RFC 958 (rfc958) - Page 1 of 14

Network Time Protocol (NTP)

Network Working Group                                         D.L. Mills
Request for Comments: 958                               M/A-COM Linkabit
                                                          September 1985

                      Network Time Protocol (NTP)


Status of this Memo

   This RFC suggests a proposed protocol for the ARPA-Internet
   community, and requests discussion and suggestions for improvements.
   Distribution of this memo is unlimited.

Table of Contents

   1.      Introduction
   2.      Service Model
   3.      Protocol Overview
   4.      State Variables and Formats
   5.      Protocol Operation
   5.1.    Protocol Modes
   5.2.    Message Processing
   5.3.    Network Considerations
   5.4.    Leap Seconds
   6.      References
   Appendix A. UDP Header Format
   Appendix B. NTP Data Format

1.  Introduction

   This document describes the Network Time Protocol (NTP), a protocol
   for synchronizing a set of network clocks using a set of distributed
   clients and servers.  NTP is built on the User Datagram Protocol
   (UDP) [13], which provides a connectionless transport mechanism.  It
   is evolved from the Time Protocol [7] and the ICMP Timestamp message
   [6] and is a suitable replacement for both.

   NTP provides the protocol mechanisms to synchronize time in principle
   to precisions in the order of nanoseconds while preserving a
   non-ambiguous date, at least for this century.  The protocol includes
   provisions to specify the precision and estimated error of the local
   clock and the characteristics of the reference clock to which it may
   be synchronized.  However, the protocol itself specifies only the
   data representation and message formats and does not specify the
   synchronizing algorithms or filtering mechanisms.

   Other mechanisms have been specified in the Internet protocol suite
   to record and transmit the time at which an event takes place,
   including the Daytime protocol [8] and IP Timestamp option [9].  The
   NTP is not meant to displace either of these mechanisms.  Additional
   information on network time synchronization can be found in the


Mills