The lack of open public spectrum is a clear mistake of the governing authorities. To run a GSM+3G+LTE network for the annual CCC congress, we have to ask commercial operators for ARFCNs to use, every year all over again, and every year it is unclear what the response will be, often up to very near the build up of the event. If we had a publicly usable spectrum for 2G,3G,4G (and 5G?) here in Germany, so much more innovation and free/open infrastructure projects would happen in mobile communication. Network coverage holes are high up on the news these days, just imagine if locals were allowed to help themselves and not rely on profit-only oriented commercial operators...
Germany's new "campus network" spectrum regime is the first step towards this. It isn't true free access for everyone, but it makes approx 90 MHz of usable mobile spectrum in the ~3.5 GHz band available.
The Netherlands has had around 5 MHz of DECT guardband spectrum available for private use, which is also useful. The UK has announced a new way to "share" access to 3.3 MHz of DECT guardband (plus 10 MHz of 2.3 GHz, and any unused mobile operator spectrum).
Coverage blackspots are definitely a problem, but with these moves, maybe we can see some initiatives like these helping? The biggest challenge is likely in getting incumbent operators (paying billions for spectrum) to work with people willing to build these kinds of networks - until that happens adoption may struggle, and it is hard to onboard users and create good business models. Spectrum was definitely a barrier but in rural areas in northern Europe, hopefully this will be less of an issue going forward.
I wonder, what’s the purpose of this? GSM is going away and being replaced with IMS which is essentially SIP over a specific APN.
Does this problem also apply to data links (from my experience I’ve never had issues maintaining a data connection despite roaming between cells and even countries)? If not then I don’t see how this effort is worthwhile.
The majority of the linked document details the purpose of the system. As far as worthwhile it's pretty clear that Rhixomatica and the villages in Oaxaca think it's useful:
"The solution we are implementing is inspired by the actual social and physical structure that we aim to service: each village in Oaxaca has their own fully independent core network stack, and each community is fully in charge of their own infrastructure. There is no central authority governing across communities, by deliberate choice. Because the infrastructure is operated in remote rural areas, often from a pole on a hill crest running on solar panels, and with directional wifi over large distances, network links between villages can be unstable."
A valid response is that as soon as a data service uplink is provided, then common IP routing via the GGSN could take over, and everyone could be using messenger apps. D-GSM (btw not limited to 2G) is indeed most interesting for routing "old style" voice calls and SMS. These are still in wide use, and arguably more stable than pure data links, which have to compete for bandwidth with other data (base stations can actively prioritise voice).
If you think LTE (4G), then everything is already a data link at first sight; but most carriers still use CSFB, where the voice calls fall back to a 2G RAN.
The concept is important, as it structures the call flows in a new way, regardless of content (SMS, data, voice). The bearer (2G/3G, 4G, 5G) is much less important.
Once new architecture exists and is proven to converge at scale, then homing a subscriber data connection through one mechanism or another (GTP, PMIP, ..., wireguard?) is just a technical choice.
