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Experiments in network clock synchronization (RFC0957)

IP.com Disclosure Number: IPCOM000004953D
Original Publication Date: 1985-Sep-01
Included in the Prior Art Database: 2001-Jul-12
Document File: 28 page(s) / 69K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

D.L. Mills: AUTHOR

Abstract

2. Design of the Synchronization Algorithm 2.1. The Logical Clock 2.2. Linear Phase Adjustments 2.3. Nonlinear Phase Adjustments 3. Synchronizing Network Clocks 3.1. Reference Clocks and Reference Hosts 3.2. Distribution of Timing Information 4. Experimental Validation of the Design 4.1. Experiment Design 4.2. Experiment Execution 4.3. Discussion of Results 4.3.1. On Power-Grid Clocks 4.3.2. On Clocks Synchronized via Network Links 4.3.3. On the Accuracy of Radio Clocks 4.3.3.1. The Spectracom 8170 WWVB Radio Clock 4.3.3.2. The True Time 468-DC GOES Radio Clock 4.3.3.3. The Heath GC-1000 WWV Radio Clock 4.3.4. On Handling Disruptions 4.4. Additional Experiments 5. Summary and Conclusions 6. References

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Network Working Group D.L. Mills Request for Comments: 957 M/A-COM Linkabit

September 1985

Experiments in Network Clock Synchronization

Status of this Memo

This RFC discusses some experiments in clock synchronization in the ARPA-Internet community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited.

Table of Contents

1. Introduction 2. Design of the Synchronization Algorithm 2.1. The Logical Clock 2.2. Linear Phase Adjustments 2.3. Nonlinear Phase Adjustments 3. Synchronizing Network Clocks 3.1. Reference Clocks and Reference Hosts 3.2. Distribution of Timing Information 4. Experimental Validation of the Design 4.1. Experiment Design 4.2. Experiment Execution 4.3. Discussion of Results 4.3.1. On Power-Grid Clocks 4.3.2. On Clocks Synchronized via Network Links 4.3.3. On the Accuracy of Radio Clocks 4.3.3.1. The Spectracom 8170 WWVB Radio Clock 4.3.3.2. The True Time 468-DC GOES Radio Clock 4.3.3.3. The Heath GC-1000 WWV Radio Clock 4.3.4. On Handling Disruptions 4.4. Additional Experiments 5. Summary and Conclusions 6. References

List of Figures

Figure 1. Clock Registers Figure 2. Network Configuration

Mills [Page 1]

RFC 957 September 1985 Experiments in Network Clock Synchronization

List of Tables

Table 1. Experiment Hosts Table 2. Link Measurements Table 3. First Derivative of Delay Table 4. GOES Radio Clock Offsets Table 5. WWV Radio Clock Offsets Table 6. ISI-MCON-GW Clock Statistics Table 7. LL-GW Clock Statistics Table 8. LL-GW Clock Statistics

1. Introduction

One of the services frequently neglected in computer network design is a high-quality, time-of-day clock capable of generating accurate timestamps with small residual errors compared to intrinsic one-way network delays. Such a service would be useful for tracing the progress of complex transactions, synchronizing cached data bases, monitoring network performance and isolating problems.

Several mechanisms have been specified in the Internet protocol suite to record and transmit the time at which an event takes place, including the ICMP Timestamp message [6], Time Protocol [7], Daytime protocol [8] and IP Timestamp option [9]. A new Network Time Protocol [12] has been proposed as well. Additional information on network time synchronization can be found in the References at the end of this document. Synchronization protocols are described in [3] and [12] and synchronization algorithms in [2], [5], [10] and [11]. Experimental results on measured roundtrip delays in the Internet are discussed in [4]. A comprehensive mathematical treatment of clock synchronization can be found in [1].

Several mechanisms have been specified in the Internet protocol suite to record and transmit the time at which an event takes place, including the ICMP Timestamp message [6], Time protocol [7], Daytime protocol [8] and IP Timestamp option [9]. Issues on time synchronization are discussed in [4] and synchronization algorithms in [2] and [5]. Experimental results on measured roundtr...