3.2.4. Configuration recommendations
To comply with legal time, if there is no indicator on the time input of an LEDI
®
Network TDS,
check in the latest IERS Bulletin C if a leap second will be inserted in June or December at
least one month in advance and configure the manual indicator on this product accordingly.
Certain NTP clients refuse to synchronise with servers that do not provide a leap second
indicator. On these NTP servers, the manual indicator must therefore be configured and its
return to 0 at insertions (by default it is disabled at insertions) in order to the clients to
synchronise.
3.3. SYNCHRONISATION CONCEPTS
Synchronisation refers to the process of setting a local clock (known as “internal”) by aligning
the information with a distant clock (the “reference”).
A local clock runs using a reference frequency, created by an oscillator. The LEDI
®
NETWORK TDS integrates a temperature-compensated oscillator (TCXO).
In order to achieve this synchronisation, the device which is to be synchronised (called the
client) compares its clock with that of a reference device (called the server) and calculates
the following information:
► Offset: this is the instantaneous difference between the client’s time and the server’s
time. For example, if the server indicates 2:10:13 and the client displays 2:11:14, the
offset is 1:01.
► Drift: this is the difference in frequency between the two clocks. If not corrected, the
offset between the two clocks is constantly increasing or decreasing.
The following diagram shows how the two clocks evolve with or without drift:
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