News from 2015-03-25


Leap Second 2015: Important Information for Meinberg Customers


Early in 2015 the IERS announced in their Bulletin C publication that a leap second will be inserted at the end of June. For users of NTP (and other time synchronization technologies) there are a number of things that should be checked in order to prepare for this event.


Update: After further tests, we strongly recommend to update the leapsecond file on LANTIME V6.x systems - see "Leap Second Update for 6.x" below.

Update 2: LANTIME systems running V4.x or V5.x firmware versions start on June 1st to announce the upcoming leapsecond in their NTP responses which is correct according to RFC 5905.

Introduction

Introducing a leap second is necessary to ensure that the difference between the coordinated universal time (UTC) to the astronomical time scale is within a small range. UTC is the base of the time zones that are commonly used and it is determined with the help of atomic clocks which are installed in a lot of different locations. Most of these atomic clocks are operated by national metrology organisations, for example the US National Institute of Standards and Technology (NIST), the National Physical Laboratory in the UK or the German Physikalisch-Technische Bundesanstalt (PTB). More background information about the leap second and the UTC timescale can be found on websites which we listed in the "Weblinks" section below.

A leap second will always be inserted after 23:59:59 (UTC), typically either on Dec 31st or June 30th (although other dates are theoretically possible, they have not been used so far).

Leap second Handling by Meinberg Products

Some time transfer protocols or technologies can pre-announce a leap second in order to enable the receiver of the time information to prepare for a leap second insertion and to ensure that the leap second event is correctly handled even if the receiver looses the connection to its time reference before the leap second insertion actually needs to happen. Time synchronization is possible only with the help of time transfer, i.e. transmitting the correct time from a reference source to one or more receivers. The receivers then compare their own clock with the time information they received from the reference and adjust their time accordingly.

LANTIME Time Server Appliances

A number of network protocols have been designed to allow time transfer between nodes connected to a network. The most popular and widely used is NTP (Network Time Protocol), that has been published as an RFC in its current revision 4 by the IETF: RFC5905.

Another time sync protocol is the Precision Time Protocol (PTP), that has been published as IEEE Standard 1588 in its current form in 2008 (IEEE 1588-2008).

Other time transfer protocols are either outdated (Time, daytime) or their use is limited to special application environments. This document therefore only covers NTP and PTP.

Network Time Protocol (NTP) Servers

A leap second is announced with a flag ("leap bit") within the NTP response that an NTP server sends to an NTP client. This flag can only be activated on the day of the leap second event. For this years' leap second, a LANTIME NTP server would not start to announce the leap second in its NTP responses before 00:00:00 (UTC). Most likely the announcement will start between 23 and 1 hour before the leap second insertion at midnight UTC. After the leap second insertion has been done, the flag will be cleared. Please note that some references like DCF77 start to announce an upcoming leap second only one hour before the actual event and therefore a LANTIME NTP server can only start to announce the leap second in its NTP packets at that time.

PTP Grandmaster Clocks

The Precision Time Protocol also defines leap second announcement. Just like NTP the protocol implements the announcement in a way that allows to annouce the event only on the day when it actually happens. The PTP Grandmaster sets a flag in its ANNOUNCE messages and in LANTIME devices this starts around 1 hour before the leap second event.

Leap Second Update Files for LANTIME Firmware

LANTIME systems run different versions of the NTP reference implementation and the Meinberg PTP stack. You can find out the firmware version of your device on the main page of the web UI. If you are unable to identify the version your LANTIME firmware or if you are unsure which version you are running, please contact your Meinberg support.

LANTIME Firmware Versions 3.x and older

These firmware versions have not been changed since more than 10 years. If you still run such a device, please contact Meinberg support to check whether it is required to take further action for the upcoming leap second. Meinberg has currently no knowledge about any problems with leap seconds but we are happy to assist you with running tests, if you are unsure whether your LANTIME system is ready for the leap second.

LANTIME Firmware Versions 4.x and 5.x

As part of the free lifetime support program we offer a small update for both firmware generations 4 and 5 which contain an updated NTP leap second file to ensure proper handling of the 2015 leap second. In general, on LANTIME systems using a radio signal like GPS or DCF77 as their primary reference the leap second announcement is received automatically and processed correctly by the system. However, we do recommend to install an up-to-date leap second file in order to ensure that the leap second is inserted when no radio signal is available. LANTIME systems using reference sources that do not provide leap second announcements (for example PPS and IRIG) have to install the update in any case. Please note that the NTP version running on V4 and V5 systems will start to announce the upcoming leap second on June 1st, which is permitted by RFC 5905 as the leap indicator bit refers to the "last day of the month".

The NTP versions on V4.x and V5.x LANTIME systems require to enable autokey to accept a leap second file:

Generate new NTP public key
Step 1: Generate Autokey - "Web Interface - Security - NTP autokey generation - Generate new NTP public key"

On the NTP page of the web UI you have to tick the "Autokey" checkbox to activate this:

Select Active Autokey
Step 2: Activate Autokey - "Web Interface - NTP management - NTP configuration - Select Active Autokey"

NOTE: All M-Series LANTIME models running V5.x (M100, M200, M300, M400, M600, M900) are compatible with V6.x, we therefore strongly recommend that you upgrade your M-Series LANTIME systems to the latest V6.16.x stable version. As the firmware update will include the latest leap second file, you do not have to install the update below if you decide to upgrade to a 6.x version.

Leap Second Update for V4.x
Download: 2015-06-leapsecond-v4.tgz

Installation: Install the update file by logging into the Web UI and using the "LANTIME firmware update" function on the "Local" page. The NTP service needs to be restarted afterwards to apply the changes. This is automatically taken care of by the update process and you have to be aware that the NTP service will become unavailable for a short period of time.

Leap Second Update for 5.x
Download: 2015-06-leapsecond-v5.upd

Installation: Install the update file by logging into the Web UI and using the "LANTIME firmware update" function on the "Local" page. The NTP service needs to be restarted afterwards to apply the changes. This is automatically taken care of by the update process and you have to be aware that the NTP service will become unavailable for a short period of time.

LANTIME Firmware Versions 6.x

All V6 firmware versions will handle the leap second event correctly when they are synchronized by a radio signal carrying leap second announcements, for example GPS, GLONASS or DCF77. However, we recommend to install the provided leap second update to ensure that the leap second insertion is correctly performed even in the absence of a valid radio signal. LANTIME systems using reference sources that do not provide leap second announcements (for example PPS and IRIG) have to install the update in any case.

NOTE: Firmware 6.16.x versions from 6.16.008 as well as Firmware 6.17.x versions from 6.17.006 already include the latest leap second file and therefore it is not required to install the leap second file update on these machines.

Leap Second Update for 6.x
Download: 2015-06-leapsecond-v6.upd

Installation: Install the update file by logging into the Web UI and using the "Firmware/Software Update" function on the "System" page. The NTP service needs to be restarted afterwards to apply the changes. This is automatically taken care of by the update process and you have to be aware that the NTP service will become unavailable for a short period of time. After the update has been installed, the update script will ask you to reboot the server. This is not required, you can therefore ignore this request and simply return to the main page of the Web UI.

Meinberg Bus Level Products - ISA, PCI, PCI-X, PCI-Express and USB

The leap second insertion is handled correctly by all Meinberg bus level products which use a radio signal (GPS, DCF77, GLONASS) as their time reference. The PTP270PEX PTP slave PCIe card processes a leap second announcement sent by a PTP Grandmaster. PCI and PCIe slot cards and USB devices using IRIG as their reference could go into an unsynchronized state during and shortly after the leap second insertion but will automatically resynchronize afterwards.

If you have any questions, please contact Meinberg Technical Support providing the serial number and, if available, the firmware and driver versions of your Meinberg bus level products.

Other Meinberg GPS- and PZF-Reference Clocks

The rackmount (BGT and MP models) and railmount (HS) Meinberg reference clocks have no known problems in regards to leap second events. However, if you have any questions, please contact Meinberg Technical Support providing the serial number and, if available, the firmware and driver versions of your Meinberg products.

Windows NTP

The NTP Versions 4.2.4p5 and newer correctly process leap second announcements from upstream NTP servers. We do recommend to use the latest stable NTP version 4.2.8 which is available on our NTP for Windows Download page. Please note that a new version 4.2.8p2 covering some issues with Windows 8 is currently worked on and will be released shortly.

An existing NTP installation can be prepared for the leap second event by manually providing a leap second file. This file is provided by NIST and other organisations, including Meinberg:

To tell ntpd to use the file, it needs to be added to the ntp configuration file. For NTP 4.2.6 and newer this is possible using the "leapfile" directive:

Example:

leapfile "/path/to your/leap-file"

In NTP versions prior to 4.2.6, adding a leap second file requires a more complex procedure. Information about this can be found on the NTP documentation website doc.ntp.org and on the NTP Support website.

Leap Second Workshop

The Meinberg Sync Academy offers a leap second workshop. The seminar covers detailed background information about leap seconds and the processing of a leap second event is demonstrated in a hands-on lab for a wide range of time sync technologies like GPS, NTP, PTP and IRIG.

Weblinks


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