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Leap Second Certification

The International Earth Rotation and Reference Systems Service (IERS), the organization responsible for measuring the relationship between UTC (Coordinated Universal Time) and the rate of Earth’s rotation, sent out Bulletin C36 announcing that a positive leap second would be introduced at the end of the day on December 31, 2008. 
 
The leap second insertion increases the length of the last minute of the UTC day to 61 seconds. The sequence of dates of the UTC second markers shall be:

  • 2008 December 31, 23h 59m 59s
  • 2008 December 31, 23h 59m 60s
  • 2009 January 1, 0h 0m 0s

Reason for the Leap Second
Until 1967 the base unit for time keeping, the second, was defined based on the earth’s rotation around the sun: one second was equal to 1/86400 of a mean solar day. The duration of the earth’s orbit around the sun varies year after year and thus the definition of a second based on the earth’s rotation could also theoretically change year after year. This definition of a second was eventually found to not provide adequate precision for the scientific community.

By 1967, the world’s timekeepers decided to redefine a second to be based on atomic principles, which are much more accurate than the earth’s rotation around the sun and are much easier to reproduce with a high level of precision. From that point on, a second was defined as:

9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

With the definition of a second now a function of atomic properties the world’s timekeepers needed a way to add or remove seconds in order to keep the world’s clocks in sync with the earth’s rotation. The addition or removal of seconds is known as a leap second.

Leap seconds don’t happen every year but rather only when the difference between the earth’s atomic clocks (UTC) and the mean solar time (UT1) approaches 0.9 seconds. The last leap second was added on December 31, 2005. 
 
The Handling of Leap Seconds by Symmetricom
In 2005, Symmetricom completed simulation testing of all of our time and frequency receivers, time and frequency processor modules and network time servers to characterize their behaviors and then appropriately distribute the leap second information. This included both current and legacy products. 
 
For the 2008 leap second insertion, Symmetricom has completed simulations on its products that were not tested during the 2005 leap second insertion as well as other key products. These results are as follows:

Time & Frequency Receivers

XLi GPS Time & Frequency Receiver (PDF)
XL-GPS Time and Frequency Receiver (PDF)
XLi SAASM GB-GRAM Time and Frequency Receiver (PDF
4370A DVB Sync Source (PDF)


Network Timing

SyncServer® S200 GPS Network Time Server (PDF)
SyncServer® S250 GPS Network Time Server (PDF)
SyncServer® S300 GPS Network Time Server (PDF)
SyncServer® S350 GPS Network Time Server (PDF)

Bus Level Timing

bc627AT PC Time & Frequency Processor (PDF)

 

For additional information on Telecom Solutions Division (TSD) products, please refer to the Field Service Bulletin section of the support website. 

2005 Leap Second Insertion

Results from the leap second testing that was done for the 2005 leap second insertion can be found below:
 
Time & Frequency Receivers


Time & Frequency Distribution


Network Timing


Bus Level Timing


Telecom Products

 
OEM Subsystems