Why do we need to set the APN manually for certain providers?

[Manuel Wagesreither]

Hi all,

My company produces a device with the Sierra EM7565 Modem and we have encountered problems related to the APN setting. (A collegue of mine sent a message into this list a week ago and has received kind help by Aleksander Morgado whom I'd like to thank.)

We observed the following:

* When using a German Vodafone SIM card in Germany, 3GPP registration remains at `idle`.
* When using a German O2 SIM card in Germany, 3GPP registration advances to `home` instantly. 
* With the Vodafone SIM card, only after running `qmicli -d /dev/cdc-wdm0 -p --wds-modify-profile="3gpp,1,apn=web.vodafone.de,username=,password="`, ModemManager can connect and registration advances to `home`.
* In contrast to that, when using the Vodafone SIM card in one of our private smartphones, no manual APN setting was necessary.

I'm trying to understand why our device ran into the issues described while 3rd party smartphones do not.

I searched the internet for a bit and learned that Google is maintaining a list linking the network carriers with APNs. Is this the correct way to go? Does everyone producing GSM enabled devices (that is, us too) need to equip their devices with that list as a lookup table? Does that list work with Roaming, too? I guess an alternative would be to prompt the user for the APN, like in the old times. But still, if APNs need to be set explicitely then I don't understand why it worked with O2 instantly.


Kind Regards and thanks in advance,
Manuel