Gorgy Timing LEDI Network IN - Page 56

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MDE-LEDI-NETWORK-IN-4065V1.0
To perform this synchronization, the NTP client software permanently compares the two
clocks and computes the following information:
Offset: ►
It’s the difference between the time of the server clock and the time of the client
clock. For example, if the server clock indicates 2:10:13 and the client clock indica-
tes 2:11:14, the offset is –1:01.
Drift: ►
It’s the frequency difference between the two clocks. When drift is not null and
without clock correction, the offset between the two clock increase or decrease
depending on the drift sign.
3
The following gure shows how the evolution of the two clocks with or without drift:
The objective of the synchronization of a NTP client to a NTP server is to reduce as
much as possible the drift and the offset. The accuracy and stability of the client clock
is tightly coupled to the efciency of the reduction process.
3/ There are several reasons for the presence of a drift between two clocks: generally the drift is due to the tempe-
rature difference between the two clocks.
Heure serveur
Heure client
Heure serveur
Heure client
Heure serveur
Heure client
Heure serveu
r
Heure client
Dérive nulle
Dérive constante
Evolution dans le temps
server time
client time
server time
client time
server time
client time
server time
client time
Drift is null :
Drift is constant :
Evolution during time
1. INTRODUCTION