Hi Neels,
welcome to OpenBSC code :)
Osmocom Authentication Protocol (OAP)
I would argue it makes sense to at least specify/define the protocol also to support UMTS AKA, not just plain-old GSM authentication.
This is important * for future compatibility once the SGSN suppots 3G * to use UMTS AKA for increased security over GERAN (GPRS/EDGE RAN)
Regards, Harald