User manual

Using the NTPTime Service
246
33002479 06 07/2008
NTP Time
Synchronization
Definitions
Term Description of Service
Local clock offset Accurate local time is maintained by adjusting the time by using a local clock offset. The local
clock offset is calculated by the formula: ( (T4 - T1) + (T3 - T2) ) / 2
The formula’s variables are:
z T1 = Time at which the NTP request is transmitted from the module
z T2 = Time at which the NTP Server receives the request (provided by the module in
response)
z T3 = Time at which the NTP Server transmits the response (provided to the module in the
response)
z T4 = Time at which the NTP Response is received by the module
Time accuracy Local Time error is < 10 ms compared to the reference NTP server:
z Typical: under 5 ms
z Worst case: <10 ms
Note:
1. Settling Time: The maximum accuracy is obtained after 2 updates from the NTP server.
2. Polling Period Dependency: The accuracy is dependent upon the polling period. Less than
10 mSec of error is guaranteed for polling periods of 120 seconds or less. To obtain the best
possible accuracy and if your network bandwidth will allow, reduce the polling period to a
small value.
3. For example, choosing a polling time of 5 seconds provides better accuracy than a time of
30 seconds.
Time zone Default format: Universal Time, Coordinated (UTC)
Optional: Configure the service to use a local time zone. For example, GMT+1 for Barcelona or
Paris
Daylight savings
time
Automatic: module adjusts time in spring and fall
Leap Second Automatic: module inserts or deletes a second
Note:
1. To compensate for the deceleration of the earth’s rotation, a leap second is inserted in the
UTC time every 18 months by an INTERNATIONAL EARTH ROTATION SERVICE (IERS).
2. Leap seconds will be inserted automatically as needed. If needed, leap seconds are inserted
at the end of the last minute in June or December, as commanded by the NTP server.