SGsAP Interface for LTE/ePC CSFB Support
It would be great to support combined 2G+4G networks by having a SGsAP interface in our MSC/VLR.
This interface is used for circuit-switched fallback between the MME and the MSC/VLR.
It's not based on ASN.1 and also not using SIGTRAN. Rather' it's using GSM-style TLVs over plain SCTP. For a detailed specification, see 3GPP TS 29.118.
Let's use this ticket to document what it would take to add this to OsmoMSC.
For a high-level summary of how CSFB and SMS-over-SGs, see http://www.leliwa.com/downloads/CSFB_and_SMSoSGs.pdf