Hi Lynxis,
thanks for your quick and helpful response!
I don't understand your goal. It might be possible to work without a
mobile network.
My objective is to integrate an open source voucher protocol like cashu (https://github.com/cashubtc) into the GSM stack. The mobile device would submit a different voucher every time, which the GSM base station redeems before delivering the service. This would enable anyone with GSM hardware to serve the customer without needing to identify the customer for invoicing purposes.
I don't need a base station to submit the vouchers, but I will probably need to learn about how base stations work to implement a fully functional solution that redeems the vouchers and delivers internet. Would it be possible to borrow or rent a cheap base station for this experiment?
the network doesn't see SPN or PNN. Those fields are all meant to be
used by the phone.
Perhaps it would make sense to use the `USSD-String`since the vouchers are Base64-Strings?
Look into pySim-smpp2sim.py and RFM (remote file management).
My understanding is that this script is used to update the sim via the base station. Ideally an app on the mobile device would manage the vouchers that are submitted locally. Would it make sense for the app that already manages vouchers on the mobile device to use OMAPI to send the voucher as an ADPU to a java card applet on the sim?
Best regards, Siemon
On 12/02/26 23:30, Alexander 'lynxis' Couzens wrote:
Hi Siemon,
there is a lot of development regarding OTA and SAIP atm in pysim.
My goal is to customize an eSIM profile so that it presents a generic/custom string to the base station during the connection establishment. I have a few specific questions regarding the best approach:
what do you mean by a generic/custom string to the base station?
- Profile Personalization: In personalization.py, which Elementary Files
(EF) would you recommend modifying to ensure a custom string is visible to the network side (e.g., EF.SPN, EF.PNN, or others)?
the network doesn't see SPN or PNN. Those fields are all meant to be used by the phone.
- Dynamic Content: Is it feasible to update these strings dynamically on
the eUICC without re-downloading the entire profile, for example via a Java Card applet or specific OTA commands supported by the Osmocom stack?
It is possible to use OTA/RFM to change those which could be simpler than downloading a full profile every time.
- Lab Setup: I am hoping to set up a local base station to test the
interaction with this modified eSIM.
Which hardware would you recommend for testing this? I already have a red pitaya and am considering setting up a radio front-end for it. However, Calypso phones are cheaper and I wonder if they would be sufficient for this test.
I would recommend to not go for a custom solution, take a well known working one. I would try to use a well supported SDR with a GPSDO or go for a small BTS e.g. sysmobts 1002.
I don't understand your goal. It might be possible to work without a mobile network.
Any guidance on which parts of the pySim codebase I should focus on for this "on-the-fly" customization would be greatly appreciated.
Look into pySim-smpp2sim.py and RFM (remote file management).
Regards, lynxis