[ntp:questions] Re: Philosophical question about strata
David L. Mills
mills at udel.edu
Sat Oct 15 15:47:47 UTC 2005
I didn't mean to finger you in particular, just trying to quell the
massive misinformation that seems to be flying these wires. We are
having a violent agreement.
Richard B. Gilbert wrote:
> David L. Mills wrote:
>> Really and truly do believe interpreting stratum as quality of service
>> is a bright red herring. It was never intended for that purpose. Its
>> primary purpose is avoiding timing loops. There is an absolutely
>> wonderful metric with which to interpret quality, a combination of
>> maximum error (synchronization distance) and estimated error (system
>> jitter). There are explicit provisions in the reference clock
>> interface that allow the driver to adjust these values with respect to
>> whatever statistics the clock provides. It would seem the PDoP
>> commonly provided by the GPS receiver firmware would be a prime
>> Richard B. Gilbert wrote:
>>> I don't think of stratum as an "estimate" of goodness. I think it's
>>> purely a designation of position in the hierarchy. A stratum one
>>> server is stratum one because it gets its time from a primary
>>> standard; e.g. an atomic clock. A server that gets its time from a
>>> WWV receiver is technically stratum one and can be several
>>> milliseconds off because of the vagaries of HF radio propagation.
>>> The "goodness" of a server also depends on the path through which you
>>> receive time from it. A client that is three thousand miles away
>>> from a stratum one server and receiving time over a heavily used
>>> network is probably getting time that is an order of magnitude
>>> poorer than a client three hundred feet away.
>>> Fudging a server to a higher stratum than it would normally have
>>> should make it appear less desirable to any client that has a choice
>>> of servers.
> I hope I didn't create the impression that I was arguing the opposite!!
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