5.1.3 Successful Mobile Terminated short message transfer via SMS Router

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

Figure 5.1.3-1: MT SMS over NAS via SMS Router

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 serving node information for all access types for the UE.

4. The UDM shall check the registration/reachability flags to determine the potential target nodes, e.g. SMSF. For MT SM transfer via SMS Router, the UDM shall invoke the Nrouter_SMService_RoutingInfo to provide the SMSF Instance Id to the SMS Router. The address of the SMS Router to be contacted by the UDM may be configured locally.

5. The SMS Router shall send Nrouter_SMService_RoutingInfo response to the UDM.

6. UDM responds to the SMS-GMSC by sending Nudm_UECM_SendRoutingInfoForSM response, including SMS Router address, the indication for SMSF SMS_SBI support and the indication for SMS Router SMS_SBI support.

7-8. The SMS-GMSC forwards the SMS message to the SMS Router, and then SMS Router forwards the SMS message to the SMSF. If the SMS Router has more than one SMSF address to use for SMS transport towards the UE, then the SMS Router chooses which SMSF address to use first, based on operator local policy.

The SMS-GMSC selects protocol based on the indications for SMSF SMS_SBI support and SMS Router SMS_SBI support.

If both SMSF and SMS Router indicate support for SMS_SBI, SMS-GMSC forwards the SMS message to the SMS Router by invoking Nrouter_SMService_MtForwardSm service operation. And then the SMS Router forwards the SMS message to the SMSF by invoking Nsmsf_SMService_MtForwardSm service operation.

If SMSF or SMS Router indicates that it does not support SMS_SBI, SMS-GMSC should forward SMS message to SMS Router by legacy MAP/Diameter protocol. Then SMS Router forwards the SMS message to the SMSF by legacy MAP/Diameter protocol. The following steps follow the procedures for legacy MT SMS message transfer, as illustrated in Figure 15aa of TS23.040.

9. 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 in 3GPP TS 23.502 [4].

10. The SMSF delivers the delivery report to SMS Router by sending the Nsmsf_SMService_MtForwardSm response to the SMS Router.

11. The SMS Router delivers the delivery report to SMS-GMSC by sending the Nrouter_SMService_MtForwardSm response to the SMS-GMSC.

12-13. The SMS-GMSC may report the SM-Delivery Status to the UDM by invoking Nudm_ReportSMDeliveryStatus_Request and UDM responses Nudm_ReportSMDeliveryStatus_Request response to SMS-GMSC.

14. The SMS-GMSC delivers the delivery report to SC as defined in 3GPP TS 23.040 [2].

15. 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 in 3GPP TS 23.502 [4].