6.7 Service-level Interworking: IM or CPM capable UE sends an Instant Message to an SMS user

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

Figure 6.7: Successful IM origination to SMS procedure

1) The UE registers to S-CSCF according the IMS registration procedure.

2) UE submits the Instant Message to the S-CSCF using an appropriate SIP method. The UE may request to hide its Public User Identity from the recipient within the Instant Message, as described in OMA‑TS‑SIMPLE_IM‑V1_0 [12] or in OMA-TS-CPM_Conv_Fnct-V1_0 [17].

3) S-CSCF forwards the Instant Message to IP-SM-GW based on stored iFC.

NOTE 1: Subscribers with no subscription for service level interworking will not be provided with the relevant iFCs.

4) The IP-SM-GW shall decide whether to perform service-level interworking depending on SIP request header (e.g. Request-URI), operator policy, when the Instant Message is not routable in the IMS. If an ISF is deployed in the network, the ISF may take the decision to interwork using SMS and sends the message to the IP-SM-GW to perform the interworking. If IP-SM-GW decided to perform service-level interworking, the IP-SM-GW performs service authorization based on the stored subscriber data retrieved from the HLR/HSS at the time of the registration procedure as specified in clause 6.1. The IP-SM-GW shall check whether the originating subscriber is authorised to use the interworking service. 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 UE in a failure report. Otherwise, the IP-SM-GW shall use the SC Address in the subscriber data retrieved from the HSS at registration or provisioned by configuration and translates the Instant Message to a Short Message (SMS- SUBMIT) carrying SC Address, then forwards it towards SMS-SC (SC Address) via the SMS-IWMSC (as described in TS 23.040 [2]). If the size of the content of the Instant Message is larger than the size of the content that one Short Message could transfer, the IP-SM-GW shall split the content of the Instant Message into several parts, translate them to concatenated Short Messages, and forward the concatenated Short Messages to the SMS-SC as described in TS 23.040 [2]. If the sender of the Instant Message requests to hide its Public User Identity from the recipient and operator policy allows for this, the IP-SM-GW shall anonymize the identity of the user to the recipient. Otherwise, if operator policy prohibits this, the IP SM GW shall return an appropriate error to the user.

5) If service authorization is successful, the IP-SM-GW acknowledges the Instant Message.

6) Instant Message acknowledgement is forwarded by S-CSCF to UE.

NOTE 2: Steps 5 and 6 can occur anytime after the subscriber authorization check has been performed by the IP‑SM‑GW.

7) The SMS-IWMSC forwards the Short Message (SMS- SUBMIT) to the SMS-SC (see TS 23.040 [2]).

8) The SMS-SC sends a Submit report (SMS-SUBMIT REPORT) to the SMS-IWMSC (see TS 23.040 [2]).

9) SMS-IWMSC sends a Submit report to IP-SM-GW (see TS 23.040 [2]).

NOTE 3: The procedure can end in step 9. Steps 10 to 13 occur only if the IM user requested a processing notification in the Instant Message sent in step 2, as described in IETF IMDN RFC 5438 [13].

10) IP-SM-GW translates the received Submit report to an appropriate Instant Message, and forwards it to the S‑CSCF. If the IP‑SM‑GW sent concatenated Short Messages to SMS-SC in step 4, the IP‑SM‑GW should wait for the last Submit report, and translate the last Submit report to an appropriate Instant Message, and forward it to the S‑CSCF.

11) S-CSCF sends the translated Instant Message to the UE.

12) UE acknowledges the translated Instant Message.

13) Acknowledgement of the translated Instant Message is forwarded by S-CSCF to IP-SM-GW.