GNSS Receiver (if available as an input reference): The GNSS satellite system trans-
mits information regarding a Leap Second adjustment at a specific Time and Date an
arbitrary number of months in advance.
Input references other than GNSS: Some of the other available input references
(e.g., IRIG, ASCII, NTP) can also contain pending Leap Second notification in their
data streams (see chapter below).
Manual user input: VersaSync can be manually configured with the date/time of
the next pending Leap Second. On this date/time, the System Time will auto-
matically correct for the Leap Second (unless the System Time’s timescale is con-
figured as either GPS or TAI).
3.2.3.2 Leap Second Alert Notification
VersaSync will announce a pending Leap Second adjustment by the following methods:
ASCII Data Formats 2 and 7 (among other formats) from the ASCII Data option
modules contain a Leap Second indicator. During the entire calendar month pre-
ceding a Leap Second adjustment, these Formats indicate that at the end of the cur-
rent month a Leap Second Adjustment will be made by using the character ‘L’
rather than a ‘_ ‘ [space] in the data stream. Note that this does not indicate the dir-
ection of the adjustment as adding or removing seconds. These formats always
assume that the Leap Second will be added, not removed.
NTP Packets contain two Leap Indicator Bits. In the 24 hours preceding a Leap
Second Adjustment, the Leap Indicator Bits (2 bits) which normally are 00b for sync
are 01b (1) for Add a Leap Second and 10b (2) for Remove a Leap Second. The bit
pattern 11b (3) indicates out of sync and in this condition NTP does NOT indicate
Leap Seconds. The Sync state indicates Leap Seconds by indicating sync can be
00b, 01b, or 10b.
PTP Packets provide leap indication with a 12-hour notification window.
Some IRIG formats provide leap second notification indicators.
Note: It is the responsibility of the client software utilizing either the Data
Formats or NTP time stamps to correct for a Leap Second occurrence. Ver-
saSync will make the correction at the right time. However, because com-
puters and other systems may not utilize the time every second, the Leap
Second correction may be delayed until the next scheduled interval, unless
the software properly handles the advance notice of a pending Leap
Second and applies the correction at the right time.
3.2 System Time
CHAPTER 3 • VersaSync User Manual Rev. 7.0
147
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