[ntp:questions] what happens when sys.peer turns stratum 16?

Rob nomail at example.com
Tue Jun 1 16:49:12 UTC 2010


unruh <unruh at wormhole.physics.ubc.ca> wrote:
> On 2010-06-01, Rob <nomail at example.com> wrote:
>> unruh <unruh at wormhole.physics.ubc.ca> wrote:
>>>> If we assume there is a private subnet that has two GPS reference
>>>> clocks to synchronize the rest of the machines, what would be the
>>>> expected failure mode where one of the stratum 1 servers go crazy, and
>>>> having three GPS clocks actually makes a difference?
>>>
>>> The gps falls off the roof and is burried in shrub, but still uses its
>>> internal clock to deliver PPS pulses is an example.
>>
>> It requires a badly coded GPS driver to make the NTP clock sync to
>> the GPS device while there are no satellites in view.   Any reasonable
>> driver checks the status messages and uses the time info only when there
>> is lock to the satellites.
>
> The PPS has no status info, or any other kind of info, except a beep
> every second. 

But in a GPS receiver there is always a related serial stream that
provides the status info in NMEA or manufacturer-specific binary
messages.  It is outright stupid to use PPS pulses from a GPS receiver
without evaluating this status stream.




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