Phones jumping ship from commercial networks to test network

[Das Signal]

On Mon, Jan 23, 2023 at 05:33:00PM -0800, Mychaela Falconia wrote:

> Hello GSM community,
> 
> I have a question for those who operate their own GSM networks (be it
> for fun or for research or for any other purpose) in places that DO
> have regular commercial cell service, i.e., NOT ship-at-sea, middle of
> desert or Rhizomatica-type environments: how do you deal with, and
> ideally prevent, the highly undesirable situation of other people's
> phones, not related to your operation, "jumping ship" from being
> registered to their regular commercial network to trying to register
> to your test network instead?

Hi Mychaela,

An idea could be to use this recent feature from osmo-hlr:
https://github.com/osmocom/osmo-hlr/commit/268a33e58b9de3a2a6d42f27b1b9542ffd42f584

Currently, your wife's phone probably gets an "IMSI unknown in HLR"
reject and I suppose the modem bugs after that, requiring a reboot.
With the above commit, you could try the reject cause "PLMN not allowed"
which would lead the PLMN being written on the forbidden PLMN list (EF FPLMN)
and so in the future the phone should not even try to connect (and
other phones as well). Alternatively I suppose you could update EF FPLMN
manually, that should work as well.

--DS