6.5a Unsuccessful SM termination procedure

23.2043GPPRelease 17Stage 2Support of Short Message Service (SMS) over generic 3GPP Internet Protocol (IP) accessTS

When a Short Message fails to reach the UE via the selected domain, a failure delivery report is returned to the IP‑SM‑GW. The IP‑SM‑GW takes responsibility to re-attempt the delivery of the message in another domain which is listed in the sequence of the priority in the IP‑SM‑GW while the domain selection is performed during the SM termination procedure. If the message successfully reaches the UE after re-delivery, the IP‑SM‑GW forwards the received successful Delivery report to the SMS‑GMSC. Otherwise, if the message still fails after the IP‑SM‑GW has tried all selectable domains, the IP-SM-GW forwards the received unsuccessful Delivery report to the SMS‑GMSC and sends Report SM Delivery Status message to the HLR/HSS. The HLR/HSS then records the corresponding Messages Waiting Data (MWD), and an Alert service centre procedure may be initiated as described in clause 6.5b or 6.6. The IP-SM-GW sets UE-Not-Reachable-for-IP (UNRI) locally as defined in TS 23.040 [2].

The order in which domains are selected for message delivery by the IP‑SM‑GW is subject to operator policy and/or user preferences and any known or assumed timer values in the SMS-GMSC for the Forward Short Message message (see NOTE 1).

The following flow shows only an example order of selected domains, i.e. the IMS is the preferred domain, followed by the PS domain, and finally the CS domain.

NOTE 1: If the timer at the SMS-GMSC has been configured to a short value (near to the minimum value), the IP‑SM‑GW may not have sufficient time to try the message delivery in all three domains. This problem can be resolved by several implementation solutions, e.g. re-configuring the SMS-GMSC timer to be longer, enhancing the IP-SM-GW to try the delivery only in two or one domain(s).

Figure 6.5a: Unsuccessful SM termination procedure

1) As described in clause 6.4, the Short Message is routed to the UE via S‑CSCF after the domain selection is performed in the IP‑SM‑GW and all the available domains have been listed in the sequence of the priority in the IP‑SM‑GW. The message fails to reach the UE, e.g. due to the UE not being reachable in IMS, or exceeded memory capacity of the UE.

2) The S‑CSCF sends an appropriate failure message according to normal IMS procedure as defined in TS 23.228 [9], and sends it to the IP‑SM‑GW (AS) including an appropriate error value. This Delivery report is an acknowledgement to the Short Message received by the S-CSCF in step 1.

NOTE 2: When the failure message is sent from the UE, e.g. the UE notifies the network that the UE has been unable to accept a Short Message because its memory capacity has been exceeded, the S‑CSCF forwards the failure message to the IP‑SM‑GW (AS).

3) IP‑SM‑GW (AS) acknowledges the failure message to S‑CSCF.

4) The IP‑SM‑GW verifies the error cause of the failure delivery report. If the error is due to exceeded memory capacity of the UE, the IP‑SM‑GW forwards the Delivery report (SMS‑DELIVER‑REPORT) back to the SMS-GMSC and the procedure continues as described in step 16. Otherwise, the IP‑SM‑GW forwards the Short Message to the domain which is listed in the second place in its priority list. It is supposed that the SGSN is selected.

5) The SGSN delivers the message to the UE but the message fails to reach the UE, e.g. the UE is not reachable in PS domain.

NOTE 3: If the delivery succeeds in the PS domain at this point, the procedure for successful message delivery over PS domain is described in clause 6.4.

6) The SGSN generates a Delivery report (SMS‑DELIVER‑REPORT) and sends it to the IP‑SM‑GW, including an appropriate error value. This Delivery report is an acknowledgement to the Short Message received by the SGSN in step 5.

7) The IP-SM-GW forwards the Short Message to the domain which is listed in the third place in its priority list. It is supposed that the MSC is selected.

8) The MSC delivers the message to the UE but the message fails to reach the UE, e.g. the UE is not reachable in CS domain.

NOTE 4: If the delivery succeeds in the CS domain at this point, the procedure for successful message delivery over CS domain is described in clause 6.4.

9) The MSC generates a Delivery report (SMS‑DELIVER‑REPORT) and sends it to the IP‑SM‑GW, including an appropriate error value. This Delivery report is an acknowledgement to the Short Message received by the MSC in step 8.

10) The IP-SM-GW forwards the Short Message to the domain which is listed in the forth place in its priority list. It is supposed that the MME is selected.

11) The MME delivers the message to the UE but the message fails to reach the UE, e.g., the UE is not reachable in PS domain.

12) The MME generates a Delivery report (SMS-DELIVER-REPORT) and sends it to the IP-SM-GW, including an appropriate error value. This Delivery report is an acknowledgement to the Short Message received by the MME in step 11.

13) The IP-SM-GW forwards the Short Message to the domain which is listed in the fifth place in its priority list. It is supposed that the SMSF is selected.

NOTE 5: If the IP-SM-GW acquires two SMSF addresses from the HSS, the IP-SM-GW tries to deliver the message one by one.

14) The SMSF delivers the message to the UE but the message fails to reach the UE, e.g. the UE is not reachable in PS domain.

15) The SMSF generates a Delivery report (SMS-DELIVER-REPORT) and sends it to the IP-SM-GW, including an appropriate error value. This Delivery report is an acknowledgement to the Short Message received by the SMSF in step 14.

16) The IP‑SM‑GW sends a Delivery report to the SMS‑GMSC.

NOTE 6: The SMS-GMSC is aware of the availability of the UE on only one domain (see clause 6.4), and so will not attempt redelivery to another domain after receiving a failure report.

17) The IP-SM-GW sends a Report SM Delivery Status to the HSS with accurate results from different domains. The HSS records the corresponding MWD, i.e. the SMS‑SC address which stores the un-delivered message and the failure reason which indicates that the message failed to be sent by IP‑SM‑GW due to the UE not being available or the memory capacity of the UE being exceeded. The IP-SM-GW sets UNRI locally.

18) The IP-SM-GW subscribes to the HSS for a one-time notification of the UE being reachable again. The HSS records the subscription and instructs the transport layer to report when the UE is reachable.

19) The SMS-GMSC sends a Report SM Delivery Status to the HSS. The HSS shall ignore the information provided in this report.