[ntp:questions] Re: Philosophical question about strata

Richard B. Gilbert rgilbert88 at comcast.net
Fri Oct 14 21:29:18 UTC 2005

David L. Mills wrote:

> Richard,
> 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 
> candidate.
> Dave
> Richard B. Gilbert wrote:
>> <snip>
>> 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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