Computer Network Time Synchronization: The Network Time Protocol on Earth and in Space, Second Edition

by Mills; David L.

• ISBN13: 9781439814635
• ISBN10: 1439814635
• Edition: 2nd
• Format: Hardcover
• Copyright: 2010-11-15
• Publisher: CRC Press

Summary

What started with the sundial has, thus far, been refined to a level of precision based on atomic resonance: Time. Our obsession with time is evident in this continued scaling down to nanosecond resolution and beyond. But this obsession is not without warrant. Precision and time synchronization are critical in many applications, such as air traffic control and stock trading, and pose complex and important challenges in modern information networks.Penned by David L. Mills, the original developer of the Network Time Protocol (NTP), Computer Network Time Synchronization: The Network Time Protocol takes a broad look at the architecture, protocols, and algorithms involved in time dissemination, distribution, and synchronization. Focused on the fourth generation of NTP, Mills' magnum opus gives an in-depth configuration and performance analysis of typical deployed NTP networks as well as a detailed error budget showing the influence of network and computer delay variations on accuracy. Mills demonstrates the algorithms used to select measurements accessed via diverse pathways to achieve the best accuracy, addresses security issues in depth, and describes the engineering principles underlying NTP architecture and timestamping exchange procedures.Opening the door to highly precise time synchronization in both public and private networks, Computer Network Time Synchronization offers in-depth analysis, theory, and practical concerns in a unified and authoritative reference.

Table of Contents

List of Illustrations	p. xv
List of Tables	p. xxi
Preface	p. xxiii
About the Author	p. xxvii
Basic Concepts	p. 1
Time Synchronization	p. 1
Time Synchronization Protocols	p. 3
Computer Clocks	p. 5
Processing Time Values	p. 7
Correctness and Accuracy Expectations	p. 8
Security	p. 10
NTP in the Internet	p. 12
Parting Shots	p. 13
References	p. 14
Further Reading	p. 14
How NTP Works	p. 15
General Infrastructure Requirements	p. 16
How NTP Represents the Time	p. 17
How NTP Reckons the Time	p. 19
How NTP Disciplines the Time	p. 21
How NTP Manages Associations	p. 22
How NTP Discovers Servers	p. 25
How NTP Deals with Stale Time Values	p. 26
How NTP Manages Network Resources	p. 27
How NTP Avoids Errors	p. 28
How NTP Performance Is Determined	p. 30
How NTP Controls Access	p. 31
How NTP Watches for Terrorists	p. 32
How NTP Clocks Are Watched	p. 33
Parting Shots	p. 34
References	p. 35
Further Reading	p. 35
In the Belly of the Beast	p. 37
Related Technology	p. 37
Terms and Notation	p. 40
Process Flow	p. 41
Peer Process	p. 43
Poll Process	p. 44
On-Wire Protocol	p. 46
Clock Filter Algorithm	p. 48
Select Algorithm	p. 51
Cluster Algorithm	p. 56
Combine Algorithm	p. 59
Mitigation Rules and the Prefer Peer	p. 60
The Prefer Peer	p. 61
Peer Classification	p. 61
Mitigation Rules	p. 62
The minsane Option	p. 63
Huff-'n-Puff Filter	p. 64
Orphan Mode	p. 65
Rate Control and the Kiss-o'-Death Packet	p. 67
Average Headway and Guard Time	p. 68
The Kiss-o'-Death Packet	p. 69
Parting Shots	p. 70
References	p. 70
Further Reading	p. 72
Clock Discipline Algorithm	p. 73
Feedback Control Systems	p. 74
Phase and Frequency Discipline	p. 76
Time and Frequency Response	p. 78
Poll Interval Control	p. 81
Popcorn and Step Control	p. 82
Clock State Machine	p. 84
Parting Shots	p. 86
References	p. 87
Further Reading	p. 87
NTP System Engineering and Configuration	p. 89
Core Engineering Principles	p. 90
Engineering Large Corporate and Campus NTP Systems	p. 92
Examples of Large Corporate NTP Systems	p. 93
Engineering Home Office and Small Business NTP Systems	p. 96
Network Considerations	p. 97
General Configuration Considerations	p. 98
Manual Server Discovery	p. 100
Automatic Server Discovery	p. 101
Broadcast/Multicast Discovery	p. 102
NTP Manycast Discovery	p. 103
NTP Pool Discovery	p. 103
Configuration Commands and Options	p. 105
Association Configuration Options (server, peer, and the Like)	p. 105
Type of Service Options (tos)	p. 107
Tinker Options (tinker)	p. 109
Parting Shots	p. 110
Further Reading	p. 110
NTP Performance in the Internet	p. 111
Performance Measurement Tools	p. 112
System Clock Latency Characteristics	p. 113
Characteristics of a Primary Server and Reference Clock	p. 114
Characteristics between Primary Servers on the Internet	p. 117
Characteristics of a Client and a Primary Server on a Fast Ethernet	p. 123
Results from an Internet Survey	p. 125
Server and Network Resource Requirements	p. 128
Parting Shots	p. 130
References	p. 130
Primary Servers and Reference Clocks	p. 131
Driver Structure and Interface	p. 132
Serial Timecode Drivers	p. 135
Generic Modem Driver	p. 137
Local Clock Driver	p. 138
PPS Interface and Driver	p. 139
Audio Drivers	p. 140
IRIG Driver	p. 142
WWV/H Driver	p. 142
CHU Driver	p. 145
References	p. 147
Kernel Timekeeping Support	p. 149
System Clock Reading Algorithm	p. 151
Kernel Discipline Algorithms	p. 153
Kernel PLL/FLL Discipline	p. 155
Kernel PPS Discipline	p. 156
Clock Adjust Algorithm	p. 158
Proof of Performance	p. 159
Kernel PLL/FLL Discipline Performance	p. 160
Kernel PPS Discipline	p. 165
Parting Shots	p. 168
References	p. 168
Further Reading	p. 168
Cryptographic Authentication	p. 169
NTP Security Model	p. 170
On the Provenance of Filestamps	p. 172
On the Naming of Things	p. 173
On Threats and Countermeasures	p. 173
NTP Secure Groups	p. 175
Autokey Security Protocol	p. 178
Session Key Operations	p. 179
X509 Certificates	p. 181
Protocol Operations	p. 182
Parting Shots	p. 183
References	p. 183
Further Reading	p. 184
Identity Schemes	p. 185
Identity Schemes	p. 186
Private Certificate Identity Scheme	p. 187
Trusted Certificate Identity Scheme	p. 188
Schnorr Identity Scheme	p. 188
Guillou-Quisquater Identity Scheme	p. 190
Mu-Varadharajan Identity Scheme	p. 192
Cryptotypes	p. 195
Parting Shots	p. 198
References	p. 198
Further Reading	p. 198
Analysis of Errors	p. 199
Clock Reading Errors	p. 200
Timestamp Errors	p. 201
Sawtooth Errors	p. 203
Peer Error Budget	p. 204
System Error Budget	p. 206
Parting Shots	p. 208
References	p. 208
Modeling and Analysis of Computer Clocks	p. 209
Computer Clock Concepts	p. 210
Mathematical Model of the Generic Feedback Loop	p. 214
Type IFLL Feedback Control Loop	p. 216
Type II Feedback Control Loop	p. 217
Synthetic Timescales and Clock Wranglers	p. 219
Parting Shots	p. 222
References	p. 222
Further Reading	p. 223
Metrology and Chronometry of the NTP Timescale	p. 225
Scientific Timescales Based on Astronomy and Atomic Physics	p. 227
UTC and the Leap Second	p. 229
The Leap Second Controversy	p. 230
How NTP Reckons with UTC Leap Seconds	p. 233
On Numbering the Calendars and Days	p. 235
On the Julian Day Number System	p. 237
On Timescales and the Age of Eras	p. 238
On NTP Era and Timestamp Calculations	p. 240
Comparison with Other Computer Timescales	p. 241
Primary Frequency and Time Standards	p. 243
Time and Frequency Coordination	p. 244
Time and Frequency Dissemination	p. 245
Shortwave Radio Services	p. 246
Long-Wave Radio Services	p. 246
Geosynchronous Operational Environmental Satellite Service	p. 247
Telephone Modem Services	p. 248
Global Positioning System	p. 248
LORAN-C Radio Navigation System	p. 249
Parting Shots	p. 252
References	p. 253
Further Reading	p. 254
NTP Reference Implementation	p. 255
NTP Packet Header	p. 256
Control Flow	p. 259
Main Program and Common Routines	p. 263
Peer Process	p. 264
System Process	p. 268
Clock Discipline Process	p. 272
Clock Adjust Process	p. 275
Poll Process	p. 276
Parting Shots	p. 277
References	p. 279
Further Reading	p. 279
Precision System Clock Architecture	p. 281
Limitations of the Art	p. 281
Precision System Clock	p. 282
Timer Oscillator	p. 283
Timestamp Counter	p. 283
Real-Time Clock	p. 284
Precision System Clock Implementation	p. 285
Precision System Clock Operations	p. 287
Principles of Precision Timestamping	p. 289
Timestamp Transposition	p. 291
Error Analysis	p. 293
Reciprocity Errors	p. 294
Transposition Errors	p. 295
Interworking Errors	p. 295
Store-and-Forward Errors	p. 296
Nonreciprocal Rate Errors	p. 297
IEEE 1588 Precision Time Protocol	p. 298
Timestamp Capture	p. 298
PTP Clock Architecture	p. 300
PTP Messages	p. 301
Best Master Clock Algorithm	p. 302
Data Set Comparison Algorithm	p. 303
PTP Time Transfer	p. 304
PTP and NTP Compared	p. 305
Have Quick, STANAG 4330, and Precise Time and Time Interval Have Quick Interfaces	p. 307
Parting Shots	p. 309
References	p. 309
NTP Interleaved Modes	p. 311
Basic/Interleaved Protocol State Machines and Flowcharts	p. 312
Basic Symmetric Mode	p. 315
Interleaved Symmetric Mode	p. 317
Interleaved Broadcast Mode	p. 319
Error Detection and Recovery	p. 322
Measured Performance with the Interleaved Modes	p. 323
Parting Shots	p. 327
Time Transfer for Space Data Links	p. 329
Orbit Mechanics	p. 330
Clock Comparisons and the Effects of General Relativity	p. 333
Time Transfer from a Planet to the Solar System Barycenter	p. 338
Time Comparisons between Clocks in Space	p. 339
Spacecraft Electronics	p. 342
Proximity-1 Protocol	p. 345
Proximity-1 Time Service	p. 346
Time Transfer Using the Electra Transceiver	p. 347
Parting Shots	p. 349
References	p. 351
Further Reading	p. 352
Time Transfer for Deep-Space Missions	p. 353
Time Transfer between Earth Stations	p. 354
Time Transfer to Earth Satellites	p. 357
Time Transfer to the Moon and Satellites of Other Planets	p. 359
Time Transfer for a Planetary Space Fleet	p. 361
Time Transfer for Deep-Space Missions	p. 367
Parting Shots	p. 372
References	p. 375
Technical History of NTP	p. 377
On the Antiquity of NTP	p. 378
On the Proliferation of NTP around the Globe	p. 381
Autonomous Authentication	p. 381
Autonomous Configuration	p. 383
Radios, We Have Radios	p. 384
Hunting the Nanoseconds	p. 385
Experimental Studies	p. 388
Theory and Algorithms	p. 389
Growing Pains	p. 391
As Time Goes By	p. 391
Parting Shots	p. 392
References	p. 393
Further Reading	p. 396
Bibliography	p. 397
Acronyms	p. 407
Index	p. 411
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