How does timezone get set?

Discussion in 'iPhone' started by Matt Simpson, Jan 9, 2012.

  1. Matt Simpson

    Matt Simpson Guest

    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.
     
    Matt Simpson, Jan 9, 2012
    #1
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  2. Matt Simpson

    nospam Guest

    In article
    <-september.org>, Matt
    Simpson <> 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.
     
    nospam, Jan 9, 2012
    #2
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  3. Matt Simpson

    Wes Groleau Guest

    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
     
    Wes Groleau, Jan 10, 2012
    #3
  4. Matt Simpson

    nospam Guest

    In article <jeg3jj$deo$>, Wes Groleau
    <> 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).
     
    nospam, Jan 10, 2012
    #4
  5. Matt Simpson

    Wes Groleau Guest

    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."
     
    Wes Groleau, Jan 10, 2012
    #5
  6. Matt Simpson

    Chris Blunt Guest

    On Mon, 09 Jan 2012 20:17:39 -0500, Wes Groleau
    <> 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
     
    Chris Blunt, Jan 10, 2012
    #6
  7. Matt Simpson

    Wes Groleau Guest

    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
     
    Wes Groleau, Jan 11, 2012
    #7
  8. Matt Simpson

    Wes Groleau Guest

    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
     
    Wes Groleau, Jan 11, 2012
    #8
  9. Matt Simpson

    Chris Blunt Guest

    On Tue, 10 Jan 2012 21:08:44 -0500, Wes Groleau
    <> 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
     
    Chris Blunt, Jan 11, 2012
    #9
  10. Matt Simpson

    nospam Guest

    In article <>, Chris Blunt
    <> 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.
     
    nospam, Jan 11, 2012
    #10
  11. Matt Simpson

    Alan Browne Guest

    On 2012-01-11 16:46 , Chris Blunt wrote:

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


    It's not clear to me.

    I have an App called Time which allows me to enter an ntp address (so I
    use one nearby). It's not clear if this changes the system ntp or is a
    separate process using a separate ntp server while the iPhone uses its own.

    Generally Mac's come set to the super regional Apple ntp server.
    (time.apple.com, time.asia.apple.com, time.euro.apple.com). I assume
    the iPhone uses those same defaults. (I set my Mac to a local one).

    --
    "We demand rigidly defined areas of doubt and uncertainty."
    Douglas Adams - (Could have been a GPS engineer).
     
    Alan Browne, Jan 11, 2012
    #11
  12. Matt Simpson

    JF Mezei Guest

    Alan Browne wrote:

    > I have an App called Time which allows me to enter an ntp address (so I
    > use one nearby). It's not clear if this changes the system ntp or is a
    > separate process using a separate ntp server while the iPhone uses its own.



    If you read the docunention, it is clearly wirtten that because IOS does
    not allow an application to change the time, the "Time" application does
    not change the iphone's time. It mereley reports the offet to the reat
    (ntp obtained) time.
     
    JF Mezei, Jan 11, 2012
    #12
  13. Wes Groleau <> 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.


    Emerald time is good. But it ony reports using NTP how out the Iphone
    is. Travelling to/from different time zones via the channel tunnel, I
    was badly caught out several times by the Iphone not changing time zone
    properly. THERE IS A BUG SOMEWHERE. But I was not able to pin down what
    was going on. In some cases as I roamed about within Europe I could see
    the clock jump as I roamed to different networks. I suspect there is a
    glitch within IOS which stops the Iphone from properly interpreting what
    is being sent out by the local tower.
     
    Fergus McMenemie, Jan 16, 2012
    #13
  14. Matt Simpson

    nospam Guest

    In article <1kdzfoo.1oqq4pq14ggjg8N%>, Fergus
    McMenemie <> wrote:

    > Emerald time is good. But it ony reports using NTP how out the Iphone
    > is. Travelling to/from different time zones via the channel tunnel, I
    > was badly caught out several times by the Iphone not changing time zone
    > properly. THERE IS A BUG SOMEWHERE. But I was not able to pin down what
    > was going on. In some cases as I roamed about within Europe I could see
    > the clock jump as I roamed to different networks. I suspect there is a
    > glitch within IOS which stops the Iphone from properly interpreting what
    > is being sent out by the local tower.


    the only glitch is that apple does not understand time zones. macs have
    time zone issues too.
     
    nospam, Jan 16, 2012
    #14
  15. Matt Simpson

    Wes Groleau Guest

    On 01-16-2012 16:48, Fergus McMenemie wrote:
    >> > 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.

    > Emerald time is good. But it ony reports using NTP how out the Iphone


    That's what I said.

    --
    Wes Groleau

    People would have more leisure time if it weren't
    for all the leisure-time activities that use it up.
    — Peg Bracken
     
    Wes Groleau, Jan 17, 2012
    #15
  16. Matt Simpson

    Dillon Pyron Guest

    Thus spake nospam <> :

    >In article <jeg3jj$deo$>, Wes Groleau
    ><> 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).


    My AT&T iPhone, AT&T home phone (not Uverse), my TW cable box and my
    Vista laptop all disagree by about 45 seconds. Never consistently!

    I "trust" my laptop the most. It is consistenly late from my GPS,
    which I credit as the most "accurate" and "precise". When I have 6 or
    more sattelites in view.

    It depends on the delays from the source to the transmitter to you.

    Any Unix sysdamins out there? My answer to most questions of "can
    you?" or "why does it?" is almost always "it depends". I was told
    long ago in SunOS school that that is the correct answer. Unless it's
    a multiple choice question. The it's "yes".
    --

    - dillon I am not invalid

    So Kim Jung Ill shows up at the barbecue. "Wait,"
    says Qadaffi, "you don't have any peircings." "If you
    starve your people enough they'll be too weak to rebbel."
    "You have the same number of holes in your head as when
    you were born," says bin Laden. "My compound had radar
    and antiacraft misslles." "Your neck," shouted Hussein,
    "it's the same length." "I didn't piss on W's father."
    "Then what happened?" the three asked. "Damned counterfiet
    Lipitor and insulin!"
     
    Dillon Pyron, Jan 18, 2012
    #16
  17. Matt Simpson

    Matt Simpson Guest

    Back to my original question, which involved the timezone and not the
    precise time, it gets curiouser and curiouser.

    I'm not completely convinced that the cell tower is telling the iPhone
    what timezone it's in. Or to be more correct, maybe the cell tower is
    telling it, but the iPhone is ignoring that in favor of some other
    source.

    For one thing, I've noticed that the timezone doesn't change immediately
    when I get home. It stays correct for a while. It seems to change
    overnight.

    Also, the displayed time doesn't seem to change zones while the screen
    is locked. When I picked up my phone this morning, it had the correct
    time. As soon as I unlocked the screen, the time dropped back an hour.

    After being at work about an hour, I noticed the time displayed on the
    locked screen was still an hour behind. I unlocked the screen and it
    immediately jumped ahead.

    There's something very mysterious happening overnight that's causing my
    phone to think it's in a different timezone. At this point, I'm not
    even sure it's related to location. I haven't spent a night with the
    phone somewhere else to see if it changes timezones elsewhere.
     
    Matt Simpson, Jan 19, 2012
    #17
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