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

[Brian Garrett]

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