[time-nuts] Striking change in iPhone time accuracy with 8.2

Oz-in-DFW lists at ozindfw.net
Wed Apr 1 16:41:07 EDT 2015


On 4/1/2015 2:31 PM, Paul wrote:
> On Wed, Apr 1, 2015 at 12:33 PM, Reid Oda <reid.oda at gmail.com> wrote:
>
>> This seems to imply that the iPhone does get sub-second timing info from
>> GPS. Can anyone confirm/deny this?
>>
> As of iOS N where I believe N == 5 it does the equivalent of calling
> ntpdate every few hours if the network is available.  I assume it uses the
> mobile system if the network is unavailable and you have a cellular radio
> because the devices (can) have a lot of drift.
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The phone has to keep synch within a few microseconds of the network.  
There was a time when operators were very sloppy about clock time and 
really only worried about network frequency, but most operators are now 
maintaining 50 ns or so at the base stations and have to maintain within 
5 microseconds to meet the LTE specs.  How much of this is preserved 
through to the user interface is anyone's guess.

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