RFC 957 (rfc957) - Page 2 of 27

Experiments in network clock synchronization

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 roundtrip delays in
   the Internet are discussed in [2].  A comprehensive mathematical
   treatment of the subject can be found in [1], while an interesting
   discussion on mutual-synchonization techniques can be found in [10].

   There are several ways accurate timestamps can be generated.  One is
   to provide at every service point an accurate, machine-readable clock
   synchronized to a central reference, such as the National Bureau of
   Standards (NBS).  Such clocks are readily available in several models
   ranging in accuracies of a few hundred milliseconds to less than a


Mills