[LEAPSECS] NIST UT1 NTP server results

John Hawkinson jhawk at MIT.EDU
Fri Jul 22 16:47:16 EDT 2016

"Mike" <mike at lumieresimaginaire.com> wrote on Fri, 22 Jul 2016
at 22:21:08 +0200 in <bec8a6a992cdbd21bb47efe68a5797d8 at lumieresimaginaire.com>:

> 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.

On June 28, Judah Levine and NIST announced via the IERS Message list
that NIST's UT1 ntp-based time service would be open access beginning
in July 2016. Announcement reproduced below.

I found your email fairly confusing.

--jhawk at mit.edu
  John Hawkinson

Message-ID: <25948628.481467094028650.JavaMail.cmadmin at gsb50ml1.ffm.web>
Date: Tue, 28 Jun 2016 08:07:08 +0200
From: <central_bureau at iers.org>
To: <messages at iers.org>
Subject: IERS Message No. 303: NIST UT1 Internet Time Service

IERS Message No. 303                                       June 28, 2016

NIST UT1 Internet Time Service

The Time and Frequency Division of NIST operates an Internet time server
that transmits UT1 time in the Network Time Protocol (NTP) format. The
server is synchronized to UTC(NIST) by a direct connection to a local
cesium standard. The offset between UT1 and UTC is added to the reply to
a query for the time. The time difference between UT1 and UTC is
obtained from IERS Bulletin A, and the value used by the time server
changes every day at 0 h UTC. The time step at 0 h UTC is generally
about 1-2 ms. This time step is generally too small to be detected by
most users.

The accuracy of the time at the server is approximately 4 ms, and is
determined by the uncertainty in the prediction of the difference
UT1-UTC in the IERS Bulletin A. The accuracy of the time received by a
user will usually be limited by the stability of the network delay from
the user's system to the time server. The overall accuracy of the time
as received by a user will generally be better than 10 ms, and will
often be significantly better than this value.

The name of the server is ut1-time.colorado.edu and its address is The ut1 time service is currently restricted to users
who register with NIST (by e-mail to Judah.levine [at] nist.gov), but it
will be converted to open-access in July, 2016.

The NIST is the US National Institute of Standards and Technology

Questions or comments to Judah.Levine [at] nist.gov

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