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

Contents......Page 8
List of Illustrations......Page 16
List of Tables......Page 22
Preface......Page 24
About the Author......Page 28
1.1 Time Synchronization......Page 30
1.2 Time Synchronization Protocols......Page 32
1.3 Computer Clocks......Page 34
1.4 Processing Time Values......Page 36
1.5 Correctness and Accuracy Expectations......Page 37
1.6 Security......Page 39
1.7 NTP in the Internet......Page 41
1.8 Parting Shots......Page 42
Further Reading......Page 43
2. How NTP Works......Page 44
2.1 General Infrastructure Requirements......Page 45
2.2 How NTP Represents the Time......Page 46
2.3 How NTP Reckons the Time......Page 48
2.4 How NTP Disciplines the Time......Page 50
2.5 How NTP Manages Associations......Page 51
2.6 How NTP Discovers Servers......Page 54
2.7 How NTP Deals with Stale Time Values......Page 55
2.8 How NTP Manages Network Resources......Page 56
2.9 How NTP Avoids Errors......Page 57
2.10 How NTP Performance Is Determined......Page 59
2.11 How NTP Controls Access......Page 60
2.12 How NTP Watches for Terrorists......Page 61
2.13 How NTP Clocks Are Watched......Page 62
2.14 Parting Shots......Page 63
Further Reading......Page 64
3.1 Related Technology......Page 66
3.2 Terms and Notation......Page 69
3.3 Process Flow......Page 70
3.4 Peer Process......Page 72
3.5 Poll Process......Page 73
3.6 On-Wire Protocol......Page 75
3.7 Clock Filter Algorithm......Page 77
3.8 Select Algorithm......Page 80
3.9 Cluster Algorithm......Page 85
3.10 Combine Algorithm......Page 88
3.11 Mitigation Rules and the Prefer Peer......Page 89
3.11.2 Peer Classification......Page 90
3.11.3 Mitigation Rules......Page 91
3.11.4 The minsane Option......Page 92
3.12 Huff-\'n-Puff Filter......Page 93
3.13 Orphan Mode......Page 94
3.14 Rate Control and the Kiss-o\'-Death Packet......Page 96
3.14.1 Average Headway and Guard Time......Page 97
3.14.2 The Kiss-o\'-Death Packet......Page 98
References......Page 99
Further Reading......Page 101
4. Clock Discipline Algorithm......Page 102
4.1 Feedback Control Systems......Page 103
4.2 Phase and Frequency Discipline......Page 105
4.3 Time and Frequency Response......Page 107
4.4 Poll Interval Control......Page 110
4.5 Popcorn and Step Control......Page 111
4.6 Clock State Machine......Page 113
4.7 Parting Shots......Page 115
Further Reading......Page 116
5. NTP System Engineering and Configuration......Page 118
5.1 Core Engineering Principles......Page 119
5.2 Engineering Large Corporate and Campus NTP Systems......Page 121
5.3 Examples of Large Corporate NTP Systems......Page 122
5.4 Engineering Home Office and Small Business NTP Systems......Page 125
5.5 Network Considerations......Page 126
5.6 General Configuration Considerations......Page 127
5.7 Manual Server Discovery......Page 129
5.8 Automatic Server Discovery......Page 130
5.8.1 Broadcast/Multicast Discovery......Page 131
5.8.3 NTP Pool Discovery......Page 132
5.9.1 Association Configuration Options (server, peer, and the Like)......Page 134
5.9.2 Type of Service Options (tos)......Page 136
5.9.3 Tinker Options (tinker)......Page 138
Further Reading......Page 139
6. NTP Performance in the Internet......Page 140
6.1 Performance Measurement Tools......Page 141
6.2 System Clock Latency Characteristics......Page 142
6.3 Characteristics of a Primary Server and Reference Clock......Page 143
6.4 Characteristics between Primary Servers on the Internet......Page 146
6.5 Characteristics of a Client and a Primary Server on a Fast Ethernet......Page 152
6.6 Results from an Internet Survey......Page 154
6.7 Server and Network Resource Requirements......Page 157
References......Page 159
7. Primary Servers and Reference Clocks......Page 160
7.1 Driver Structure and Interface......Page 161
7.2 Serial Timecode Drivers......Page 164
7.3 Generic Modem Driver......Page 166
7.4 Local Clock Driver......Page 167
7.5 PPS Interface and Driver......Page 168
7.6 Audio Drivers......Page 169
7.6.2 WWV/H Driver......Page 171
7.6.3 CHU Driver......Page 174
References......Page 176
8. Kernel Timekeeping Support......Page 178
8.1 System Clock Reading Algorithm......Page 180
8.2 Kernel Discipline Algorithms......Page 182
8.3 Kernel PLL/FLL Discipline......Page 184
8.4 Kernel PPS Discipline......Page 185
8.5 Clock Adjust Algorithm......Page 187
8.6 Proof of Performance......Page 188
8.7 Kernel PLL/FLL Discipline Performance......Page 189
8.8 Kernel PPS Discipline......Page 194
Further Reading......Page 197
9. Cryptographic Authentication......Page 198
9.1 NTP Security Model......Page 199
9.1.1 On the Provenance of Filestamps......Page 201
9.1.3 On Threats and Countermeasures......Page 202
9.2 NTP Secure Groups......Page 204
9.3 Autokey Security Protocol......Page 207
9.3.1 Session Key Operations......Page 208
9.3.2 X509 Certificates......Page 210
9.3.3 Protocol Operations......Page 211
References......Page 212
Further Reading......Page 213
10. Identity Schemes......Page 214
10.1 Identity Schemes......Page 215
10.1.1 Private Certificate Identity Scheme......Page 216
10.1.3 Schnorr Identity Scheme......Page 217
10.1.4 Guillou-Quisquater Identity Scheme......Page 219
10.1.5 Mu–Varadharajan Identity Scheme......Page 221
10.2 Cryptotypes......Page 224
Further Reading......Page 227
11. Analysis of Errors......Page 228
11.1 Clock Reading Errors......Page 229
11.2 Timestamp Errors......Page 230
11.3 Sawtooth Errors......Page 232
11.4 Peer Error Budget......Page 233
11.5 System Error Budget......Page 235
References......Page 237
12. Modeling and Analysis of Computer Clocks......Page 238
12.1 Computer Clock Concepts......Page 239
12.2 Mathematical Model of the Generic Feedback Loop......Page 243
12.2.1 Type I FLL Feedback Control Loop......Page 245
12.2.2 Type II Feedback Control Loop......Page 246
12.3 Synthetic Timescales and Clock Wranglers......Page 248
References......Page 251
Further Reading......Page 252
13. Metrology and Chronometry of the NTP Timescale......Page 254
13.1 Scientific Timescales Based on Astronomy and Atomic Physics......Page 256
13.2 UTC and the Leap Second......Page 258
13.3 The Leap Second Controversy......Page 259
13.4 How NTP Reckons with UTC Leap Seconds......Page 262
13.5 On Numbering the Calendars and Days......Page 264
13.6 On the Julian Day Number System......Page 266
13.7 On Timescales and the Age of Eras......Page 267
13.8 On NTP Era and Timestamp Calculations......Page 269
13.9 Comparison with Other Computer Timescales......Page 270
13.10 Primary Frequency and Time Standards......Page 272
13.11 Time and Frequency Coordination......Page 273
13.12 Time and Frequency Dissemination......Page 274
13.12.2 Long-Wave Radio Services......Page 275
13.12.3 Geosynchronous Operational Environmental Satellite Service......Page 276
13.12.5 Global Positioning System......Page 277
13.12.6 LORAN-C Radio Navigation System......Page 278
13.13 Parting Shots......Page 281
References......Page 282
Further Reading......Page 283
14. NTP Reference Implementation......Page 284
14.1 NTP Packet Header......Page 285
14.2 Control Flow......Page 288
14.3 Main Program and Common Routines......Page 292
14.4 Peer Process......Page 293
14.5 System Process......Page 297
14.6 Clock Discipline Process......Page 301
14.7 Clock Adjust Process......Page 304
14.8 Poll Process......Page 305
14.9 Parting Shots......Page 306
Further Reading......Page 308
15.1 Limitations of the Art......Page 310
15.2 Precision System Clock......Page 311
15.2.2 Timestamp Counter......Page 312
15.2.3 Real-Time Clock......Page 313
15.2.4 Precision System Clock Implementation......Page 314
15.2.5 Precision System Clock Operations......Page 316
15.3 Principles of Precision Timestamping......Page 318
15.3.1 Timestamp Transposition......Page 320
15.3.2 Error Analysis......Page 322
15.4.1 Timestamp Capture......Page 327
15.4.2 PTP Clock Architecture......Page 329
15.4.3 PTP Messages......Page 330
15.4.4 Best Master Clock Algorithm......Page 331
15.4.5 Data Set Comparison Algorithm......Page 332
15.4.6 PTP Time Transfer......Page 333
15.4.7 PTP and NTP Compared......Page 334
15.5 Have Quick, STANAG 4330, and Precise Time and Time Interval Have Quick Interfaces......Page 336
References......Page 338
16. NTP Interleaved Modes......Page 340
16.1 Basic/Interleaved Protocol State Machines and Flowcharts......Page 341
16.2 Basic Symmetric Mode......Page 344
16.3 Interleaved Symmetric Mode......Page 346
16.4 Interleaved Broadcast Mode......Page 348
16.5 Error Detection and Recovery......Page 351
16.6 Measured Performance with the Interleaved Modes......Page 352
16.7 Parting Shots......Page 356
17. Time Transfer for Space Data Links......Page 358
17.1 Orbit Mechanics......Page 359
17.2 Clock Comparisons and the Effects of General Relativity......Page 362
17.3 Time Transfer from a Planet to the Solar System Barycenter......Page 367
17.4 Time Comparisons between Clocks in Space......Page 368
17.5 Spacecraft Electronics......Page 371
17.6 Proximity-1 Protocol......Page 374
17.7 Proximity-1 Time Service......Page 375
17.8 Time Transfer Using the Electra Transceiver......Page 376
17.9 Parting Shots......Page 378
References......Page 380
Further Reading......Page 381
18. Time Transfer for Deep-Space Missions......Page 382
18.1 Time Transfer between Earth Stations......Page 383
18.2 Time Transfer to Earth Satellites......Page 386
18.3 Time Transfer to the Moon and Satellites of Other Planets......Page 388
18.4 Time Transfer for a Planetary Space Fleet......Page 390
18.5 Time Transfer for Deep-Space Missions......Page 396
18.6 Parting Shots......Page 401
References......Page 404
19. Technical History of NTP......Page 406
19.1 On the Antiquity of NTP......Page 407
19.3 Autonomous Authentication......Page 410
19.4 Autonomous Configuration......Page 412
19.5 Radios, We Have Radios......Page 413
19.6 Hunting the Nanoseconds......Page 414
19.7 Experimental Studies......Page 417
19.8 Theory and Algorithms......Page 418
19.10 As Time Goes By......Page 420
19.11 Parting Shots......Page 421
References......Page 422
Further Reading......Page 425
Bibliography......Page 426
Acronyms......Page 436