Fwd: [MM 0.6] Plumb up the SPN display-rule bits

[Nathan Williams <njw google com>]

[I accidentially sent this reply just to Dan; I wondered why it hadn't gotten any traction on the list. Resending]

> So let me think this through...  bit 1 is about what to display when the
> registered network is a "well-known" network, ie a PLMN known to the
> SIM.

Right.

> 0 means that the phone does not need to show the registered network name
> if it's "well-known" network.  They probably should have just said "0
> means the opposite of 1", the terminology here is kinda confusing.
>
> 1 means that the registered network name is required to be shown if the
> network is a well-known network.  I guess b1=1 would force showing a
> roaming partner's name instead of the SPN if the roaming partner is
> known to the SIM?

It's in addition to the SPN. "When registered on the HPLMN [...] The
SP Name shall be displayed" (122.101 A.4)

>
> Perhaps combining both bits into a "RequiredNameDisplay" (?) property is
> the right way to go?  We already know what PLMN we're registered with,
> and we can access the PLMN list to figure out if the registered network
> is, in fact, a well-known network or not.

> So here, when the network is not a well-known network, b2=0 means SPN
> name display is required, while b2=1 means you can display the
> registered network name.

Similarly, here, the registered network name must be displayed, and
the bit controls whether to additionally display the SPN.

> If we did combine both bits into one property, then we'd get the
> following logic:
>
> enum {
>    DISPLAY_UNRESTRICTED = 0,
>    DISPLAY_REGISTERED = 1,
>    DISPLAY_SPN = 2
> } DisplayName;
>
> display = DISPLAY_UNRESTRICTED
> if (registered network is well-known) {
>   if (b1 == 1)
>      display = DISPLAY_REGISTERED
> } else {
>   if (b2 == 0)
>      display = DISPLAY_SPN
> }
>
> And then the UI client can use that hint to figure out whether it is
> required to display the SPN or the registered name.  Thoughts?

That logic involves mixing bits read from the SIM (static) with the
registered state (dynamic). We could do that, but it would have to be
somewhere other than the SIM interface, I think. I'm happier just
exporting the bits and punting the logic upstream. Partly I think
that's the safer choice since the logic is, as you note, so confusing.

   - Nathan