5.1.2 Successful Mobile Terminated short message transfer without SMS Router/ IP-SM-GW

23.5403GPP5G System: Technical realization of Service Based Short Message ServiceRelease 17Stage 2TS

Figure 5.1.2-1: MT SMS over NAS without SMS Router/ IP-SM-GW

1. MT SMS interaction between SC and SMS-GMSC follow the current procedure as defined in 3GPP TS 23.040 [2].

2a-2b. The SMS-GMSC should query the NRF to find the UDM instance(s), supporting SMS SBI interfaces, and managing that manages the user subscriptions of the GPSI. The SMS-GMSC may need to retrieve the PLMN ID of the recipients GPSI before the discovery of the UDM instance based on the GPSI-to-Subscription-Network resolution procedure defined in clause 5.1.7.

3. SMS-GMSC invokes Nudm_UECM_SendRoutingInfoForSM (GPSI) to the UDM to get the routing information of the nodes available for MT SMS delivery, in this case the registered serving SMSF instances for all access types for the UE.

4. The UDM shall check the registration/reachability flags to determine the potential target nodes and responds to the SMS-GMSC by sending Nudm_UECM_SendRoutingInfoForSM response, in this procedure the SMSF instance Id and the indication for SMSF SMS_SBI support are included in the response message. The UDM shall include the SMSF for 3GPP access and the SMSF for non-3GPP access separately, if both the SMSFs are currently known to be valid for the UE.

5. The SMS-GMSC forwards the SMS message to the SMSF. If the SMS-GMSC has more than one SMSF address to use for SMS transport towards the UE, then the SMS-GMSC chooses which SMSF address to use first, based on operator local policy.

The SMS-GMSC selects protocol based on the indication for SMSF SMS_SBI support.

If SMSF indicates it supports SMS_SBI, SMS-GMSC forwards the SMS message to the SMSF by invoking Nsmsf_SMService_MtForwardSm service operation.

If SMSF indicates that it does not support SMS_SBI, SMS-GMSC should forward SMS message to SMSF by legacy MAP/Diameter protocol. And the following steps follow the procedures for legacy MT SMS message transfer, as illustrated in Figure 15a of TS23.040 [2].

6. MT SMS over NAS procedure between SMSF, AMF and UE is same as the definition in step 4a to 6b of Figure 4.13.3.6-1 of 3GPP TS 23.502 [4].

7. The SMSF delivers the delivery report to SMS-GMSC by sending the Nsmsf_SMService_MtForwardSm response to the SMS-GMSC.

8. The SMS-GMSC updates the SM-Delivery Report Status to UDM by invoking Nudm_SMReportStatus_Request.

9. UDM responses Nudm_SMReportStatus_Request response to SMS-GMSC.

10. The SMS-GMSC delivers the delivery report to SC as defined in TS 23.040 [2].

11. MT SMS over NAS procedure between SMSF, AMF and UE is same as the definition in step 6c to 6d of Figure 4.13.3.6-1 of 3GPP TS 23.502 [4].