BASIC CONCEPTS Time Synchronization Time Synchronization Protocols Computer Clocks Processing Time Values Correctness and Accuracy Expectations Security NTP in the Internet Parting Shots References HOW NTP WORKS General Infrastructure Requirements How NTP Represents the Time How NTP Reckons the Time How NTP Disciplines the Time How NTP Clients and Servers Associate How NTP Discovers Servers 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 References Further Reading IN THE BELLY OF THE BEAST Related Technology Terms and Notation Process Flow Packet Processing Clock Filter Algorithm Selection Algorithm Clustering Algorithm Combining Algorithm Huff-''n-Puff Filter Mitigation Rules and the Prefer Peer Poll Process Parting Shots References Further Reading CLOCK DISCIPLINE ALGORITHM Feedback Control Systems Phase and Frequency Discipline Weight Factors Poll Interval Control Popcorn and Step Control Clock State Machine Parting Shots References Further Reading NTP SUBNET CONFIGURATION Automatic Server Discovery Manual Server Discovery and Configuration Evaluating the Sources Selecting the Stratum Selecting the Number of Configured Servers Engineering Campus and Corporate Networks Engineering Home Office and Small Business Networks Hardware and Network Considerations Parting Shots References Further Reading NTP PERFORMANCE IN THE INTERNET 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 References PRIMARY SERVERS AND REFERENCE CLOCKS Driver Structure and Interface Reference Clock Drivers Further Reading KERNEL TIMEKEEPING SUPPORT System Clock Reading Algorithm Clock 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 References Further Reading CRYPTOGRAPHIC AUTHENTICATION NTP Security Model NTP Secure Groups Autokey Security Protocol Parting Shots References Further Reading IDENTITY SCHEMES X509 Certificates Private Certificate (PC) Identity Scheme Trusted Certificate (TC) Identity Scheme Schnorr (IFF) Identity Scheme Guillou-Quisquater (GQ) Identity Scheme Mu-Varadharajan (MV) Identity Scheme Parting Shots References Further Reading ANALYSIS OF ERRORS Clock Reading Errors Timestamp Errors Sawtooth Errors Maximum Error Budget Expected Error Budget Parting Shots References MODELING AND ANALYSIS OF COMPUTER CLOCKS Computer Clock Concepts Mathematical Model of the Generic Feedback Loop Synthetic Timescales and Clock Wranglers Parting Shots References Further Reading METROLOGY AND CHRONOMETRY OF THE NTP TIMESCALE Scientific Timescales Based on Astronomy and Atomic Physics Civil Timescales Based on Earth Rotation How NTP Reckons with UTC Leap Seconds On Numbering the Calendars and Days On the Julian Day Number System On Timescales, Leap Events, and the Age of Eras The NTP Era and Buddy Epoch Comparison with Other Computer Timescales Primary Frequency and Time Standards Time and Frequency Dissemination Parting Shots References 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 Reference Further Reading 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 References Further Reading BIBLIOGRAPHY INDEX.