SMS in MME is an architecture option primarily intended for networks that do not deploy GERAN or UTRAN. SMS in MME delivers SMS services over EPS NAS signalling for UE's requiring SMS services. SMS in MME architecture option enables support of SMS in the EPS via E-UTRAN without requiring deployment of 3GPP MSCs. For SMS in MME the SMS service control is performed by the MME. The MME receives SMS subscriber data and the MME verifies whether the subscriber is permitted to obtain SMS services. The SMS subscriber data received and used by the MME may be PS subscriber data (the MME directly obtains from HSS) or CS subscriber data (the MME obtains via an interworking function as described in clause C.5).

As outlined in the architecture Figure below SMS in MME requires support of SMS functionality in the MME and the MME also needs to receive SMS subscription information from the HSS. The SMS subscription information may be received through the S6a interface.

There is no impact on the UE and E-UTRAN. The SMS entities (including SMS router, etc.) functionality to support SMS in MME is the same as defined for reference point 2 and 3 in TS 23.040 except the SGd and S6c interfaces use Diameter protocols as specified in TS 29.338. The interaction between SMS in MME and SMS over IP is described in TS 23.204.

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.

The MME or the HSS may not be able to deliver the SM to the UE. This can for example happen when the UE is not attached to EPS, when the UE's SMS memory capacity is exceeded, or when the Mobile-terminated SMS is barred. When the MME cannot deliver the SM to the UE, the MME shall return a failure report to the SMS GMSC/SMS router. The SMS-GMSC/SMS router/HSS procedures for handling the failure report are specified in TS 23.040. Additionally, if the SM failed due to the UE not being reachable, the MME shall set the Mobile-Not-Reachable-Flag-in-MME-for-SMS (MNRF-MME) indication in the MME. If the UE is using extended idle mode DRX with a DRX cycle value or if the UE is in PSM (as defined in TS 23.682) that can cause mobile terminating SMS retransmissions, the MME may return a failure report to the SMS GMSC/SMS router while still paging the UE. The MME shall set the Mobile-Not-Reachable-Flag-in-MME-for-SMS (MNRF-MME) indication in the MME. If the UE subsequently becomes reachable and MNRF-MME indication is set, the MME shall send a Ready for SM (IMSI, UE-Present) message to the HSS and the MME shall clear the corresponding MNRF-MME indication for that UE. If the UE subsequently notifies the MME that SMS memory is available, the MME shall send a Ready for SM (IMSI, UE-Memory-Available) message to the HSS. Reception of a Ready for SM message or an Update Location Request message by the HSS when MNRF is set, shall trigger the SMS alert procedure as defined in TS 23.040.