[time-nuts] Re: Where do people get the time?

[John Hawkinson]

On Tue, Dec 28, 2021 at 2:29 AM Hal Murray <halmurray at sonic.net> wrote:
> jhawk at alum.mit.edu said:
> > every few months websites stop working and I look and it's bceuase
> > the date has been reset back to 2011 or 2003 and so SSL certificate validity
>
> What does "sync time to the network" mean?  What software is doing the syncing
> and where is it getting the time?
>
> Is the source of time something like NTP that user code could monitor or is it some undocumented back door tangled with the cell phone stuff?

I feel like tvb is lurking waiting to tell us that this is not a
time-nuts topic, and it's more like a "people who have no idea why
their clocks are trash and if you can't measure the Allen deviation we
shouldn't be talking about it take it to time-no-nuts" topic.

That said, on my Android phone, this is Settings > Date and Time >
Automatic Date and Time which is labeled, "Use the date, time, and
time zone provided by your network. Turn off this function to set the
date, time, and time zone manually." This text suggests it is not NTP,
since ntp does not provide timezones. And it doesn't seem terribly
likely that NTP would behave in this fashion, although I suppose it is
not inconsistent with ntp against some element of the local cell that
has the wrong time.

https://source.android.com/devices/automotive/time/automatic_time_detection
suggests the situation is fairly complicated and quite possibly
carrier/vendor/ovrerlay-specific, and my attempts to find actual
source code were not successful.

My vague recollection of this is that disabling the cellular network
(i.e. airplane mode) and using wifi does not resolve the problem,
which also suggests the phone isn't using NTP; but usually when this
problem occurs it's a higher priority to work around and set the time
manually than it is to do serious diagnostics on behavior, so my
memory is dim.

I don't think that a phone getting time from the cellular network is
properly characterized as using an "undocumented back door tangled
with the cell phone stuff," but yeah, I think getting time from the
cell phone network is "cell phone stuff" and it's not obviously
documented, but it's also kind of a front door.

--
jhawk at alum.mit.edu
John Hawkinson