23.2043GPPRelease 17Stage 2Support of Short Message Service (SMS) over generic 3GPP Internet Protocol (IP) accessTS
Figure 6.4: Successful encapsulated Short Message termination procedure
1) The UE registers to the S-CSCF according to the IMS registration procedure.
2) The SMS-SC forwards the Short Message (SMS‑DELIVER) to the SMS-GMSC.
3) Steps 3a to 3c are performed if SMS GMSC interrogates the HSS with MSISDN. For MT-SMS without MSISDN as defined in clause 6.0a, step 3d is performed if an IP-SM-GW address is available and need not be retrieved, and steps 3e to 3f are performed if an IP-SM-GW address needs to be retrieved.
3a) The SMS‑GMSC interrogates the HSS (using MSISDN) to retrieve routeing information. Based on the pre-configured IP-SM-GW address for the user, the HSS forwards the request to the corresponding IP-SM-GW.
NOTE 1: The Send Routeing Info for SM request is not forwarded if it has been sent originally from the IP‑SM‑GW.
NOTE 2: If there is only a single IP‑SM‑GW address, the IP‑SM‑GW address does not need to be pre-configured in the HSS, the Send Routeing Info for SM request can be forwarded on the STP level.
3b) The HLR/HSS returns the addresses of the current MSC, SGSN, MME or SMSF to the IP‑SM‑GW for delivery of the Short Message in CS/PS domain. The HLR/HSS also returns the IMSI, for the IP‑SM‑GW to correlate the receipt of Short Message from the MT Correlation ID within the IMSI field of the Forward Short Message.
3c) The IP SM GW creates a MT Correlation ID as per TS 23.040  which associates the Send Routeing Info for SM with the subsequent Forward Short Message messages(s), and stores this along with the IMSI of the receiving subscriber. The IP-SM-GW returns only one address, which is of itself, along with the MT Correlation ID as routeing information to the SMS-GMSC.
NOTE 3: For the case where the IP‑SM‑GW address is not pre-configured in the HSS, the Send Routeing Info for SM request will be forwarded on the STP level, the IP-SM-GW returns the address of itself as routeing information to SMS-GMSC upon receipt of the forwarded Send Routeing info for SM request.
3d) Interrogation is skipped in the context of T4 device triggering if an up to date IP-SM-GW address is already available at the SMS-SC/SMS-GMSC.
3e) The SMS GMSC interrogates the HSS (using IMSI) to retrieve routeing information.
3f) HLR/HSS returns the addresses of IP-SM-GW, MSC (MME), SGSN and/or SMSF. If IMS is to be used for MT-SMS then continue with step 4.
4) If steps 3a to 3c have been taken, SMS-GMSC delivers the Short Message (SMS‑DELIVER) to IP-SM-GW (AS) including the MT Correlation ID received from the IP‑SM‑GW, in the same manner that it delivers the Short Message to an MSC, SGSN, MME or SMSF. Otherwise, SMS-GMSC delivers the Short Message (SMS DELIVER) to IP-SM-GW (AS) including the IMSI.
5) The IP‑SM‑GW performs service authorization based on the stored subscriber data described in the clause 6.1. The IP‑SM‑GW shall check whether the subscriber is authorised to use the short message service (e.g. Operator Determined Barring settings), similar to the authorization performed by MSC/SGSN/MME/SMSF in case the Short Message is delivered via CS or PS domain. In addition, the IP‑SM‑GW shall also check whether the subscriber is authorised to use the encapsulated Short Message delivery via IMS. If the result of service authorization is negative, the IP‑SM‑GW shall not forward the message, and shall return the appropriate error information to the SMS-SC in a failure report. Domain selection function is not performed for MT-SMS without MSISDN (i.e. when IMSI is received in step 4) and IMS is used for delivery. Otherwise (i.e. when a MT Correlation ID is received in step 4), the IP-SM-GW performs domain selection function to determine the preferred domain for delivering the message according to operator policy and user preferences. The logic for selecting preferred route for message delivery is a matter of implementation.
6) If the preferred domain is IMS, the IP-SM-GW (AS) uses the TEL-URI associated with the IMSI of the message received for the target UE to send the Short Message (SMS‑DELIVER, SC Address) encapsulated in the appropriate SIP method towards the S-CSCF. If TEL URI is not available, SIP URI is used.
7) S-CSCF forwards the encapsulated Short Message (SMS-DELIVER, SC Address) to the UE.
8) The UE acknowledges the SIP request.
NOTE 4: This is not yet the Delivery report.
9) The S-CSCF forwards the acknowledgement of the SIP request to the IP-SM-GW (AS).