Section: 4.13.3.3 MO SMS over NAS in CM-IDLE (baseline)
Content: Figure 4.13.3.3-1: MO SMS over NAS 1. The UE performs domain selection for UE originating SMS as defined in clause 5.16.3.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] if SMS delivery via non 3GPP access is allowed and possible. If an UE under CM-IDLE state is going to send uplink SMS message, then UE and network perform the UE Triggered Service Request procedure firstly as defined in clause 4.2.3.2 to establish a NAS signalling connection to AMF. 2a. The UE builds 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-SUBMIT parts). The SMS message is encapsulated in an NAS message with an indication indicating that the NAS message is for SMS transporting. The UE send the NAS message to the AMF. 2b. The AMF forwards the SMS message and SUPI to the SMSF serving the UE over N20 message by invoking Nsmsf_SMService_UplinkSMS service operation. In order to permit the SMSF to create an accurate charging record, the AMF adds the 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 UE has sent the SMS via 3GPP access, the local time zone. 2c. The SMSF invokes Namf_Communication_N1N2MessageTransfer service operation to forward SMS ack message to AMF. 2d. The AMF forwards the SMS ack message from the SMSF to the UE using downlink unit data message. 3-5. The SMSF checks the SMS management subscription data. If SMS delivery is allowed, the procedure 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] applies. 6a-6b. The SMSF forwards the submit report to AMF by invoking Namf_Communication_N1N2MessageTransfer service operation which is forwarded to UE via Downlink NAS transport. If the SMSF knows the submit report 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. If the UE has more than one SMS message to send, the AMF and SMSF forwards SMS /SMS ack/submit report the same way as described in step 2a-6b. 6c-6d. When no more SMS is to be sent, UE returns a CP-ack as defined in TS 23.040[ Technical realization of the Short Message Service (SMS) ]  [7] to SMSF. The AMF forwards the SMS ack message by invoking Nsmsf_SMService_UplinkSMS service operation to SMSF.