[time-nuts] NIST UT1 NTP server results
michael.cook at sfr.fr
Fri Jul 22 16:59:31 EDT 2016
I have started a new thread for this just in case anyone wants to comment and added a link to the stats plot as the png got removed from the first post.
This really has more to do with timescale distribution rather than leap seconds but the fact that NIST put together a UT1 NTP server in the first place is tightly connected to the leap second controversy. So I have also published this over at the leap second list and prefer that any follow up is done over there.
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 <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 peerstat 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 jitter
+192.168.1.23 .GPS. 1 u 61 64 377 0.173 -0.014 0.024
22.214.171.124 .NIST. 1 u 41 64 377 130.670 -225.01 0.102
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 requests.
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.
See it at < http://stratum1.ddns.net:8080/timenuts-data/peerstats17677_126.96.36.199.png >
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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