
Building a Raspberry-Pi Stratum-1 NTP Server - dmmalam
http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html
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walrus01
Acquiring a signal by GPS does not make you stratum-1.

Stratum 1 servers are directly adjacent (within microseconds latency of, NOT
milliseconds) to stratum-0 servers, physically connected to atomic clocks.

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welterde
A good (timing) GPS receiver can easily get you within the sub-microsecond
region of UTC. And yes.. stratum 0 sources do include GPS as timing source.

Conversely having an atomic clock as frequency source, doesn't automatically
make you Stratum 0. You also have to synchronize it to the rest of the world
and the simplest method of doing so is GPS (unless you happen to be an
national laboratory).

For a Stratum 1 NTP server the local frequency source only has to provide
short term stability and perhaps for GPS reception outages (holdover
capability). And if you can live with a certain drift while the GPS is
unavailable then crystal oscillators are more than good enough for this
purpose.

