C.5 Roaming considerations

23.2723GPPCircuit Switched (CS) fallback in Evolved Packet System (EPS)Release 17Stage 2TS

The SMS in MME architecture is an optional architecture enhancement for operators that wish to avoid to the use of MSC and SGs and do not provide Fallback to 3GPP CS services over GERAN or UTRAN.

To support inbound roamers from networks that do not support the provision of SMS subscription information over S6a there are different options to provide interworking, e.g.:

– SMS over SGs.

– Use of an interworking function to convert between the S6a with SMS subscription data and S6a without SMS subscription data and D for SMS subscription. When the MME sends Ready for SM message to HSS for UE reachability notification, the interworking function also needs to convert the Ready for SM message transferred via the S6a interface to Ready for SM message transferred via the D interface.

Operators that do not deploy the SMS in MME architecture option are not required to support the S6a enhancements in the HSS or the MME.