, because his
face told, right away, what he thought about it.
Miss King, looking up, nodded and smiled.
Off they went: tall, broad man; boy that was growing taller and
slenderer every day.
Billy threw back his shoulders, and drew a long, deep breath. Part
of it was satisfaction; the rest was a desire to be strong and broad
like Mr. Prescott.
“That,” said Mr. Prescott, as they passed a huge drum which was
turning over and over and making a great noise, “is a rattler. There’s

some sand left on castings after molding. Put small ones in there
with pieces of wood. Rub each other off.”
Mr. Prescott went on, seeming to forget Billy, as he spoke here
and there to his men.
Billy followed close, for he knew that Mr. Prescott was likely, any
moment, to spring a question on him.
They were half-way over the mill before Mr. Prescott spoke again.
Then, stopping suddenly before a large lathe, he said:
“John Bradford makes our best beds and slides. See him?” he
asked, turning to Billy.
“He was making something long,” answered Billy.
“We make lathes,” said Mr. Prescott. “Good ones; all kinds.”
In the next room he stopped again.
“Different kinds of iron,” he said. “Some much harder than others,
like tool steel. Iron cuts iron. That’s a planing machine: automatic
plane cuts any thickness.”
Billy stopped beside the mighty planer, moving over the large
casting as easily as if the iron had been wood and the fierce chisel
only a carpenter’s plane.
They went on a little further, then Mr. Prescott turned suddenly.
“William,” he asked, “how long is an inch?”
He certainly had sprung it on Billy, but Billy’s spring worked too.
“About down to there,” he answered, marking his left forefinger off
with his right. “No,” he said, moving his mark up a little higher, “about
there.”
“You were nearer right the first time,” said Mr. Prescott. “Now,
listen to me. Iron can cut iron to within a fraction of a thousandth of
an inch.”
Billy’s eyes opened till they showed almost twice as much white as
blue.

“Automatic index registers. Man watches index.
“Look at that,” he said a moment later. “See that machine cutting a
screw.”
That seemed to be something that especially interested Mr.
Prescott, for he stood a moment to watch the tool that was cutting
into the round bar of iron, making, in even and regular grooves, a
huge screw. Automatically, too, there came down on it a steady
stream of oil.
“Why’s that?” asked Billy.
“The oil keeps the iron from becoming too hot,” answered Mr.
Prescott. “Heat expands iron. If we didn’t keep it cool, the screw
wouldn’t be the right size when it is done.
“Cold naturally works the other way. Ever hear about the iron
bridge where the parts wouldn’t quite come together, so they put ice
on to do the job?” he asked, but he kept right on, without waiting for
Billy to answer.
Billy saw other machines boring holes and rounding corners. It
seemed as if iron could cut iron into any shape that anybody wanted.
Then there were men polishing and polishing, until they could fairly
see their faces in the iron. Billy could hardly believe that the gray iron
of the foundry could ever have become such silver-shining iron.
Still Mr. Prescott kept on, Billy close behind.
“This,” said Mr. Prescott, stopping in a room almost at the end of
the mill, “is the assembly room. Here is where the machines are put
together.”

THERE WERE MEN POLISHING AND POLISHING
“Over there,” he said, pointing across the room, “they are putting a
lathe together. There will be between sixty and seventy pieces in it
when it is done. See, they have arranged all the parts.”
Billy looked wonderingly at the great base and slide, and then at
the rods and screws and handles and nuts. He didn’t see how

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