Network Time Protocol (Version 2) Specification and Implementation

By Mills, David L.

Book Id: WPLBN0000693698
Format Type: PDF eBook:
File Size: 0.1 MB
Reproduction Date: 2005

Title:	Network Time Protocol (Version 2) Specification and Implementation
Author:	Mills, David L.
Volume:
Language:	English
Subject:	Math, Technology, Fine Arts
Collections:	Technical eBooks and Manuals Collection, Technical eBooks Collection
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Citation APA MLA Chicago L. Mill, B. D. (n.d.). Network Time Protocol (Version 2) Specification and Implementation. Retrieved from http://gutenberg.cc/

Description
Technical Reference Publication

Excerpt
Introduction: This document constitutes a formal specification of the Network Time Protocol (NTP), which is used to synchronize timekeeping among a set of distributed time servers and clients. It defines the architectures, algorithms, entities and protocols used by NTP and is intended primarily for implementors. A companion document [44] summarizes the requirements, analytical models, algorithmic analysis and performance under typical Internet conditions. NTP was first described in RFC-958 [30], but has evolved in significant ways, culminating in the most recent NTP Version 1 described in RFC-1059 [42]. It is built on the Internet Protocol (IP) [14] and User Datagram Protocol (UDP) [9], which provide a connectionless transport mechanism; however, it is readily adaptable to other protocol suites. NTP is evolved from the Time Protocol [19] and the ICMP Timestamp message [15], but is specifically designed to maintain accuracy and robustness, even when used over typical Internet paths involving multiple gateways, highly dispersive delays and unreliable nets.

Table of Contents
Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1. Related Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. System Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Implementation Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Network Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. The NTP Timescale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.4. The NTP Calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.5. Time and Frequency Dissemination . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3. Network Time Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.2. State Variables and Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2.1. Common Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2.2. System Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2.3. Peer Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.2.4. Packet Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.5. Clock Filter Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.6. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.3. Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.4. Event Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.4.1. Transmit Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.4.2. Receive Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.4.3. Packet Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.4.4. Primary-clock procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4.5. Clock-update procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.4.6. Initialization Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.4.7. Clear Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4.8. Poll-update procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.5. Access Control Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 4. Filtering and Selection Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 4.1. Clock-filter procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 4.2. Clock-selection procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 5. Local Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 5.1. Standard Oscillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 5.2. Mathematical Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.3. Fuzzball Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 5.4. Uniform Phase Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 5.5. Nonuniform Phase Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 5.6. Maintaining Date and Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 8. Appendix A. NTP Data Format - Version 2 . . . . . . . . . . . . . . . . . . . . . . 45