C.6 Unsuccessful Mobile-Terminated SMS Transfer

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

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 [14]. 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 [48]) 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.

NOTE: In the case that MME receives an indication from S‑GW that the UE has handover to non-3GPP coverage, it will not trigger this activity notification.

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 [14].