I have run AMPS (1G) in my lab. I’ve run 2G (GSM) networks in production.

There’s a few dozen production LTE/5G networks out there I’ve put my stamp on, but…

Never, have I ever, run UMTS.

And that feels like a blind spot.

Sure, core wise 3G it reuses the 2G core (MSC / SGSN and friends). As a company, Omnitouch supports 2G, 4G & 5G networks – But we’ve never had the need to deploy 3G.

There’s a common theory that the odd-numbered “Gs” are shit. 3G/UMTS was crap, and 5G / NR standalone is kinda shit. There’s some merit to this theory.

3G/UMTS was a transitional tech, when it was worked on at the turn of the century, there was a growing recognition that this whole internet thing was going to be a big deal, but without the benefit of knowing exactly how people would use it.

In 2G, operators would configure on their networks how many “timeslots” were for voice calls and how many were for data. Imagine drawing a pie chart and rationing out this percentage for the internets, and that percentage for voice calls, and that’s pretty much how it went. The major difference (without going into the “CDMA” code thing) that 3G brought was that operators no longer had to decide the split of cat videos vs calls the network could decide the split.

Australia shut down GSM about a decade ago, and turned off UMTS close to two years ago, but many counties, including large parts of Europe, plan to operate 2G layers ’till the 2030s. While UMTS/3G survived ~20 years, GSM will be in it’s 40s at the point where it’s shut off in many countries.

As what my partner somewhat lovingly refers to as a “school holiday project” (Pointless thing I do rather than relaxing like a normal person) I set about trying to build an RNC – A “Radio Network Controller” the UMTS equivalent of a Base Station Controller in GSM, that I could connect to OmniMSC.

So I fired up the Airscale, configured an Iub link and looked at what it sent.

And the answer was a big fat nothing – the first rule of fight club is that the RNC initiates the connection.

I limped the project along to the stage where I had the cell reporting “Up” and visible, but to actually attach phones started to get into the CDMA part of allocating codes, and real life started to catch up with me.

Perhaps someday I’ll continue the work, but the sad truth is there’s almost no scenarios today where you wouldn’t be better to deploy LTE and a GSM layer if you need to support legacy devices – the smallest UMTS carrier is 5Mhz, and while you can’t do 1:1 frequency reuse in GSM, you’ve got 20x unique GSM TRXes in that same 5Mhz you can use.

So for now, I’m giving up, knowing slightly more about RNC architecture, but still having never done a UMTS attach.