_glossary

CS	Circuit Switched
PS	Packet Switched
IMS	IP Multimedia Subsystem
VoLTE	Voice over LTE
SMS over NAS	SMS over the Non-Access Stratum Procedures
SGs	an optional interface between a 2G (GERAN) / 3G (UTRAN) MSC and an LTE/EPC MME
SGd	an optional interface enables the transfer of short messages between the MME and the SMSC using Diameter protocol
RAT	Radio Access Technology - for example GSM, UMTS, LTE or 5G-NR etc (Cellular) or Bluetooth, WiFi etc (Non-Cellular)