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How does timezone get set?

 
 
Matt Simpson
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      Jan 9th, 12, 7:36 PM
When an iPhone is set for automatic time setting
(Settings->General->Date/Time->Set Automatically)
how does it decide what timezone to use? Is it computed based on the
phone's location? Or does the cellular carrier tell it what time zone
it's in?

I just noticed that my iPhone has the wrong timezone when I'm at home.
It says Chicago, which is in CST. When I'm at work, about 20 miles
away, it says New York, which is in EST. (I'm actually in Kentucky, but
New York is the correct timezone. Atlanta is another city in the
available list that would be correct).

At home, the Maps app shows my correct location, so the phone knows
exactly where I am. And I'm not anywhere close to a time zone boundary.
The location that it correctly shows is solidly in Eastern, so if the
phone knows where I am, it should know what time zone I'm in, unless
something else is lying to it.

Obviously, I'm being served by a different cell tower at home. So if
the phone is accepting the timezone from the cell carrier, maybe AT&T
just doesn't know where its tower is.
 
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nospam
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      Jan 9th, 12, 8:24 PM
In article
<(E-Mail Removed)-september.org>, Matt
Simpson <(E-Mail Removed)> wrote:

> When an iPhone is set for automatic time setting
> (Settings->General->Date/Time->Set Automatically)
> how does it decide what timezone to use? Is it computed based on the
> phone's location? Or does the cellular carrier tell it what time zone
> it's in?


cellular networks send the time & timezone.

> I just noticed that my iPhone has the wrong timezone when I'm at home.
> It says Chicago, which is in CST. When I'm at work, about 20 miles
> away, it says New York, which is in EST. (I'm actually in Kentucky, but
> New York is the correct timezone. Atlanta is another city in the
> available list that would be correct).


odd. does this happen with other cellphones (friends, coworkers, etc.),
including android dumbphones and other iphones?

> At home, the Maps app shows my correct location, so the phone knows
> exactly where I am. And I'm not anywhere close to a time zone boundary.
> The location that it correctly shows is solidly in Eastern, so if the
> phone knows where I am, it should know what time zone I'm in, unless
> something else is lying to it.
>
> Obviously, I'm being served by a different cell tower at home. So if
> the phone is accepting the timezone from the cell carrier, maybe AT&T
> just doesn't know where its tower is.


it could be at&t. the time they send is usually off by up to a minute,
sometimes more, so it wouldn't surprise me if the time zone was wrong.
i've seen time zone problems when daylight saving time changes, but
usually for no more than a few hours.
 
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Wes Groleau
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      Jan 10th, 12, 2:17 AM
On 01-09-2012 14:24, nospam wrote:
> it could be at&t. the time they send is usually off by up to a minute,
> sometimes more, so it wouldn't surprise me if the time zone was wrong.


Every time I've checked (not very often), my AT&T iPhone is about three
seconds off.

--
Wes Groleau

A child’s funeral
http://Ideas.Lang-Learn.us/barrett?itemid=1583
 
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nospam
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      Jan 10th, 12, 2:23 AM
In article <jeg3jj$deo$(E-Mail Removed)>, Wes Groleau
<(E-Mail Removed)> wrote:

> > it could be at&t. the time they send is usually off by up to a minute,
> > sometimes more, so it wouldn't surprise me if the time zone was wrong.

>
> Every time I've checked (not very often), my AT&T iPhone is about three
> seconds off.


my at&t phone is usually about 20-30 seconds off. not a huge deal, but
it's still wrong. sprint & verizon, on the other hand, are exact (they
have to be).
 
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Wes Groleau
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      Jan 10th, 12, 2:27 AM
On 01-09-2012 20:23, nospam wrote:
> my at&t phone is usually about 20-30 seconds off. not a huge deal, but
> it's still wrong. sprint& verizon, on the other hand, are exact (they
> have to be).


Been a couple of years since I told Sprint to get out of my life, but
back then, they were always two or three minutes.

Probably a geographic difference.

--
Wes Groleau

“There are more people worthy of blame
than there is blame to go around."
 
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Chris Blunt
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      Jan 10th, 12, 7:06 PM
On Mon, 09 Jan 2012 20:17:39 -0500, Wes Groleau
<(E-Mail Removed)> wrote:

>On 01-09-2012 14:24, nospam wrote:
>> it could be at&t. the time they send is usually off by up to a minute,
>> sometimes more, so it wouldn't surprise me if the time zone was wrong.

>
>Every time I've checked (not very often), my AT&T iPhone is about three
>seconds off.


I get similar results to you. I often check my iPhone time against the
Greenwich Time Signal broadcast on the radio station I listen to in
the mornings, and its always correct to within a second or two. It
would be interesting to know the reference source against which the
iPhone calibrates its clock.

Chris
 
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Wes Groleau
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      Jan 11th, 12, 3:08 AM
On 01-10-2012 13:06, Chris Blunt wrote:
> the mornings, and its always correct to within a second or two. It
> would be interesting to know the reference source against which the
> iPhone calibrates its clock.


It's set by a signal from AT&T via whatever tower your close to.

--
Wes Groleau

People would have more leisure time if it weren't
for all the leisure-time activities that use it up.
— Peg Bracken
 
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Wes Groleau
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      Jan 11th, 12, 3:09 AM
On 01-10-2012 13:06, Chris Blunt wrote:
> I get similar results to you. I often check my iPhone time against the
> Greenwich Time Signal broadcast on the radio station I listen to in


P.S. There's a free app called Emerald Time (I think that's the name)
that will use NTP to show how far off your phone is.

--
Wes Groleau

People would have more leisure time if it weren't
for all the leisure-time activities that use it up.
— Peg Bracken
 
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Chris Blunt
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      Jan 11th, 12, 10:46 PM
On Tue, 10 Jan 2012 21:08:44 -0500, Wes Groleau
<(E-Mail Removed)> wrote:

>On 01-10-2012 13:06, Chris Blunt wrote:
>> the mornings, and its always correct to within a second or two. It
>> would be interesting to know the reference source against which the
>> iPhone calibrates its clock.

>
>It's set by a signal from AT&T via whatever tower your close to.


Are you sure? I'm several thousand miles away from the nearest AT&T
tower.

I assume you mean it's set by the mobile network operator, which is
the method by which many other cellphones adjust their time. I'm a bit
reluctant to believe this is the way the iPhone does it because I have
another (Nokia) phone operating on the same network which is also set
to adjust it's time automatically but is consistently several seconds
out. If both phones were obtaining their time reference from the
mobile network you would expect them to have the same degree of error.

I was wondering if perhaps the iPhone uses a NTP time reference source
when it has an active internet connection available.

Chris
 
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nospam
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      Jan 11th, 12, 11:00 PM
In article <(E-Mail Removed)>, Chris Blunt
<(E-Mail Removed)> wrote:

> I was wondering if perhaps the iPhone uses a NTP time reference source
> when it has an active internet connection available.


it's from the cellular network.

it *should* use ntp, but doesn't. if it did, wifi-only devices such as
ipads and ipod touches could maintain an accurate time rather than
drift. i've seen my ipad grow to several minutes off until i sync it at
which point it gets updated from the computer's time.
 
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