Re: [ntp:questions] FW: Clock Offset
Mischanko, Edward T wrote: Thank you for your time in explaining this to me. Unfortunately, my * mathematics education stopped at intermediate algebra; it appears * that the formula is in calculus? Anyway, I feel like I have beaten The real point was to indicate that a formula isn't the most appropriate way of describing the filter used. You have to treat it as an algorithm. * this horse to death. I can accept the fact that they are different * and yet notice their similarities. I'm not sure Unruh completely * understands my point? ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
[ntp:questions] FW: Clock Offset
-Original Message- From: Mischanko, Edward T Sent: Friday, December 21, 2012 9:14 PM Subject: RE: [ntp:questions] Clock Offset -Original Message- From: questions- bounces+edward.mischanko=arcelormittal@lists.ntp.org [mailto:questions- bounces+edward.mischanko=arcelormittal@lists.ntp.org] On Behalf Of Terje Mathisen Sent: Thursday, December 20, 2012 2:42 AM To: questions@lists.ntp.org Subject: Re: [ntp:questions] Clock Offset Mischanko, Edward T wrote: No local clock is in use!! I was really questioning how the averaging algorithm could come up with a negative offset when none of the individual offsets were negative? That's (sort of) easy! The local clock offset is the best estimate of the (exponentially afair) averaging algorithm from the individual iterations of the control loop, while the ntpq -p gives you the last measurement from each server/clock source. I.e. they measure different things. Terje -- - Terje.Mathisen at tmsw.no almost all programming can be viewed as an exercise in caching ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions [Mischanko, Edward T] Terje, I do not doubt you, but if they are measuring different things to represent the same thing, then there is a formula off somewhere? Ed ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] FW: Clock Offset
On 2012-12-22, Mischanko, Edward T edward.mischa...@arcelormittal.com wrote: -Original Message- From: Mischanko, Edward T Sent: Friday, December 21, 2012 9:14 PM Subject: RE: [ntp:questions] Clock Offset -Original Message- From: questions- bounces+edward.mischanko=arcelormittal@lists.ntp.org [mailto:questions- bounces+edward.mischanko=arcelormittal@lists.ntp.org] On Behalf Of Terje Mathisen Sent: Thursday, December 20, 2012 2:42 AM To: questions@lists.ntp.org Subject: Re: [ntp:questions] Clock Offset Mischanko, Edward T wrote: No local clock is in use!! I was really questioning how the averaging algorithm could come up with a negative offset when none of the individual offsets were negative? That's (sort of) easy! The local clock offset is the best estimate of the (exponentially afair) averaging algorithm from the individual iterations of the control loop, while the ntpq -p gives you the last measurement from each server/clock source. I.e. they measure different things. Terje -- - Terje.Mathisen at tmsw.no almost all programming can be viewed as an exercise in caching ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions [Mischanko, Edward T] Terje, I do not doubt you, but if they are measuring different things to represent the same thing, then there is a formula off somewhere? No, they do not represent the same thing. They are different things. One is the instantaneously measured offset between the local clock and the servers. The other is the best estimate ntpd has for the difference between the local clock and true UTC time. Ed ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] FW: Clock Offset
unruh wrote: On 2012-12-22, Mischanko, Edward T edward.mischa...@arcelormittal.com wrote: I do not doubt you, but if they are measuring different things to represent the same thing, then there is a formula off somewhere? No, they do not represent the same thing. They are different things. One is the instantaneously measured offset between the local clock and the servers. The other is the best estimate ntpd has for the difference between the local clock and true UTC time. I don't believe he is now comparing the overall estimate with the most recent individual measurements. I think he is comparing the best estimate for an individual source, with the ntpq peers, most recent offset for that source. The formula for an individual filtered offset is something like: (z ^ n) * Offset where z is the Z-Transform operator and n is an natural number = 7, such that (z ^ n) * estimated-offset-error is minimal. Of course, it is not described that way in the actual code, and I don't think it is described that way in the documentation. I believe the error estimate includes the round trip delay, and the stratum, but it is that sort of thing that is subject to change. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] FW: Clock Offset
-Original Message- From: questions- bounces+edward.mischanko=arcelormittal@lists.ntp.org [mailto:questions- bounces+edward.mischanko=arcelormittal@lists.ntp.org] On Behalf Of David Woolley Sent: Saturday, December 22, 2012 6:14 PM To: questions@lists.ntp.org Subject: Re: [ntp:questions] FW: Clock Offset unruh wrote: On 2012-12-22, Mischanko, Edward T edward.mischa...@arcelormittal.com wrote: I do not doubt you, but if they are measuring different things to represent the same thing, then there is a formula off somewhere? No, they do not represent the same thing. They are different things. One is the instantaneously measured offset between the local clock and the servers. The other is the best estimate ntpd has for the difference between the local clock and true UTC time. I don't believe he is now comparing the overall estimate with the most recent individual measurements. I think he is comparing the best estimate for an individual source, with the ntpq peers, most recent offset for that source. The formula for an individual filtered offset is something like: (z ^ n) * Offset where z is the Z-Transform operator and n is an natural number = 7, such that (z ^ n) * estimated-offset-error is minimal. Of course, it is not described that way in the actual code, and I don't think it is described that way in the documentation. I believe the error estimate includes the round trip delay, and the stratum, but it is that sort of thing that is subject to change. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions [Mischanko, Edward T] David, Thank you for your time in explaining this to me. Unfortunately, my mathematics education stopped at intermediate algebra; it appears that the formula is in calculus? Anyway, I feel like I have beaten this horse to death. I can accept the fact that they are different and yet notice their similarities. I'm not sure Unruh completely understands my point? Regards, Ed ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
