Content for  TS 23.540  Word version:  19.0.0

MT SMS interaction between SC and SMS-GMSC follow the current procedure as defined in TS 23.040.

SMS-GMSC invokes the Nnrf_NFDiscovery to discover and select the UDM instance(s), supporting SMS SBI interfaces, and managing 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.

If no UDM supporting SMS SBI could be discovered, the NRF indicates so to SMS-GMSC (by not including any UDM instance in the discovery response), and SMS-GMSC shall quit the SBI-based procedure and fallback to legacy (MAP/Diameter) protocol based procedures, as defined in TS 23.040, or if a UDM supporting SMS SBI is discovered and selected, NRF returns the IP addresses or FQDNs of the serving UDM to provide Nudm_UECM_SendRoutingInfoForSM service to SMS-GMSC.

The SMS-GMSC invokes Nudm_UECM_SendRoutingInfoForSM (GPSI) to the UDM to get the serving node information for all access types for the UE.

The UDM shall check the registration/reachability flags to determine the potential target nodes, e.g. the SMSF. For MT SM transfer via the IP-SM-GW, the UDM shall invoke the Nipsmgw_SMService_RoutingInfo to provide the SMSF Instance Id to the IP-SM-GW. The address of the IP-SM-GW to be contacted by the UDM may be configured locally or may be received from the HSS via the Nudm_UECM service for IP-SM-GW registration, containing the registration data provided by the IP-SM-GW. If the MPS for Messaging indication is set (enabled) in the UDM, the UDM includes the MPS for Messaging indication in the Nipsmgw_SMService_RoutingInfo request and sets the transport priority (e.g., DSCP and the Message Priority header) of the response to a value appropriate for MPS and handles the request with priority.

The IP-SM-GW shall send the Nipsmgw_SMService_RoutingInfo response to the UDM. If the MPS for Messaging indication from the UDM is set (enabled), the IP-SM-GW includes a Message Priority header with a value appropriate for MPS. If the MPS for Messaging indication is set (enabled) from the UDM, the IP-SM-GW includes the MPS for Messaging indication in the response and sets the transport priority (e.g., DSCP and the Message Priority header) of the response to a value appropriate for MPS and handles the response with priority.

The UDM responds to the SMS-GMSC by sending the Nudm_UECM_SendRoutingInfoForSM response, including IP-SM-GW address, the indication for SMSF SMS_SBI support and the indication for IP-SM-GW SMS_SBI support. If the MPS for Messaging indication is set (enabled) in the UDM, the UDM includes the MPS for Messaging indication in the Nudm_UECM_SendRoutingInfoForSM response and sets the transport priority (e.g., DSCP and the Message Priority header) of the response to a value appropriate for MPS and handles the response with priority.

The SMS-GMSC forwards the SMS message to the IP-SM-GW, and then the IP-SM-GW performs service authorization and domain selection to determine the domain for delivery of the Short Message as defined in TS 23.204. If the SMSF is selected, the IP-SM-GW forwards the SMS message to the SMSF. If the IP-SM-GW has more than one SMSF address to use for SMS transport towards the UE, then the IP-SM-GW 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 and IP-SM-GW SBI support: If both the SMSF and the IP-SM-GW indicate support for SMS_SBI, the SMS-GMSC discovers the appropriate service instance(s) of the target IP-SM-GW and forwards the SMS message to the IP-SM-GW by invoking the Nipsmgw_SMService_MtForwardSm service operation. And then the IP-SM-GW forwards the SMS message to the SMSF by invoking the Nsmsf_SMService_MtForwardSm service operation. If the SMS message from the SC provides a priority indication (the priority indication is out of scope of the present document) or if the MPS for Messaging indication from the UDM is set (enabled), the SMS-GMSC sets the transport priority (e.g., DSCP and the Message Priority header) of the response to a value appropriate for MPS and handles the response with priority. If the SMSF or the IP-SM-GW indicates that it does not support SMS_SBI, the SMS-GMSC should forward the SMS message to the IP-SM-GW using the legacy MAP/Diameter protocol. Then the IP-SM-GW forwards the SMS message to the SMSF using the legacy MAP/Diameter protocol. If the SMS message from the SC provides a priority indication (the priority indication is out of scope of the present document) or if the MPS for Messaging indication from the UDM is set (enabled), the IP-SM-GW sets the transport priority (e.g., DSCP and Diameter priority) of the SMS message to a value appropriate for MPS and handles the response with priority. MPS for Messaging is not supported for the MAP protocol. The following steps follow the procedures for legacy MT SMS message transfer, as illustrated in Figure 15aa of TS 23.040. If the MPS for Messaging indication from the UDM is set (enabled), the IP-SM-GW includes a Message Priority header with a value appropriate for MPS when forwarding the SMS message.

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

The SMSF delivers the delivery report to the IP-SM-GW by sending the Nsmsf_SMService_MtForwardSm response to the IP-SM-GW.

The IP-SM-GW delivers the delivery report to the SMS-GMSC by sending the Nipsmgw_SMService_MtForwardSm response to the SMS-GMSC.

The IP-SM-GW may report the SM-Delivery Status to the UDM by invoking the Nudm_ReportSMDeliveryStatus_Request.

The UDM responds with the Nudm_ReportSMDeliveryStatus_Request response to the IP-SM-GW.

The SMS-GMSC may report the SM-Delivery Status to the UDM by invoking Nudm_ReportSMDeliveryStatus_Request and the UDM shall ignore the information provided in this report.

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

The MT SMS over NAS procedure between the SMSF, the AMF and the UE is the same as in step 6c to 6d of Figure 4.13.3.6-1 of TS 23.502.