RFC 1059 Network Time Protocol July 1988 3.3. Modes of Operation 21 3.4. Event Processing 22 3.4.1. Timeout Procedure 23 3.4.2. Receive Procedure 24 3.4.3. Update Procedure 27 3.4.4. Initialization Procedures 29 4. Filtering and Selection Algorithms 29 4.1. Clock Filter Algorithm 29 4.2 Clock Selection Algorithm 30 4.3. Variable-Rate Polling 32 5. Logical Clocks 33 5.1. Uniform Phase Adjustments 35 5.2. Nonuniform Phase Adjustments 36 5.3. Maintaining Date and Time 37 5.4. Calculating Estimates 37 6. References 40 Appendices Appendix A. UDP Header Format 43 Appendix B. NTP Data Format 44 Appendix C. Timeteller Experiments 47 Appendix D. Evaluation of Filtering Algorithms 49 Appendix E. NTP Synchronization Networks 56 List of Figures Figure 2.1. Implementation Model 8 Figure 3.1. Calculating Delay and Offset 26 Figure 5.1. Clock Registers 34 Figure D.1. Calculating Delay and Offset 50 Figure E.1. Primary Service Network 57 List of Tables Table 2.1. Dates of Leap-Second Insertion 11 Table 3.1. System Variables 14 Table 3.2. Peer Variables 14 Table 3.3. Packet Variables 15 Table 3.4. Parameters 15 Table 4.1. Outlyer Selection Procedure 32 Table 5.1. Clock Parameters 35 Table C.1. Distribution Functions 47 Table D.1. Delay and Offset Measurements (UMD) 52 Table D.2.a Delay and Offset Measurements (UDEL) 52 Table D.2.b Offset Measurements (UDEL) 53 Table D.3. Minimum Filter (UMD - NCAR) 54 Table D.4. Median Filter (UMD - NCAR) 54 Table D.5. Minimum Filter (UDEL - NCAR) 55 Table E.1. Primary Servers 56 Mills