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

Bob Bownes bownes at gmail.com
Mon Aug 4 00:38:33 EDT 2014


Well, I seem to remember finding NTP running on my jail broken iPhone. But that was a few years ago. 

> On Aug 3, 2014, at 17:41, Tim Shoppa <tshoppa at gmail.com> wrote:
> 
> 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
> 
> 
> On Sun, Aug 3, 2014 at 4:37 PM, Brian Garrett <garrettbrian1960 at gmail.com>
> wrote:
> 
>> Hi all,
>> 
>> First “time”r here.  This may not rank up there with your degree of
>> time-nuttery, but I haven’t been able to get an answer elsewhere.  Recently
>> I was discussing the issue of how the different cellular providers set
>> their time, and I told him that I’d read that CDMA phones and towers have
>> to have their clocks synced to GPS as part of the protocol, whereas GSM
>> phones do not, and can theoretically be set to wall time, and thus phones
>> on networks using CDMA would have atomic accuracy all the time since what
>> they were getting was as good as GPS.
>> 
>> Well, obviously I was pathetically behind the times.  Most everybody these
>> days including Verizon, which both I and my friend have now, uses LTE , as
>> you know.  I have looked all over for info as to what LTE’s time-setting
>> requirements are, as implemented by Verizon, but I’ve not seen discussions
>> of it anywhere.  I’ve seen amusing anecdotes over what can happen if your
>> Android isn’t set to receive the network’s time, or what can happen to your
>> phone’s clock if you live near a time zone boundary, but no discussion of
>> how time dissemination is handled in-network.  I know my iPhone can be, and
>> usually is, 2 or 3 seconds fast or slow when checked against an accurate
>> reference clock, so I’m thinking they can just use wall time like GSM did.
>> 
>> Has this been discussed on the list before?  I haven’t seen anything in
>> the archives, and no-one at Verizon that we of the unwashed masses have
>> access to will know the answer  Pointers, anyone?
>> 
>> 
>> Thanks in advance,
>> Brian
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