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NTP managed service means that you can configure NTP settings from sipXconfig UI and relay on sipXecs for starting / stopping NTP when needed (e.g. when configuration changed and needs to be applied).
Unmanaged service
When NTP is marked as unmanaged service then sipXecs won't generate any configuration or issue any service start / stop commands. This is up to the admin, however some other system components (like phones) still need info about NTP configuration. That's why in addition to turning service in an unmanaged service, admin can also specify additional NTP servers phones or other components should default to.
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