Content for TS 23.540 Word version: 19.0.0

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5.1 Procedure for SBI-based MT SMS 5.1.1 General 5.1.2 Successful Mobile Terminated short message transfer without SMS Router/ IP-SM-GW
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5 Procedures for SBI-based SMS p. 11

5.1 Procedure for SBI-based MT SMS p. 11

5.1.1 General p. 11

The procedure is used to support the Mobile Terminated short message transfer for SBI-based interfaces as defined in clause 4.1, which is based on Short message mobile terminated procedure defined in clause 10.1 of TS 23.040 and clauses 4.13.3.6, 4.13.3.7 and 4.13.3.8 of TS 23.502.

This new services introduced in this procedure can be registered in NRF, and discovered by NF service consumers.

SMSF/SMS Router/IP-SM-GW should indicate whether it supports SMS_SBI or not. For the case of SMSF/IP-SM-GW, "SBI support indication" should be brought when SMSF/IP-SM-GW registers in UDM. For the case of SMS Router, "SBI support indication" should be configured locally in UDM, together with the SMS Router address. UDM stores the "SBI support indication" indication and provides it to the SMS-GMSC during Routing Info retrieval. SMS-GMSC selects legacy or SBI based protocol based on the indication received during Routing Info retrieval.

5.1.2 Successful Mobile Terminated short message transfer without SMS Router/ IP-SM-GW p. 12

Reproduction of 3GPP TS 23.540, Fig. 5.1.2-1: MT SMS over NAS without SMS Router/ IP-SM-GW

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

Step 1.

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

Step 2a.

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.

Step 2b.

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.

Step 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.

Step 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. 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 as specified in TS 29.500) of the response to a value appropriate for MPS and handles the response with priority.

Step 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 the SMSF indicates that it supports SMS_SBI, the SMS-GMSC forwards the SMS message to the SMSF by invoking 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 SMS message to a value appropriate for MPS and handles the SMS message with priority.

If the SMSF indicates that it does not support SMS_SBI, the SMS-GMSC should forward 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 SMS-GMSC sets the transport priority (e.g., DSCP and Diameter priority) of the SMS message to a value appropriate for MPS and handles the SMS message with priority. MPS for Messaging is not supported for the MAP protocol. And the following steps follow the procedures for legacy MT SMS message transfer, as illustrated in Figure 15a of TS 23.040.

Step 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 TS 23.502.

Step 7.

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

Step 8.

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

Step 9.

UDM responses Nudm_SMReportStatus_Request response to SMS-GMSC.

Step 10.

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

Step 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 TS 23.502.