[time-nuts] How are iPhones' clocks set under LTE?

[Bill Dailey]

For informational purposes I will show what I use to compare with my stock Iphone.  It is an app called emerald time.  Screenshot at: https://www.dropbox.com/s/zt6tjrsylrrtrc3/2014-08-04%2008.06.02.png

You can set it up to sync with you own ntp server.  I think. You can just spot check it.  

I have never done a rigorous analysis but it appears to be within 1.5s or better most of the time.

Doc



Sent from mobile

> On Aug 4, 2014, at 7:38 AM, BIll Ezell <wje at quackers.net> wrote:
> 
> LTE does support the long-standard NITZ (network information and time zone) service. It's an easy way to find out just where you are without having to change your TZ settings constantly. In fact, if you go to time settings on HTC Android phones, the 'automatic time update(NITZ)' setting turns on NITZ syncing. iPhones also use NITZ, as do most 3G or LTE phones. But, not necessarily for time.
> 
> NITZ implementation is carrier-optional, although almost all do support it. I know that Vodafone-Austrailia and a handful of other carriers at least at one point didn't support it. Additionally, the standard doesn't specify how accurate the time has to be, and it varies widely across providers. It's usually within a few seconds, but this isn't a high-precision time reference and can be off by minutes. But, a phone can use the timezone information to then localize time from some other time service.
> 
> An alternative to determine what your physical location location is uses lower-level information such as the ECGI (extended cell group identity) or location information from the MME (Mobile Management Entity). Don't you just love telecom? Everything's an acronym and frequently an acronym^2 or ^3.
> Anyway, the phone then looks up the physical location from whatever id it uses, then uses a time service to get the actual time, then localizes it based on the physical location.
> 
> Clearly, just using something like NTP directly isn't all that useful because you have to know your physical location to know what timezone correction to apply.
> 
> I work on cell infrastructure, mostly 3G and LTE (Ericsson), and it just amazes me that phones work at all. It is incredibly complicated and convoluted.
> 
>> Unlike CDMA (where time distribution was an automatic part of the
>> low-level protocol) I suspect the time displayed on many modern phones is
>> not set by the telephony synchronous protocol but rather by IP-over-Wifi
>> packets.
>> 
>> And the packets don't seem to do a very effective job keeping the clock
>> ont he phone correct. My employer gave me a Nokia Lumia 630 "Windows Phone"
>> and its clock has always been off by at least a minute.
>> 
>> There was a few years ago, a very nice article about the effort to repair
>> the clocks in clock towers in many cities. What rang most true to me was
>> "if you visit a town they can't even keep the clock correct, who else knows
>> what else is wrong there?".
>> 
>> Tim N3QE
> 
> -- 
> Bill Ezell
> ----------
> The day Microsoft makes something that doesn't suck
> will be the day they make vacuum cleaners.
> 
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