[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:
>> 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!!

More information about the questions mailing list