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Content for  TS 23.632  Word version:  17.0.0

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5.5  SMS SupportWord‑p. 32

5.5.1  General

Potential MT-SMS target nodes in the EPS are the MME/MSC and the SGSN registered at the HSS, while in 5GS MT-SMS target nodes are the 3GPP-SMSF and the Non3GPP-SMSF registered at the UDM. For the role of SMS-Router and IP-SM-GW see TS 23.040.

5.5.2  MT-SMS Routing Information Retrieval

Figure 5.5.2-1 shows the interaction when the SMS-GMSC retrieves routing information from the HSS for MT-SMS delivery.
Reproduction of 3GPP TS 23.632, Figure 5.5.2-1: SMS Routing Info Retrieval
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Step 1.
The HSS receives a request for routing information from the SMS-GMSC via MAP or S6c.
Step 2.
The HSS queries the EPS-UDR via Ud to read the registered MME/MSC, the registered SGSN, and the UE-not-reachable flags for SMS in MME/MSC, SGSN and UDM.
Step 3.
If the UE-not-reachable flag for SMS in UDM is not set and unless the user is known not to be registered in 5GC, the HSS retrieves the registered SMSF addresses (if any) from the UDM.
Step 4-5.
The UDM retrieves the requested information from the 5GS-UDR.
Step 6.
The UDM forwards the retrieved addresses to the HSS if any.
If SMS over NAS is not allowed for the user in 5GS based on subscription data, e.g. SMS teleservice is not provisioned or SMS is barred, the UDM indicates in the response to the HSS the corresponding error condition.
Step 7.
The HSS returns the relevant MT-SMS target node addresses registered in HSS and/or UDM to the SMS-GMSC and the procedure is terminated.
Otherwise, if there is no MT-SMS target node address registered in HSS nor in UDM, a negative response (Absent Subscriber SM) is sent to the SMS-GMSC and the procedure continues with steps 8 to 11.
Step 8.
The HSS includes the SMSC address to the Message Waiting Data (MWD) stored in the EPS-UDR and informs the SMSC as defined in TS 23.040. The relevant UE-not-reachable flags are set in the EPS-UDR.
If SMS is not allowed for the user in 5GS according to subscription data as indicated in step 6, steps 9 to 11 are not executed so that the HSS does not subscribe to notifications about reachability for SMS in the UDM, and the procedure is terminated.
Step 9.
The HSS subscribes in UDM to be notified when the UE becomes reachable for SMS (i.e. when the UE gets in radio contact with the AMF while an SMSF actually is registered, or when an SMSF gets registered) by using the Nudm_EE_Subscribe service operation (SUPI, UE Reachability for SMS event) as defined in TS 23.502.
Step 10.
The UDM stores the EE-subscription (Reachability for SMS) in the 5G-UDR.
Step 11.
The UDM acknowledges the subscription to the HSS.
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5.5.3  MT-SMS Delivery FailureWord‑p. 33

Figure 5.5.3-1 shows the interaction when the SMS-GMSC sends Report-SM-Delivery-Status to the HSS.
Reproduction of 3GPP TS 23.632, Figure 5.5.3-1: MT-SMS Delivery Failure
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Step 1.
The HSS receives a Report-SM-Delivery-Status from the SMS-GMSC indicating the MT-SMS target nodes at which MT-SMS delivery was unsuccessful.
Step 2-3.
The HSS reads and updates the Message Waiting Data stored in the EPS-UDR.
Step 4.
The HSS acknowledges the receipt of the delivery status to the SMS-GMSC.
Step 5.
If during step 3 the UE-not-reachable flag for UDM was modified from false to true, the HSS subscribes to notification on UE-Reachability for SMS at the UDM, using the Nudm_EE_Subscribe service operation as defined in TS 23.502.
Step 6-7.
The UDM checks that the UE is registered in an AMF and SMSF. The UDM then queries the 5GS-UDR to see whether the UE-Reachability event has already been subscribed at the registered AMF(s) (i.e. whether URRP-AMF flag is set).
Step 8-9.
If not already subscribed, the UDM subscribes to UE-Reachability notification at the AMF(s) using the Namf_EE service.
Step 10-11.
The UDM stores the received EE-Subscription in the 5GS-UDR and if steps 8-9 were performed, the UDM sets the relevant URRP-AMF flags in the 5GS-UDR.
Step 12.
The UDM acknowledges the subscription to the HSS.
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5.5.4  SMS AlertingWord‑p. 35

Figure 5.5.4-1 shows the interaction when the UE becomes available.
Reproduction of 3GPP TS 23.632, Figure 5.5.4-1: SMS Alerting
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Step 1.
The UDM receives a Notification from the AMF or an SMSF Registration.
Step 2-3.
The UDM queries the 5GS-UDR to see whether any NF (e.g. the HSS) has subscribed to notifications on UE-reachability for SMS events.
Step 4.
The UDM acknowledges the message received in step 1.
Step 5.
If the HSS has subscribed to UE reachability for SMS notification,
the UDM notifies the HSS as described in TS 23.502.
Step 6-7.
The UDM updates (clears) the relevant reachability flag. and if the HSS has been notified in step 5 also deletes the (one-time) EE-subscriptions of UE reachability for SMS in the 5GS-UDR.
Steps 8 to 11 are skipped if the HSS has not been notified in step 5.
Step 8.
The HSS reads Message Waiting Data from the EPS-UDR.
Step 9-10.
The HSS sends Alert-SC to all SMS-GMSCs stored in the MWD.
Step 11.
The HSS removes the SMS-GMSCs from the MWD stored in the EPS-UDR and clears the relevant UE-not-reachable flags from the EPS-UDR.
Step 12.
The HSS acknowledges receipt of the Notification to the UDM.
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5.5.5  MT-SMS Routing Information Retrieval Over NudrWord‑p. 37

Figure 5.5.5-1 shows the interaction when the SMS-GMSC retrieves routing information from the HSS for MT-SMS delivery when the HSS uses the Nudr SBI.
Reproduction of 3GPP TS 23.632, Figure 5.5.5-1: SMS Routing Info Retrieval over Nudr
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Step 1.
The HSS receives a request for routing information from the SMS-GMSC via MAP or S6c.
Step 2.
The HSS queries the EPS-UDR via Ud to read the registered MME/MSC, the registered SGSN and the UE-not-reachable flags for MME/MSC, SGSN, 3GppSMSF and Non3GppSMSF.
Step 3-4.
If the UE-not-reachable flags for 3GppSMSF and Non3GppSMSF are not set and unless the user is known not to be registered in 5GC, the HSS retrieves the registered SMSF addresses (if any) from the 5GS-UDR.
Step 5.
The HSS returns the relevant MT-SMS target node addresses registered in HSS and/or UDM to the SMS-GMSC and the procedure is terminated.
Otherwise, if there is no MT-SMS target node address registered in HSS nor in UDM, a negative response (Absent Subscriber SM) is sent to the SMS-GMSC and the procedure continues with steps 8 to 11 in figure 5.5.2-1.
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5.5.6  Support for SMS over IP

5.5.6.1  General

In deployment scenarios where 2G/3G/4G accesses are available, SMS over IP is supported as described in TS 23.204, and the interactions between HSS and UDM are those defined in clauses 5.5.2, 5.5.3 and 5.5.4.
For MT-SMS delivery over 5G NAS in deployment scenarios where support for SMS over IP is also required but 2G/3G/4G accesses are not supported, the MAP-C and/or Diameter S6c refence points with the SMS-GMSC and the MAP-J and/or Diameter S6c reference points with the IP-SM-GW are exposed by the UDM. The UDM and the HSS (IMS) need to interact for the registration of the IP-SM-GW address as defined in clause 5.5.6.2. Clauses 5.5.6.3 and 5.5.6.4 define the interworking between the UDM and the HSS (IMS) during delivery failure and alert procedures.
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5.5.6.2  IP-SM-GW registration and SMS routing information retrieval in 5GC only deployments

Figure 5.5.6.2-1 shows the interaction for the registration of the IP-SM-GW address in the UDM and subsequent SMS routing information retrieval.
Reproduction of 3GPP TS 23.632, Figure 5.5.6.2-1: IP-SM-GW registration in UDM and SMS routing info retrieval in 5GC only deployments
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Step 1.
The IP-SM-GW registers its address in HSS (IMS) via Sh as defined in TS 23.204. If the EPS-UDR is used, the HSS (IMS) stores the IP-SM-GW address in the EPS-UDR.
Step 2.
The HSS forwards the IP-SM-GW registration to the UDM using a Nudm_UECM_IPSMGWRegistration request. The request includes the address of the IP-SM-GW to be registered in the UDM. If the 5GS-UDR is used, the UDM stores the IP-SM-GW address in the 5GS-UDR.
Step 3.
The UDM confirms the IP-SM-GW registration with a successful Nudm_UECM_IPSMGWRegistration response. After successful registration of the IP-SM-GW address, the UDM checks whether message waiting data are stored and alerts all SCs using procedures described in TS 23.204.
Step 4.
The UDM receives a request for routing information from the SMS-GMSC via MAP or Diameter. If the 5GS-UDR is used, the UDM queries the 5GS-UDR to read the registered SMSF and/or IP-SM-GW, if any. Routing information is provided to SMS-GMSC from IP-SM-GW or UDM.
The options shown are based on the options for MT SMS procedure described in clause 6.4 of TS 23.204, considering a 5GC only deployment where UDM is present and HLR/HSS serving 2G/3G/4G accesses is not deployed. Steps 4a-4c correspond to 3a-3c; step 4d corresponds to 3d; and steps 4e-4f correspond to 3e-3f, respectively, as shown in Figure 6.4 of TS 23.204.
Figure 5.5.6.2-2 shows the interaction for the deregistration of the IP-SM-GW address in the UDM.
Reproduction of 3GPP TS 23.632, Figure 5.5.6.2-2: IP-SM-GW deregistration in UDM and SMS routing info retrieval in 5GC only deployments
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Step 1.
The IP-SM-GW deregisters its address in HSS (IMS) via Sh as defined in TS 23.204. If the EPS-UDR is used, the HSS (IMS) removes the IP-SM-GW address from the EPS-UDR.
Step 2.
The HSS forwards the IP-SM-GW deregistration request to the UDM using a Nudm_UECM_IPSMGWDeregistration request. If the 5GS-UDR is used, the UDM removes the IP-SM-GW address from the 5GS-UDR.
Step 3.
The UDM confirms the IP-SM-GW deregistration with a successful Nudm_UECM_IPSMGWDeregistration response.
Step 4 - 5.
If the UDM receives a request for routing information from the SMS-GMSC via MAP or Diameter, the UDM checks if there is an IP-SM-GW address registered for the UE. If the 5GS-UDR is used, the UDM queries the 5GS-UDR to read the registered SMSF and/or IP-SM-GW, if any. If an IP-SM-GW address is not present, the UDM follows the MT SMS procedures defined in clause 4.13.3 of TS 23.502 and TS 23.040.
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5.5.6.3  MT SMS delivery failure in 5GC only deploymentsWord‑p. 39

Figure 5.5.6.3-1 shows the interactions for the unsuccessful MT SMS delivery case in a 5GC only deployment requiring SMSoIP.
Reproduction of 3GPP TS 23.632, Figure 5.5.6.3-1: MT SMS delivery failure in 5GC only deployments supporting SMSoIP
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Step 1 - 7.
The message delivery fails after the IP SM GW has tried all selectable domains, and the IP-SM-GW forwards the received unsuccessful Delivery report to the SMS GMSC, as described in steps 1-16 in clause 6.5a of TS 23.204.
Step 8.
The IP-SM-GW sends a Report SM Delivery Status message to the UDM with accurate results from different domains. If the 5GS-UDR is used, the UDM records the corresponding MWD in the 5GS-UDR.
Step 9.
The IP-SM-GW subscribes to the HSS (IMS) for a one-time notification of the UE being reachable again.
Step 10.
The HSS (IMS) records the subscription and subscribes to notification on UE Reachability for SMS over IP event at the UDM, using the Nudm_EE_Subscribe service operation.
Step 11 - 12.
The UDM checks whether UE Reachability has already been subscribed at the registered AMF(s) (i.e. whether URRP-AMF flag is set), querying 5GS-UDR if applicable. If not already subscribed, the UDM subscribes to UE Reachability notification at the AMF(s) using the Namf_EE service.
If 5GS-UDR is used, the UDM stores the received EE-Subscription from HSS (IMS) in the 5GS-UDR, and if subscription to AMF is performed in this step, the UDM sets the relevant URRP-AMF flag in the 5GS-UDR.
Step 13.
The UDM acknowledges the subscription of the HSS (IMS).
Step 14.
The SMS-GMSC sends a Report SM Delivery Status message to the UDM. The UDM shall ignore the information provided in this report.
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5.5.6.4  Alert Service Centre in 5GC only deploymentsWord‑p. 40

Figure 5.5.6.4-1 shows the interactions when the UE becomes available in a 5GC only deployment requiring SMSoIP.
Reproduction of 3GPP TS 23.632, Figure 5.5.6.4-1: Alert Service Centre procedure in 5GC only deployments supporting SMSoIP
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The steps described below are based on the procedure described in clause 6.5b of TS 23.204, considering a 5GC only deployment.
Step 1.
MT SMS procedure is unsuccessful as described in clause 5.5.6.3.
Step 2.
At any time after the unsuccessful SM termination procedure, the UE may become available due to registration in IMS (step 2a). After the IMS registration is finished, the procedure continues as described in step 3.
At any time after the unsuccessful SM termination procedure, the UDM can receive a notification from AMF indicating that the UE is reachable again or an AMF registration (step 2b). The UDM checks whether any NF (e.g. the HSS) has subscribed to notification on UE Reachability for SMS over IP events, querying 5GS-UDR if applicable. If the HSS has subscribed to such notification, the UDM notifies the HSS (step 2c). As the IP-SM-GW has subscribed to the event of UE being reachable again as described in clause 5.5.6.3, the HSS shall notify the IP-SM-GW (step 2d). If the UE is already registered in IMS, the IP-SM-GW shall then send a Ready for SM message to the UDM (step 2e) and the procedure continues as described in step 3. Otherwise, the IP-SM-GW discards the notification message.
Step 3.
The UDM checks the user's MWD. If MWD is not null, the UDM sends an Alert Service Centre message to the SMS IWMSC.
Step 4.
The SMS IWMSC forwards the Alert Service Centre procedure to the SMS SC.
Step 5.
Upon receipt of the Alert Service Centre message, the SMS SC re-attempts to send the stored Short Message.
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