Re: [LEAPSECS] UT1 offset

[Seaman, Robert Lewis - (rseaman)]

Hi Tom and Mike and all,

I suppose we weren’t talking about DUT1 time signals?

See http://futureofutc.org/2011/program/presentations/AAS_11-675_Malys.pptx.pdf 
for details about the flipside question of operating a GNSS constellation 
(current as of a dozen years ago).

One shouldn’t find it surprising (at least, I don’t find it surprising) if 
navigating and calibrating constellations of Earth-orbiting satellites requires 
knowledge of Earth orientation. At some point during the 2011 Exton workshop, 
there was a discussion of GPS being able to detect motions due to plate 
tectonics. Earth orientation doesn’t necessarily need to be provided in terms 
of UT1, and the temporal geophysicists presumably need higher-order moments as 
well. One doubts the majority of satellites need such precision.

Rob

On 1/2/24, 7:45 AM, "LEAPSECS" wrote:


External Email

Hi Mike,

> the system needs an estimate of current UT1

Can you give some references to your observation? I don't recall seeing UT1 
mentioned in the first couple of decades of GPS documentation. The system runs 
on GPS time, the WGS84 coordinate system, broadcast ephemeris including SV 
clock corrections. Where does UT1 appear in those?

> That estimate is applied internally so the end user does not need to know the 
> details

Right, the user is shielded from many details. But I didn't think even GPS 
receivers had knowledge of UT1, nor the satellites themselves. So where in "the 
system" does UT1 apply?

Thanks,
/tvb

On 12/28/2023 1:23 AM, Mike Hapgood - STFC UKRI via LEAPSECS wrote:
Jim outlines a calculation I've done many times. But there's a similar 
calculation for GNSS systems (GPS, Galileo, Beidou, etc). If you want to use 
GNSS to determine positions on Earth's surface to accuracy of a few metres, the 
system needs an estimate of current UT1 accurate at least to a few 
milliseconds. That estimate is applied internally so the end user does not need 
to know the details, just as that user does not need to know about the 
relativistic clock corrections or corrections for ionospheric signal delay that 
also underpin safe use of GPS. But the bottom line is that knowledge of UT1 
(i.e. the spin phase of the Earth) is essential for GNSS - and many other space 
systems.

Mike

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[LEAPSECS] timekeeping resources for 2024?

[Seaman, Robert Lewis - (rseaman)]

Happy Holidays,

I started to reply to recent emails, but all issues except one have been 
discussed over and over again on the mailing list and at the various workshops. 
So, my Christmas gift to you all is not to reply, and to myself was to dust off 
the login and server info for the futureofutc.org site (it has passed through a 
succession of web hosting companies and tech suites). I have updated the links 
for the presentations, discussions, and preprints for the 2011 and 2013 
workshops to point away from the original lost host at Caltech. The 2014 
session at the American Astronomical Society meeting is thrown in for good 
measure:

http://futureofutc.org
http://futureofutc.org/2011
http://futureofutc.org/aas223

Please advise of any remaining broken links (some of the 3rd party links have 
gone stale, for instance) and suggest additional online resources to add to a 
new 2024 links tab. Folks with institutional access might want to also download 
the proceedings from “The Science of Time 2016”:

https://ui.adsabs.harvard.edu/abs/2017ASSP...50.A/abstract

For example, see chapter 28: “How Gravity and Continuity in UT1 Moved the 
Greenwich Meridian”, by Malys, Seago, Pavlis, Seidelmann, and Kaplan.

The one issue that has not been sufficiently addressed is the standards, 
protocols, funding, and logistics for future infrastructure supporting mean 
solar time now that UTC won’t. (UT1 is an observational time scale that is only 
known a couple of months after the fact.) Perhaps significant work has been 
done recently on these infrastructure issues. Pointers would be welcome.

Other custodians of civil time resources are encouraged to review and enhance 
them in 2024.

Best wishes to all in the New (leap) Year!

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona
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Re: [LEAPSECS] prep for WRC 23

[Seaman, Robert Lewis - (rseaman)]

E pur si muove

UTC may no longer serve as a kind of solar time (after 2026 or 2035, or 
somebody said 2040 the other day), but civil time will continue to have 
engineering requirements tracing to both solar and atomic time scales. 
Shenanigans will result, bedeviling future blinkered technocrats.

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona


On 12/22/23, 12:42 PM, "LEAPSECS" wrote:

Resolution 655 was approved by the WRC plenary, reportedly in a
very routine manner and with with neither drama nor long speeches.

The full text of the resolution is on page 399 of the provisional final acts:

https://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-WRC.15-2023-PDF-E.pdf

My Tl;dr version of the resolution is:

Timescales are not spectrum regulation, we defer to CPGM
and BIPM on that, but will handle any fall-out as far as
radio signals go.  Please keep DUT1 less than 100 seconds.

Then BIPM then issued this press release:

https://www.bipm.org/en/-/2023-12-12-wrc-dubai

Which I read as death notice for the leap-second, with further
details of the funeral to announced after CPGM's meeting in 2026.

--
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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[LEAPSECS] "Why the day is 24 hours long"

[Seaman, Robert Lewis - (rseaman)]

The Babylonians would perhaps aver this is not the best possible title: “Why 
the day is 24 hours long: The history of Earth’s atmospheric thermal tide, 
composition, and mean temperature”. In any event, there are lots of resonances 
and near-resonances in the solar system. If any dynamicists are reading, please 
comment on the geophysics.

https://arstechnica.com/science/2023/07/the-gravitational-interactions-that-have-helped-us-dodge-60-hour-days/

Not sure why “dodge” would be the right verb here. As one comment says: 
“Apparently every planet gets a predetermined set of hours before it explodes. 
Like a hot pocket in a microwave.” Fewer, longer days might have been 
preferable.

It’s so rare that we get a new talking point here. This morning’s breakfast 
burrito attests to the microwave-derived insight.

Rob

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Re: [LEAPSECS] speeding up again?

[Seaman, Robert Lewis - (rseaman)]

This point of view (from Richard’s second citation) is rather backward: “LOD is 
the negative time-derivative of UT1-UTC”, whatever its mathematical utility. 
And whatever one’s philosophical position on the topic of this list.

I’m a little at a loss for what we’re discussing here. The astronomically 
long-term trend is that Earth’s angular momentum is being transferred to the 
Moon. This is a list for picking nits, so by all means, proffer issues of the 
Earth-Moon barycenter or orbital or spin dynamical effects in the solar system. 
But in any event, the overall trend is not for a shortening or flat length of 
day but for LOD to lengthen. And for lab-coated acolytes of atomic time to 
clutch their pearls over its integral playing bloody hell with UTC.

Why, then, are we seeking additional explanations for effects that act to 
restore this overall trend? We were surprised at (and some of us were rooting 
for) the possibility of a negative leap second. Now this seems less likely. 
Isn’t that the expected (if disappointing for some) result?

A similar answer would apply to the overheated rhetoric in the media about the 
Earth’s core “spinning backward”, rather than more accurate but more boring 
phrases like “slightly greater excursions from the overall trend than have been 
seen in a few decades”. This is to say that there are a lot more immediate 
negative effects of AGW than hypothesizing that it is enhancing ENSO (or 
whatever the argument is here) and will cause Armageddon via a negative leap 
second.

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona



On 6/17/23, 5:59 AM, "LEAPSECS" wrote:

External Email

https://www.science.org/content/article/longer-days-brought-you-el-ni-o

Also:
Investigating the Relationship Between Length of Day and El-Niño Using Wavelet 
Coherence Method:
https://link.springer.com/chapter/10.1007/1345_2022_167

-- Richard Langley

-
| Richard B. LangleyE-mail: l...@unb.ca |
| Geodetic Research Laboratory  Web: http://gge.unb.ca  |
| Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142   |
| University of New Brunswick   |
| Fredericton, N.B., Canada  E3B 5A3|
|Fredericton?  Where's that?  See: http://www.fredericton.ca/   |
-


From: LEAPSECS  on behalf of Tom Van Baak 

Sent: June 15, 2023 10:48 PM
To: leapsecs@leapsecond.com
Subject: Re: [LEAPSECS] speeding up again?

✉External message: Use caution.

Steve,

> We can probably put a lot of the blame onto El Niño

That sounds plausible but I'm suspicious of quick and simple explanations.

You work at/for a university, near the coast, yes? Can you ping some of your 
climatology / oceanography colleagues and get data going back as far as they 
have it? I think it would be useful to see what the correlation coefficient 
actually is.

Attached is an LOD plot I made a while ago. A random web google link says "The 
five strongest El Niño events since 1950 were in the winters of 1957-58, 
1965-66, 1972-73, 1982-83 and 1997-98". To my eyeball I just don't see that in 
the historical LOD plot.

/tvb

On 5/26/2023 9:09 AM, Steve Allen wrote:

On Mon 2023-05-22T16:44:30+0200 Tony Finch hath writ:


The prospect of a negative leap second is receding. The longer-term
projected length of day from Bulletin A has been increasing towards 24h
in recent months.



We can probably put a lot of the blame onto El Niño

--
Steve Allen  
WGS-84 (GPS)
UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
1156 High Street   Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064   https://www.ucolick.org/~sla/  Hgt +250 m


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Re: [LEAPSECS] USNO predictions of UT1-UTC

[Seaman, Robert Lewis - (rseaman)]

Isn’t the question whether those responsible for issuing leap seconds will 
follow through and trigger a negative leap second even if Bulletin A says it’s 
time? Much consternation will be feigned.

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona


On 3/19/23, 5:21 PM, "LEAPSECS" wrote:

On Sun 2023-03-19T19:24:56-0400 Demetrios Matsakis via LEAPSECS hath writ:
> https://insidegnss.com/will-we-have-a-negative-leap-second/
> Will We Have a Negative Leap Second?

The USNO predictions in IERS Bulletin A have been pretty good...

https://www.ucolick.org/~sla/leapsecs/bulla52w.html

It will be interesting to see what kind of consternation arises
if the predictions start saying the negative leap is impending.

Somewhere in USNO/UKHO somebody has been making longer term
predictions for use in the navigational almanacs, but as far
as I know those have never been published.

--
Steve Allen  WGS-84 (GPS)
UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
1156 High Street   Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064   https://www.ucolick.org/~sla/  Hgt +250 m
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Re: [LEAPSECS] future access to solar time?

[Seaman, Robert Lewis - (rseaman)]

Interesting!

Another example of “polysemy” 
(http://hanksville.org/futureofutc/aas223/presentations/2-1-ISOterminologyAAS.pdf)
 in timekeeping.

In addition to changes in funding (be careful what you ask for, precision time 
community), best practices (and worse practices) should get a good workout as 
this foundational standard is redefined.

Rob



On 11/21/22, 8:30 AM, "LEAPSECS" wrote:

On 2022-11-21 14:19, Seaman, Robert Lewis - (rseaman) wrote:

> In a post-leap-second world, precision values for dUT1 either become more 
> critical or less. Or rather, they become no-less important scientifically but 
> perhaps negligible politically. For 
> example,https://www.sciencedirect.com/science/article/pii/S0273117719302388  
> says “Global Navigation Satellite Systems (GNSS) are dependent on VLBI as 
> they need dUT1 to maintain its operability”.



I am not sure if we mean the same thing by "dUT1". I used
it in the sense:
   dUT1 is an additonal correction to UTC so that
   UTC +  DUT1 + dUT1
   is a better approximation of UT1 than just
   UTC +  DUT1
   and takes its values in the set {0, ±20, ±40, ±60, ±80} ms.

dUT1 in this sense is used only by some Russian time signals,
and its value is not defined by the IERS. Moreover, since the
amplitude of UT1 - UT2 is about 34 ms, dUT1 must be adjusted
for annual variations of UT1 - UTC.

I have seen the term "dUT1" to be used for ΔUT1 = UT1 - UTC
(and that is how I read it in the paper you quoted), and
also for the rate d(UT1) -- but these are different beasts.

Michael Deckers.

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Re: [LEAPSECS] future access to solar time?

[Seaman, Robert Lewis - (rseaman)]

Interesting. In a post-leap-second world, precision values for dUT1 either 
become more critical or less. Or rather, they become no-less important 
scientifically but perhaps negligible politically. For example, 
https://www.sciencedirect.com/science/article/pii/S0273117719302388 says 
“Global Navigation Satellite Systems (GNSS) are dependent on VLBI as they need 
dUT1 to maintain its operability”. To the UTC decision-makers does 
“operability” mean legal constraints or does it mean physical reality / 
technical infrastructure? (“UTC no longer depends on UT1, so why should we pay 
for it?”)

For UTC/GPS context, Stephen Malys had a talk at the Exton meeting in 2011: 
http://hanksville.org/futureofutc/2011/preprints/32_AAS_11-675_Malys.pdf, but I 
don’t see the question of high precision requirements addressed directly (and 
much may have changed in 11 years).

Which is to ask, I suppose, will redefining UTC imply that activities like VLBI 
will need to seek different funding streams?

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona



On 11/21/22, 6:37 AM, "LEAPSECS" wrote:

On 2022-11-20 15:15, Tony Finch asked:
>   (Do any of
> the national broadcast signals actually follow the ITU spec?)


Lists of UTC time signals with details about the coding are in
the Annual reports of the BIPM time department, at
[https://www.bipm.org/en/time-ftp/annual-reports].
A few of them transmit DUT1 (and even dUT1).

Michael Deckers.

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Re: [LEAPSECS] future access to solar time?

[Seaman, Robert Lewis - (rseaman)]

Hi Tony,

The time zone system and daylight-saving time are layered on UTC. My clock 
shows Mountain Standard Time year-round. Other people’s show other local times 
and 10-15% of these change by an hour twice a year. These small complications 
will not be made simpler by attempting to remove the concept of mean solar time 
from the system. Those who want to dispute this might ask themselves why they 
bother, considering the lab-coated acolytes of atomic time have already voted 
to redefine UTC.

Similarly, complications like the equation of time and its graphical 
representation as the analemma don’t change the (current) fundamental 
traceability back to mean solar time. See innumerable discussions on this list 
or at meetings like Exton or Charlottesville. We are ultimately not talking 
about the “leap second” we are talking about the definition of the word “day”.

Many astronomical systems do care at the level of the current UTC 
approximation. Some care at much higher precision. So, what alternative 
standards and infrastructure will be available in the future?

Time to move on…

Rob


On 11/20/22, 10:31 AM, "LEAPSECS" wrote:

External Email

Seaman, Robert Lewis - (rseaman)  wrote:
>
> Getting the solar time currently means looking at your watch or the
> upper right-hand corner of the monitor.

Well, no, not for more than half the year. I happen to be close to the
Greenwich meridian so my clocks currently show something close to mean
solar time (about 30 seconds fast, I think?) but that isn't true for most
people.

I assumed from your complaint about losing access to solar time that you
cared about roughly-second or subsecond precision, because if your
precision requirements are "look at the clock on the wall" your complaint
does not make sense. The clock on the wall tells the time for social
purposes, not for the position of the sun in the sky.

--
Tony Finchhttps://dotat.at/
Isle of Man: West 5 or 6, backing south 3 or 4, then southeast 6 or 7
later. Mainly moderate, becoming slight for a time. Showers, rain
later. Mainly good, becoming moderate or poor later.
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Re: [LEAPSECS] future access to solar time?

[Seaman, Robert Lewis - (rseaman)]

Hi Tony,

Getting the solar time currently means looking at your watch or the upper 
right-hand corner of the monitor. Would anybody else’s summary of the notion of 
“easy access” include phrases like: “8.23 bits two’s complement fixed point” or 
“NMEA sentences that contain anything like UT1 or DUT1 or delta-T”?

I have been presuming tenth-second DUT1 values are slated for demolition with 
leap seconds. Can anybody confirm differently? I applaud the goal of ensuring 
understanding and usage of whatever infrastructure will exist. Few systems 
currently use DUT1. One of the issues is that many more will need to start.

UT1 itself is only known retroactively. If your use of the word “stunt” wasn’t 
a typo, it seems to me that NIST rather needs robust and easy-to-use 
infrastructure. I was never able to get reliable access to the UT1 NTP server, 
and generally, our group doesn’t build reliance on third-party NTP pools into 
our operational systems.

We should all welcome GNSS support for access to UT1 (or a coherent variation 
known in advance), but as you suggest this will require new infrastructure and 
standards. Perhaps I’m off the mark, but that most definitely doesn’t imply 
anybody else has yet found the mark themselves.

Rob


Seaman, Robert Lewis - (rseaman)  wrote:

> The plan, rather, is to cease easy access to solar time.

The resolution says the GCPM

: encourages the BIPM to work with relevant organizations to identify the
: need for updates in the different services that disseminate the value of
: the difference (UT1-UTC) and to ensure the correct understanding and use
: of the new maximum value.

So I think your summary is a bit off the mark.

I guess the ITU is going to revise TF.460 to allow larger values of DUT1
in time signals, and MSF etc. will accommodate the change too. (Do any of
the national broadcast signals actually follow the ITU spec?)

GPS L5 signals provide UT1 as an 8.23 bits two's complement fixed point
difference from GPS time. This is enough to cope with the changes in the
CGPM resolution. See IS-GPS-705 p. 87 at https://www.gps.gov/technical/icwg/

I have not been able to find any specs for NMEA sentences that contain
anything like UT1 or DUT1 or delta-T, but I expect they will be created
before too long, as more GPS receivers support L5 signals.

And there are other sources of UT1 like NIST's stunt NTP servers.

--
Tony Finchhttps://dotat.at/

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[LEAPSECS] future access to solar time?

[Seaman, Robert Lewis - (rseaman)]

Whatever they do to poor old UTC and by extension to the concept of Universal 
Time as the modern realization of Greenwich Mean Time, atomic time and solar 
time will continue to be separate kinds of time scales, both of which are 
necessary for diverse engineering requirements for civil timekeeping, as well 
as for technical applications.

“Ceasing leap seconds” is an incoherently stated goal since there already are 
timescales without leaps. The plan, rather, is to cease easy access to solar 
time.

The past 20 years have seen a concerted effort to avoid the 2003 Torino 
consensus to define a new leap-less time scale. We now have a few years before 
Universal Time becomes Universal-except-for-solar Time. Could we perhaps spend 
the time more productively and design a new solar time scale, with-or-without 
leaps? UT1 as it currently exists is not sufficient. Flat files on 19th-century 
servers are not sufficient.

Arnold Rots supplied an excellent diagram of timescales in the solar system for 
a session we held at the 2014 meeting of the American Astronomical Society:

http://hanksville.org/futureofutc/aas223/

None of this complexity goes away by waving a wand to vanish leap seconds. 
Rather, the green box between UTC and UT1 gets much more complicated, including 
some fictional future leap-minute or repeated redefinitions of worldwide time 
zones or some fantasy of the whole world moving to a single time zone.

What are the overall engineering requirements for the multi-timescale 
system-of-systems? What are the best practices for evaluating possible 
timekeeping infrastructure and standards in a world that freezes UTC at a 
static offset from TAI? The concept of operations isn’t limited to how our 
gill-equipped, web-fingered descendants will implement a leap-hour long after 
we’re all dead. Maybe they’ll switch to tide-based clocks.

The question is how do we optimize access to the diversity of time scales 
starting now?

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona
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Re: [LEAPSECS] Executive Order on Strengthening National Resilience through Responsible Use of Positioning, Navigation, and Timing Services

[Seaman, Robert Lewis - (rseaman)]

Conceivably Ruth Belville might satisfy the language: 
https://en.wikipedia.org/wiki/Ruth_Belville#/media/File:Ruth_Belville_1908.jpg
--


On 2/13/20, 7:37 AM, "LEAPSECS on behalf of Richard Langley" 
 wrote:

Yes, I don't think Mr. Trump came up with the language or even read it. ;-) 
Not sure where Canada stands on the subject at the moment (I'll enquire), but 
the U.S. effort might be driven by DoT through its Positioning, Navigation, and 
Timing (PNT) & Spectrum Management division under the Assistant Secretary for 
Research & Technology. Testing of alternative PNT systems is planned or already 
underway:
https://www.gpsworld.com/gps-backup-demonstration-projects-explained/
-- Richard


-
| Richard B. LangleyE-mail: l...@unb.ca 
|
| Geodetic Research Laboratory  Web: http://gge.unb.ca/ 
|
| Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142   
|
| University of New Brunswick   
|
| Fredericton, N.B., Canada  E3B 5A3
|
|Fredericton?  Where's that?  See: http://www.fredericton.ca/   
|

-



> On Feb 13, 2020, at 10:14 AM, Seaman, Robert Lewis - (rseaman) 
 wrote:
> 
> ⚠External message: Use caution.
> 
> Hi Richard,
> 
> Interesting! A few immediate comments / questions:
> 
> 1) Political talk to /dev/null
> 2) Whether as executive order or otherwise, language like this obviously 
originated with experts.
> 3) Does anybody know what agenc(ies) appears to be motivating this?
> 4) Are commercial interests involved?
> 5) Are similar actions being taken in Canada or other countries?
> 6) Is PNT singled out, or are there similar orders for other technologies 
and risk profiles?
> 7) I don't see "leap second" or terms like "NTP" mentioned here.
> 
> Six months is remarkably aggressive, even notionally, and there's no 
definition of what "source of UTC" means, or even "GNSS-independent". Is some 
specific technology or even vendor already implied?
> 
> Rob Seaman
> University of Arizona
> --
> 
> 
> On 2/13/20, 6:47 AM, "LEAPSECS on behalf of Richard Langley" 
 wrote:
> 
>"(i)  Within 180 days of the date of this order, the Secretary of 
Commerce shall make available a GNSS-independent source of Coordinated 
Universal Time, to support the needs of critical infrastructure owners and 
operators, for the public and private sectors to access."
> 
>
https://www.whitehouse.gov/presidential-actions/executive-order-strengthening-national-resilience-responsible-use-positioning-navigation-timing-services/
> 
>
-
>| Richard B. LangleyE-mail: l...@unb.ca
 |
>| Geodetic Research Laboratory  Web: 
http://gge.unb.ca/ |
>| Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 
453-5142   |
>| University of New Brunswick  
 |
>| Fredericton, N.B., Canada  E3B 5A3   
 |
>|Fredericton?  Where's that?  See: http://www.fredericton.ca/  
 |
>
-
> 
> 
> 
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Re: [LEAPSECS] Executive Order on Strengthening National Resilience through Responsible Use of Positioning, Navigation, and Timing Services

[Seaman, Robert Lewis - (rseaman)]

Hi Richard,

Interesting! A few immediate comments / questions:

1) Political talk to /dev/null
2) Whether as executive order or otherwise, language like this obviously 
originated with experts.
3) Does anybody know what agenc(ies) appears to be motivating this?
4) Are commercial interests involved?
5) Are similar actions being taken in Canada or other countries?
6) Is PNT singled out, or are there similar orders for other technologies and 
risk profiles?
7) I don't see "leap second" or terms like "NTP" mentioned here.

Six months is remarkably aggressive, even notionally, and there's no definition 
of what "source of UTC" means, or even "GNSS-independent". Is some specific 
technology or even vendor already implied?

Rob Seaman
University of Arizona
--


On 2/13/20, 6:47 AM, "LEAPSECS on behalf of Richard Langley" 
 wrote:

"(i)  Within 180 days of the date of this order, the Secretary of Commerce 
shall make available a GNSS-independent source of Coordinated Universal Time, 
to support the needs of critical infrastructure owners and operators, for the 
public and private sectors to access."


https://www.whitehouse.gov/presidential-actions/executive-order-strengthening-national-resilience-responsible-use-positioning-navigation-timing-services/


-
| Richard B. LangleyE-mail: l...@unb.ca 
|
| Geodetic Research Laboratory  Web: http://gge.unb.ca/ 
|
| Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142   
|
| University of New Brunswick   
|
| Fredericton, N.B., Canada  E3B 5A3
|
|Fredericton?  Where's that?  See: http://www.fredericton.ca/   
|

-



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Re: [LEAPSECS] Leap seconds have a larger context than POSIX

[Seaman, Robert Lewis - (rseaman)]

Hello all,

The fundamental answer / constraint to all questions of engineering, including 
temporal engineering, is funding. No bucks, no Buck Rogers. “Time” is a vast 
topic, pretty much as big as “space”. Precision timekeeping topics are only 
somewhat smaller in practical terms since issues of anthropology and 
philosophy, etc., that may be far afield in other kinds of engineering, remain 
remarkably pertinent.

Funding falls into per-project and per-community responsibilities. Per-project, 
the engineering requirements related to timekeeping are remarkably diverse. You 
can read about the resulting timekeeping solution we implemented in support of 
our Near-Earth Asteroid (NEA) survey (https://arxiv.org/abs/1807.01370), but 
the precise mix of ingredients varies even between astronomical observatories. 
The short answer, per-project, is that organizations should plan and budget for 
timekeeping just as with any other critical infrastructure.

For example, we operate facilities in 6 buildings in 3 diverse locations, 
including two remote mountaintops. So we bought 3 commercial GNSS clocks and 
ran fiber between the pairs of buildings. We are extremely happy with the 
quality and support we have received from Meinberg, and I am happy to leave the 
NTP server-side updates to them, rolled into their occasional firmware updates. 
These updates have included significant feature improvements, including a nifty 
time synchronization monitor tool. My boss might call it the world’s most 
boring video game, but really that’s kind of the point. Many of the figures in 
the preprint above came directly from our Meinberg clocks. The cost of these 
clocks and related equipment is in the ballpark (baseball for “similar to”) for 
other classes of computing infrastructure. We don’t expect commodity computers 
to do hardware time-capture out of the box.

At the moment we are commissioning operations on another telescope on yet 
another mountaintop and will probably buy another GNSS clock to provide both 
hardware time capture and NTP services. We are also planning a project-wide OS 
upgrade for which chronyd is the default NTP option and are evaluating its 
performance, which is to say that project timekeeping operations costs continue.

Per-community, NTP is just one tool in a larger toolkit, but even so the 
panoply of NTP engineering requirements across many hundreds or thousands of 
projects is more diverse than POSIX or IETF have ever even attempted to 
capture, and funding has to compete with many other host-level and 
network-level standards. The Network Time Foundation (https://www.nwtime.org) 
supports the core NTP project, but NTF’s responsibilities are themselves 
broader than NTP. How many organizations support (financially) all the 
organizations like NTF that are responsible for standards, APIs, and protocols 
they rely on? Heck, how many of us read and respond to this 
professionally-relevant mailing list off-the-clock (as it were), as I am doing 
right now, rather than during work hours?

Many people reading this are their organization’s expert on timekeeping issues, 
and time is likely of significant importance to your organization if you are 
still reading to the end of this message. Ask yourself if your project, 
company, or community budgets for timekeeping infrastructure, operations, and 
standards proportional to their impact and risks, positive and negative, to 
your mission? I believe one reason Meinberg added its very useful syncmon tool 
was to address customers’ precise-timekeeping reporting requirements, 
especially for financial institutions, who attach equally precise estimates of 
its value in units of currency.

What’s time worth to you?

Rob Seaman
Catalina Sky Survey
Lunar and Planetary Laboratory

(I have no financial interests in Meinberg or NTF.)
--

Hi Hal,

It's 2020. How on earth can NTP still not implement UTC correctly, in all 
cases? Or is it a fundamental NTP design flaw?

The Z3801A issue doesn't sound like an NTP problem. This is a known legacy 
Z3801A f/w or Motorola Oncore problem, yes? Maybe also affected by one or even 
two GPS WNRO problems buy now?

/tvb

On 2/6/2020 1:41 AM, Hal Murray wrote:

tvb said:

There's no ambiguity. Those are just bugs. No software should depend on  more

than 1 month notice of a leap second and no software should be  fooled if the

notice is months or even years in advance.

There are plenty of quirks in ntp code along that line.  The APIs don't have

an explicit when.  The NTP-Kernal API for leap-pending is leap-tonight.  You

have most of the next day to turn it off.  The leap-pending on the wire is

leap-at-the-end-of-this-month.



I fixed a bug in the Z3801 driver by ignoring a leap pending unless it was

June or December.  It's a hack, but it gets the job done and the code wasn't

setup to ask it when the leap would happen.





tvb said:

If you're writing a FAQ or best practices guide stay in touch. I have a

semi-technical leap 

[LEAPSECS] Leap seconds have a larger context than POSIX

[Seaman, Robert Lewis - (rseaman)]

Tried to send this a few days ago, but it never showed up on the list. Steve 
has provided gritty details since.

Since roughly the second world war, the distinction between time-of-day and 
interval-time has become increasingly clear. But the history of this 
distinction goes back at least as far as Galileo. UTC was an attempt to serve 
both Universal Time (time-of-day) and Atomic Time (interval timing) using a 
single standard.

Folks in this thread are focusing on the difficulties of this scheme, but UTC 
has had significant success as well. Nobody would be trying to build on top of 
it if this were not true. One reason UTC has succeeded is because of its design 
implementing Universal Time, not in spite of it.

It seems bizarre to have to state that it would be wise to fully analyze civil 
timekeeping engineering requirements before making any changes. Some here have 
participated in a variety of meetings and discussions with this goal, but I am 
unaware of any external funding for such activities. Other communities have 
invested much greater time (so to speak) and money regarding similarly 
ubiquitous, yet esoteric, standards and protocols.

If the precision timekeeping community had adopted the proposal from the 2003 
Torino symposium to define the new time scale called TI, we would have had 17 
years to cover the Earth like locusts. Instead the intervening period has been 
squandered trying unnecessarily to undermine UTC. Recipe for success:


  1.  Define a new time scale and leave UTC alone for future compatibility. 
Your own systems engineering requirements likely include time-of-day.
  2.  There are two kinds of time and timekeeping. All successful systems 
engineering will start from this simple fact.

Whatever POSIX does with leap seconds should be in a larger and more coherent 
global concept of timekeeping.

Rob Seaman
University of Arizona
--
http://hanksville.org/futureofutc/

(If you hit a stale link, replace 
“www.cacr.caltech.edu” with 
“hanksville.org” in the URL.)

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