Internet Time Synchronization : The Network Time Protocol

By Mills, D. L.

Book Id: WPLBN0000693695
Format Type: PDF eBook:
File Size: 0.1 MB
Reproduction Date: 2005

Title:	Internet Time Synchronization : The Network Time Protocol
Author:	Mills, D. L.
Volume:
Language:	English
Subject:	Arts, Humanities, Classical education
Collections:	Technical eBooks and Manuals Collection, Technical eBooks Collection
Historic Publication Date:
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Citation APA MLA Chicago L. Mill, B. D. (n.d.). Internet Time Synchronization : The Network Time Protocol. Retrieved from http://www.gutenberg.cc/

Description
Technical Reference Publication

Excerpt
Abstract: This memo describes the Network Time Protocol (NTP) designed to distribute time information in a large, diverse internet system operating at speeds from mundane to lightwave. It uses a returnabletime architecture in which a distributed subnet of time servers operating in a self-organizing, hierarchical, master-slave configuration synchronizes local clocks within the subnet and to national time standards via wire or radio. The servers can also redistribute time information within a network via local routing algorithms and time daemons.

Table of Contents
Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1. Performance Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2. Discussion of Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Time Standards and Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Network Time Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Implementation Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1.1. Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1.2. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1.3. State Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.3. Robustness Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4. Sample Processing and Selection Operations . . . . . . . . . . . . . . . . . . . . . 13 4.1. Data Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.2. Peer Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5. Local Clock Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6. NTP in the Internet System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 6.1. Time Servers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 6.2. Synchronization Subnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 6.3. Performance Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7. Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 List of Figures Figure 1. Implementation Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 2. NTP Packet Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 3. Calculating Delay and Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 4. Offset vs Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Figure 5. Phase-Lock Loop Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 6. Raw Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 7. Filtered Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 8. Error Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 List of Tables Table 1. Outlyer Selection Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17