Prior to the widespread use of networked computers, accurate timekeeping on personal computers was
relatively unimportant. With the advent of the Internet came the need for time synchronization
to support reliable timestamping and security protocols for government and military applications.
Network Time Protocol (NTP)
A protocol was
created that allowed remotely separated computers to transfer time amongst themselves using a
network. This time synchronization protocol is called the Network
Time Protocol (NTP) and
was pioneered by Dr. David Mills at the University of Delaware. NTP is very robust in its
determination of accurate time, however it ultimately depends upon the availability of a reliable
UTC time source.
UTC Time Sources
In the early days of the Internet, there were few available options for good UTC time references.
The most acceptable means of time dissemination in the United States during this era were the WWV
transmissions from Ft. Collins, Colorado. Unfortunately, propagation characteristics for this
system were not ideal and a few milliseconds of accuracy from the WWV receiver was all that could be
expected, with reception being sporadic.
The advent of the GOES timing receivers in the early 1980's improved the situation to the
100-microsecond level, but these units were expensive, coverage was not global, and their window of
applicability was short.
When GPS-derived time references arrived in the middle 1980's they were exotically expensive.
Though they delivered unprecedented reliability, accuracy and timing precision, few network administrators
could justify their expense solely for network time synchronization. There were no
out-of-the-box network time synchronization sources in those days,
so handmade solutions were the norm.
Before NTP Servers
Techniques were developed to timetag a 1 Pulse Per Second (1PPS) event applied to a signal on an
RS-232 port of a Unix server. The Unix server could be synchronized to better than
100 microseconds using this technique and then synchronize network workstations using NTP.
Drivers have been written and are freely available for almost every precision timing reference
receiver, GPS or otherwise, that has been manufactured in the last thirty years.
Plans for "gadget boxes", which provide the necessary interface hardware for converting
the 1PPS signal to the required RS-232 levels are also freely available.
Time Server Appliances
Eventually, in the early 1990's, manufacturers recognized the commercial potential for a timing
reference with an Ethernet connection that speaks NTP. These products are called Network Time
Servers, or NTP Servers, and they provide a convenient, reliable and relatively inexpensive way to
synchronize the time of all devices on a network.
Time Synchronization Accuracy
The timing accuracy of a GPS receiver in a Network Time Server is typically
100 nanoseconds. The accuracy of the NTP timestamp is within 10 microseconds of UTC, and network
factors, such as traffic and routers, reduce the overall network synchronization accuracy
to be typically within 1/2 to 2 milliseconds.
The engineers at EndRun Technologies have been designing Time Servers
using NTP since the mid-1990s. We specialize in the manufacture of very high-quality products.