[ntp:questions] NTP and SNTP in the end, give me precision of 1ms?

Unruh unruh-spam at physics.ubc.ca
Sun Sep 14 16:29:56 UTC 2008

David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:

>Hal Murray wrote:
>>> There is nothing per se that makes this system impossible to deliver 1ms. 
>>> Of course it depends of where those clients are-- if they are at the bottom
>>> of the sea communicating with 1bd/sec ultralow frequency radio, you will
>>> not get 1ms precision.
>> What's wrong with a (very) slow link?  As long as there aren't any
>> queueing delays, the delay should be symmetric in both directions
>> and I'd expect ntpd to work OK.

>A one baud link would have an uncertainty of a second in the time, 
>unless the transmit time stamps were synchronised with the signalling 
>units.  It would also have a delay that was on the limits of causing 
>rejection for a normal NTP implementation.

>A 1 bit/second link would definitely have an unacceptable delay.

>A 1 baud/second link would have a continually varying latency, and, 
>unless the bits per signalling unit varied to compensate, a continually 
>varying delay.  I don't think baud/second was the intended unit.  I 
>suspect he was suggesting a 1 bit per signalling unit, 1 signalling unit 
>per second, case.

Nope, 1 bit per sec as an off the top of my head estimate of the rate for
an ultra longwavelength radio link with a submarine under the ocean.

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