COMPUTER NETWORK TIME SYNCHRONIZATION

Transcription

1 Second Edition COMPUTER NETWORK TIME SYNCHRONIZATION The Network Time Protocol on Earth and in Space David L. Mills Up) CRC Press \V J Taylor &. Francis Group Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business

2 List of Illustrations List of Tables Preface About the Author xv xxi xxiii xxvii 1 Basic Concepts Time Synchronization Time Synchronization Protocols Computer Clocks Processing Time Values Correctness and Accuracy Expectations Security NTP in the Internet Parting Shots 13 References 14 Further Reading 14 2 How NTP Works General Infrastructure Requirements How NTP Represents the Time How NTP Reckons the Time How NTP Disciplines the Time How NTP Manages Associations How NTP Discovers Servers How NTP Deals with Stale Time Values How NTP Manages Network Resources How NTP Avoids Errors How NTP Performance Is Determined How NTP Controls Access How NTP Watches for Terrorists How NTP Clocks Are Watched Parting Shots 34 References 35 Further Reading 35 3 In the Belly of the Beast Related Technology Terms and Notation Process Flow 41 Vll

3 viii 3.4 Peer Process Poll Process On-Wire Protocol Clock Filter Algorithm Select Algorithm Cluster Algorithm Combine Algorithm Mitigation Rules and the Prefer Peer The Prefer Peer Peer Classification Mitigation Rules The minsane Option Huff-'n-Puff Filter Orphan Mode Rate Control and the Kiss-o'-Death Packet Average Headway and Guard Time The Kiss-o'-Death Packet Parting Shots 70 References 70 Further Reading 72 4 Clock Discipline Algorithm Feedback Control Systems Phase and Frequency Discipline Time and Frequency Response Poll Interval Control Popcorn and Step Control Clock State Machine Parting Shots 86 References 87 Further Reading 87 5 NTP System Engineering and Configuration Core Engineering Principles Engineering Large Corporate and Campus NTP Systems Examples of Large Corporate NTP Systems Engineering Home Office and Small Business NTP Systems Network Considerations General Configuration Considerations Manual Server Discovery Automatic Server Discovery Broadcast/Multicast Discovery NTP Manycast Discovery NTP Pool Discovery 103

4 ix 5.9 Configuration Commands and Options Association Configuration Options (server, peer, and the Like) Type of Service Options (tos) Tinker Options (tinker) Parting Shots 110 Further Reading NTP Performance in the Internet Ill 6.1 Performance Measurement Tools System Clock Latency Characteristics Characteristics of a Primary Server and Reference Clock Characteristics between Primary Servers on the Internet Characteristics of a Client and a Primary Server on a Fast Ethernet Results from an Internet Survey Server and Network Resource Requirements Parting Shots 130 References Primary Servers and Reference Clocks Driver Structure and Interface Serial Timecode Drivers Generic Modem Driver Local Clock Driver PPS Interface and Driver Audio Drivers IRIG Driver WWV/H Driver CHU Driver 145 References Kernel Timekeeping Support System Clock Reading Algorithm Kernel Discipline Algorithms Kernel PLL/FLL Discipline Kernel PPS Discipline Clock Adjust Algorithm Proof of Performance Kernel PLL/FLL Discipline Performance Kernel PPS Discipline Parting Shots 168 References 168 Further Reading 168

5 x 9 Cryptographic Authentication NTP Security Model On the Provenance of Filestamps On the Naming of Things On Threats and Countermeasures NTP Secure Groups Autokey Security Protocol Session Key Operations X509 Certificates Protocol Operations Parting Shots 183 References 183 Further Reading Identity Schemes Identity Schemes Private Certificate Identity Scheme Trusted Certificate Identity Scheme Schnorr Identity Scheme Guillou-Quisquater Identity Scheme Mu-Varadharajan Identity Scheme Cryptotypes Parting Shots 198 References 198 Further Reading Analysis of Errors Clock Reading Errors Timestamp Errors Sawtooth Errors Peer Error Budget System Error Budget Parting Shots 208 References Modeling and Analysis of Computer Clocks Computer Clock Concepts Mathematical Model of the Generic Feedback Loop Type IFLL Feedback Control Loop Type II Feedback Control Loop Synthetic Timescales and Clock Wranglers Parting Shots 222 References 222 Further Reading 223

6 xi 13 Metrology and Chronometry of the NTP Timescale Scientific Timescales Based on Astronomy and Atomic Physics UTC and the Leap Second The Leap Second Controversy How NTP Reckons with UTC Leap Seconds On Numbering the Calendars and Days On the Julian Day Number System On Timescales and the Age of Eras On NTP Era and Timestamp Calculations Comparison with Other Computer Timescales Primary Frequency and Time Standards Time and Frequency Coordination Time and Frequency Dissemination Shortwave Radio Services Long-Wave Radio Services Geosynchronous Operational Environmental Satellite Service Telephone Modem Services Global Positioning System LORAN-C Radio Navigation System Parting Shots 252 References 253 Further Reading NTP Reference Implementation NTP Packet Header Control Flow Main Program and Common Routines Peer Process System Process Clock Discipline Process Clock Adjust Process Poll Process Parting Shots 277 References 279 Further Reading Precision System Clock Architecture Limitations of the Art Precision System Clock Timer Oscillator Timestamp Counter Real-Time Clock 284

7 хп Precision System Clock Implementation Precision System Clock Operations Principles of Precision Timestamping Timestamp Transposition Error Analysis Reciprocity Errors Transposition Errors Interworking Errors Store-and-Forward Errors Nonreciprocal Rate Errors IEEE 1588 Precision Time Protocol Timestamp Capture PTP Clock Architecture PTP Messages Best Master Clock Algorithm Data Set Comparison Algorithm PTP Time Transfer PTP and NTP Compared Have Quick, STANAG 4330, and Precise Time and Time Interval Have Quick Interfaces Parting Shots 309 References NTP Interleaved Modes Basic/Interleaved Protocol State Machines and Flowcharts Basic Symmetric Mode Interleaved Symmetric Mode Interleaved Broadcast Mode Error Detection and Recovery Measured Performance with the Interleaved Modes Parting Shots Time Transfer for Space Data Links Orbit Mechanics Clock Comparisons and the Effects of General Relativity Time Transfer from a Planet to the Solar System Barycenter Time Comparisons between Clocks in Space Spacecraft Electronics Proximity-1 Protocol Proximity-1 Time Service Time Transfer Using the Electra Transceiver Parting Shots 349 References 351 Further Reading 352

8 xiii 18 Time Transfer for Deep-Space Missions Time Transfer between Earth Stations Time Transfer to Earth Satellites Time Transfer to the Moon and Satellites of Other Planets Time Transfer for a Planetary Space Fleet Time Transfer for Deep-Space Missions Parting Shots 372 References Technical History of NTP On the Antiquity of NTP On the Proliferation of NTP around the Globe Autonomous Authentication Autonomous Configuration Radios, We Have Radios Hunting the Nanoseconds Experimental Studies Theory and Algorithms Growing Pains As Time Goes By Parting Shots 392 References 393 Further Reading 396 Bibliography 397 Acronyms 407 Index 411