[ih] The Importance of Time in the Internet

[Louis Mamakos]

On 4 Oct 2022, at 19:47, Toerless Eckert via Internet-history wrote:

> Time (synchronization) is just a marketing term for clock 
> (synchronization).

A good part of what an NTP implementation does computing the frequency 
and
phase errors.  Most people think of synchronizing clocks as making the 
phase
error as close to zero (e.g., close to the same "time".)   NTP also 
tries
to drive the frequency error close to zero (rate at which time advances) 
so
if you lose connectivity to the reference clock, at least your local 
clock
will continue to advance at the same rate.

When we did the first UNIX NTP implementation from the NTP spec at the
University of Maryland, it was fun to watch the computed frequency error
and relate it to the temperature of the room the (at the time NeXT)
workstation was in.  Looking at that change hour to hour and day by day
revealed that the HVAC in the campus office building was a bit more
"relaxed" over the weekends.

One fun anecdote I recall from that time was using NTP to discover that
NOAA had repositioned a satellite.  At the time, there was a GOES 
satellite
clock that was used as an NTP reference.  It decoded a signal from one 
of
the NOAA weather satellites in geosynchronous orbit.  When you installed 
the
clock, you had to configure what the path delay was to the spacecraft in
orbit, based on your position on the ground.   At some point, it was 
noticed
that the GOES clock offset error had increased relative to others, and 
later
found out that NOAA had repositioned the spacecraft in orbit to cover 
for a
failed satellite covering the western part of the US.  This of course 
changed
the path delay.

Other fun was watching the clock offset on a fuzzball using a 60HZ 
power-line
based clock (rather than some local quartz crystal oscillator.)  You 
could
watch the error and see the AC line frequency sag as the load increased, 
and
then later at night, speed up to take up the slack.  So that all those 
wall
clocks with AC line-driven synchronous motors wouldn't "lose time" - 
just the
right number of 60Hz AC line cycles per day.

It was all great fun, especially explaining to my wife how, on New 
Year's Eve
we couldn't rush off to some party because I needed to be at home at 
(UTC)
midnight to see of the leap-second code was going to do the right thing.

Louis Mamakos