How UEs get Time in LTE

You may have noticed in the settings on your phone the time source can be set to “Network”, but what does this actually entail and how is this information transferred?

The answer is actually quite simple,

In the NAS PDU of the Downlink NAS Transport message from the MME to the UE, is the Time Zone & Time field, which contains (unsuprisingly) the Timezone and Time.

Time is provided in UTC form with the current Timezone to show the offset.

This means that in the configuration for each TAC on your MME, you have to make sure that the eNBs in that TAC have the Timezone set for the location of the cells in that TAC, which is especially important when working across timezones.

There is no parameter for the date/time when Daylight savings time may change. But as soon as a UE goes Idle and then comes out of Idle mode, it’ll be given the updated timezone information, and during handovers the network time is also provided.
This means if you were using your phone at the moment when DST begins / ends you’d only see the updated time once the UE toggles into/out of Idle mode, or when performing a tracking-area update.

One thought on “How UEs get Time in LTE

  1. #HowIPHONEgetsDateandTimewhenConfiguredwithSetAutomatically?

    how iphone (ios16+) gets date and time when configured with ‘set Automatically’ ? Is it from 4G carrier/(LTE service provider assuming it is on 4G) , Apple NTP SRV , GPS , assuming location services are enabled?

    And what’s the precedence order it consider – when all the above sources are available ?

    Secondly, in case of contradiction b/w time / time zone received from different sources (LTE carrier, GPS, NTP) which source will be referred? Example- carrier has set and send incorrect timezone or date to the UE , but as per GPS location received from UE (via location services) apple can see the more accurate time zone, in this case will it classify date/timezone rcvd from carrier as inaccurate and will ignore them over the one received from iphone GPS receiver data (via location services) ?

    What if a person goes out of coverage in deep basement and thus losing all sources for a while i.e. no carrier coverage, mobile data, and phone GPS receiver unable to work at that deep basement area or lifts ..

    Pls share your understanding on this topic..

    #iPhone #time #date #timezone #SetAutomatically #iOS16+ #GPS #NTP SRV #LTE #serviceprovider

    Best Regards!
    Ashish JAIN

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