Section: 4.13.3.6 MT SMS over NAS in CM-IDLE state and RRC_INACTIVE with CN based MT communication state via 3GPP access
Content: Figure 4.13.3.6-1: MT SMS over NAS in CM-IDLE and RRC_INACTIVE state via 3GPP access 1-3 MT SMS interaction between SC/SMS-GMSC/UDM follow the procedure as defined in TS 23.040[ Technical realization of the Short Message Service (SMS) ]  [7] or TS 23.540[ 5G System: Technical realization of Service Based Short Message Service; Stage 2 ]  [84]. If there are two AMFs serving the UE, one is for 3GPP access and another is for non-3GPP access, there are two SMSF addresses stored in UDM/UDR. The UDM shall return both SMSF addresses. 4. The SMSF checks the SMS management subscription data. If SMS delivery is allowed, SMSF invokes Namf_MT_EnableUEReachability service operation to AMF. AMF pages the UE using the procedure defined in clause 4.2.3.3. The UE responds to the page with Service Request procedure. If the AMF indicates SMSF that UE is not reachable (including the cases that UE applies power saving enhancement as described in clause 5.31.7 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]), the procedure of the unsuccessful Mobile terminating SMS delivery described in clause 4.13.3.9 is performed and the following steps are skipped. In the case of power saving enhancement, the AMF further stores the information received in the Namf_MT_EnableUEReachability request and pages the UE when UE is considered reachable. If the UE access to the AMF via both 3GPP access and non-3GPP access, the AMF determines the Access Type to transfer the MT-SMS based on operator local policy. 5a-5b. SMSF forward the SMS message to be sent as defined in TS 23.040[ Technical realization of the Short Message Service (SMS) ]  [7] (i.e. the SMS message consists of CP-DATA/RP-DATA/TPDU/SMS-DELIVER parts) to AMF by invoking Namf_Communication_N1N2MessageTransfer service operation. The AMF transfers the SMS message to the UE. 5c-5d. The UE acknowledges receipt of the SMS message to the SMSF. For uplink unitdata message toward the SMSF, the AMF invokes Nsmsf_SMService_UplinkSMS service operation to forward the message to SMSF. In order to permit the SMSF to create an accurate charging record, the AMF also includes IMEISV, the current UE Location Information (ULI) of the UE as defined in clause 5.6.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] and if the SMS is delivered to the UE via 3GPP access, the local time zone. 6a-6b. The UE returns a delivery report as defined in TS 23.040[ Technical realization of the Short Message Service (SMS) ]  [7]. The delivery report is encapsulated in an NAS message and sent to the AMF which is forwarded to SMSF by invoking Nsmsf_SMService_UplinkSMS service operation. 6c-6d. The SMSF acknowledges receipt of the delivery report to the UE. The SMSF uses Namf_Communication_N1N2MessageTransfer service operation to send SMS CP ack message to the AMF. The AMF encapsulates the SMS message via a NAS message to the UE. If SMSF has more than one SMS to send, the SMSF and the AMF forwards subsequent SMS /SMS ack/ delivery report the same way as described in step 4-6c. If the SMSF knows the SMS CP ack is the last message to be transferred for UE, the SMSF shall include a last message indication in the Namf_Communication_N1N2MessageTransfer service operation so that the AMF knows no more SMS data is to be forwarded to UE. NOTE: The behaviour of AMF based on the "last message indication" is implementation specific. 7. In parallel to steps 6c and 6d, the SMSF delivers the delivery report to SC as defined in TS 23.040[ Technical realization of the Short Message Service (SMS) ]  [7] or TS 23.540[ 5G System: Technical realization of Service Based Short Message Service; Stage 2 ]  [84].