[LEAPSECS] NIST UT1 NTP server results

mike at lumieresimaginaire.com mike at lumieresimaginaire.com
Fri Jul 22 16:21:08 EDT 2016


    This was originally directed to the time-nuts list as it is more time 
scale oriented. However there has been quite a bit of leakage between 
the two lists following the Dec16 leap announcement, so I will post to 
both, but the discussion should stay on one list of possible, so tvb and 
I suggest it be on the leapsecs list. Sorry to those who ahve already 
received the text and no image. I have added a link here so that you can 
see the graph.

I am a rubbery seconds supporter myself. It is about time we realized 
that humans are not machines and like the idea of 86400 second days from 
here to the end of time.
There is of course a need for precise SI time intervals and a time scale 
to go with, but that can be distributed alongside an 86400sec day UTC. 
The techno exists, we just need the will to say that we humans take 
precedence. UT1 rules.

I'll jump down from my drum and share some data which I have not seen 
here before.

As most of you will already be aware, one of the results of the 
never-ending arguments about what to do with leap seconds, was that the 
IERS agreed to make available electronically UT1-UTC deltas with much 
greater precision than the GPS stream does (0.1 sec resolution). AFIK we 
don't have that yet, but at the beginning of June 2015, Judah Levine at 
NIST announced that NIST would be distributing high resolution UT1 in 
NTP frames .
See < http://www.nist.gov/pml/div688/grp40/ut1_ntp_description.cfm>.

As you can see from the document, the service was available to 
registered users with static IP addresses. My ISP only hands these out 
for $$$s so I registered with some of the cheaper VPN providers ones to 
test out the service over VPN links. Unfortunately there were such 
severe latency and jitter issues with all of those that I tried, that I 
abandoned my tests in August 2015. I also think I unfortunately pissed 
off Judah with my repeated requests for IP address registration as he 
stopped responding to mails. Sorry for that Judah if you are looking in.

Anyway I forgot all about it until the other day when I was looking at 
the peerstats data of the server I was using for the tests and 
discovered that the UT1 server was alive and responding over my 
unregistered IP with half the latency and usec level jitter. Luckily I 
had left the address in place in my ntp.conf with noselect option.
Here is the ntpq -pn data.
mike at cubieez2:~/NIST_UT1_server_data$ ntpq -pn
remote             refid   st  t when poll reach     delay   offset     
+      .GPS.   1   u   61   64   377     0.173   -0.014      
0.024    .NIST.  1   u   41   64   377   130.670 -225.01       

You will also note from the NIST document and the NIST time server 
address links, that the UT1 NTP service will not respond to unregistered 
NIST may or may not have opened the box deliberately. I don't know, but 
if you wish to use the service please at least contact Judah before 
doing so. It would be a shame to have it going deaf.

Anyway, here are the results from the data I collected.
I have graphed the UT1 server offsets reported by the NTP peerstats data 
over the last 20 days and also the observed UT1-UTC deltas from IERS 
Bulletin A and the predicted UT1-UTC deltas for the same period from 
Bulletin A.

The plot is at < 

As you can see, there is a systematic offset from the observed values 
reported in Bulletin A but the served value appears to track the 
predictions rather than the observed values. The resolution is much 
better than the 0.1s available via GPS but as the UT1 time is constant 
over the 24h day, it is not good enough to make a rubbery seconds clock. 
We need some interpolation.

The 13/14th of July something strange was going on. I was not monitoring 
this system at the time and have no idea what it was.


"The power of accurate observation is commonly called cynicism by those 
who have not got it. »
George Bernard Shaw

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