Re: bluetooth DUN silently discarding "invalid" APNs

[Marc Herbert <Marc Herbert gmail com>]

>> By the way it is not possible to enter a blank APN either (asking the
>> network use the default APN). This again works perfectly with wvdial.
>> And this is valid.

> Yes, it's valid, but note that the "default" APN is stored in the
> *device*, not the SIM card, and has no relation to the SIM card at all.
> So if you ever swap SIM cards, or use a different provider, then the APN
> is surely going to be wrong and the dialing will fail.  However, I've
> been thinking of ways to enable using the "default" APN since that works
> for some phones that don't allow setting the APN at all via AT commands,
> but where dialing works fine.
> 

No, I was not referring to any default APN stored from the phone, but
to the case where the phone does not provide any APN to the network *at
all*.

Section 3.1 "Definitions" at the very beginning of 3GPP 23.401:

  Default APN: A Default APN is defined as the APN which is marked as
  default in the subscription data [...] when no APN is provided by
  the UE".

UE = User Equipment. The "subscription data" comes from the HSS in the network.

In the same spec see also paragraph 12 in section 5.3.2.1. This
paragraph has about 5-6 sentences starting with: "If the UE does [not]
provide an APN,..."

The operator I can connect to using a blank APN did not even exist yet
when I bought the phone, so for sure the phone is not sneakily
providing any "good default APN" to get me online. It is a old
2.5G EDGE phone by the way.