ubuntu-phone team mailing list archive

[Matthew Paul Thomas <mpt@xxxxxxxxxxxxx>]

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Tony Espy wrote on 01/08/13 16:05:
> ...
> 
> As I mentioned earlier, AFAIK, the only automatic provisioning of
> time zone information comes from a NITZ message which includes the 
> following data:
> 
> "yy/mm/dd,hh:mm:ss(+/-)tz,dt"
> 
> Furthermore, this message is never received over Wi-Fi, and AFAIK 
> doesn't require a cellular data connection.

My mistake, sorry. Fixed.
<https://wiki.ubuntu.com/TimeAndDate?action=diff&rev2=68&rev1=67>

> There are problems however with relying on just the NITZ messages. 
> First, it's not universally supported by operators. Second, some
> of the fields are optional, so it's possible that "tz" may not be 
> included in the messages.  Third, although the NITZ messages
> include "time", the accuracy is only required to be "in the order
> of minutes". See [a] for more details.
> 
> AFAIK, this is the only mechanism available to set the "time-zone" 
> automatically. Again, as mentioned before, Android has a hack that 
> attempts to set time zone automatically based upon the currently 
> registered operator in cases where NITZ is not supported and/or
> known to inaccurate.

I've abstracted this into the term "informative carrier". A carrier
might be informative if it provides full time plus accurate time zone
information itself, or if it provides only accurate time information
but you've implemented Android-like external knowledge of its time zone.

So, here's the new text:

| In the System Settings “Time & Date” panel, the “Set the time and
| date:” menu should be followed by radio items for “Automatically” and
| “Manually”, then an item with the current date and time as its label.
| These items’ state, and what follows them, should depend on three
| things: whether the current setting is “Automatically”, whether you
| have any kind of data connection, and whether you’re connected to an
| *informative carrier*, one that provides time information of known
| time zone.
|
| * If you have a data connection (cellular or wi-fi) for the phone to
| access an NTP server, or you’re connected to an informative carrier,
| then automatic time setting is currently in effect. Nothing should
| follow the items.
|
| * If you *don’t* have a data connection (cellular or wi-fi) for the
| phone to access an NTP server, *and* you’re not connected to a
| carrier at all, then automatic time setting is not currently
| possible. The items should be followed by the caption “Setting the
| time and date automatically requires a cellular or data connection.”,
| a “Cellular Settings…” button, and a “Wi-Fi Settings…” button.
|
| * If you don’t have a data connection for the phone to access an NTP
| server, and you’re connected to an ''uninformative'' carrier, then
| automatic time setting is not currently possible. The items should be
| followed by the caption “Setting the time and date automatically with
| {carrier name} requires a data connection.”
|
| In either of the cases where automatic time setting is not currently
| possible, the “Set the time and date:” radio items should be
| insensitive if “Manually” is already chosen (so you can’t switch to
| “Automatically” until there’s a suitable connection), but sensitive
| if “Automatically” is already chosen (so you can switch to “Manually”
| if you want).
|
| When “Set the time and date:” is set to “Manually”, *or* it is set
| to “Automatically” but automatic time setting is not currently
| possible, the current datestamp item should be a navigation item that
| navigates to the “Set Time & Date” screen. When automatic time
| setting is currently in effect, the current datestamp item should be
| insensitive.

> It'd be possible to do a time-zone lookup based upon GPS location, 
> although this would be complicated...
> 
> As for automatic "time" updates, besides NITZ, the two mechanisms
> I'm aware of are GPS, and NTP, the latter being the only requiring
> a "data" connection.
> 
> Finally, I'd like my phone to just do this stuff for me
> automatically, however in the case where my phone is "offline", do
> I really need the "Time & Date" settings page to tell me?

In general I think apps should tell you when something fails because
you don't realize you're offline: opening a Web page, checking mail,
starting a multiplayer game, whatever. Normally it will be simpler for
an app to do that than it is in the time setting case, precisely
because in this case it's not necessarily a data connection that you need.

> In general my phone is offline when I tell it to be ( eg. "airplane
> mode" ), or when I'm away from home and my phone is roaming ( and
> "data while roaming" is disabled ). In these cases, I may choose
> manually override the time zone, or leave it as is ( again like
> when I'm on an airplane ).  I rarely say, "Oh my phone is offline,
> I need to do something about that...".
> 
> [a] http://en.wikipedia.org/wiki/NITZ

In the above text I've said that you can still set the time and date
manually if the setting is "Automatically" but you don't currently
have an applicable connection.

Thanks
- -- 
mpt

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