[ntp:questions] NTP and SNTP in the end, give me precision of 1ms?
uwe_klein_habertwedt at t-online.de
Sun Sep 14 13:29:06 UTC 2008
David Woolley wrote:
> Uwe Klein wrote:
>> DCF77 for example is a "1 bit/s" transmission, a sentence taking 60s.
>> It seems to not have issues with ms syncing.
> That's because it transmits rather a large number of bits per signalling
> unit. log2(resolution of timing of edge within second) bits of time
> information are sent on any long or short signalling unit. (In
> practice, you won't recover every bit on every measurement, so you need
> several seconds to improve the signal to noise ratio. Once one is
> synchronised, the number of useful bits drops greatly, because there is
> a very high level of redundancy in the coding.)
> There is nothing in NTP protoco that guarantees that signalling units
> are second aligned. However, one could get high resolution on very slow
> links by making the transmit time represent the start of signalling unit
> time, rather than the time the transmit request was queued. That would
> require special, low level, drivers.
sure, you need a syncronised "carrier" or exact timestamps.
But isn't that the basic assumption in all existing systems
i.e edge or phase of the bitstream carries relevant information?
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