The SMSIP UE has received the Short Message as described in clause 6.11 and sends a Delivery report (SMS-DELIVER-REPORT) to the IP-SM-GW via the S-CSCF.
This procedure describes the delivery of an Instant Message to a registered or an un-registered IMS subscriber. For the unregistered case, the S CSCF forwards the Instant Message to the IP SM GW based on the unregistered iFC of the subscriber.
UE submits an Instant Message, destined to another IM user or CPM user in another IMS domain, 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] and in OMA-TS-CPM_Conv_Fnct-V1_0 [17].
The IM AS or CPM AS can forward the Instant Message back to the terminating S-CSCF, e.g. the terminating IM user is offline or the CPM user has no terminating interworking user preferences.
In the case of the CPM AS, if terminating interworking user preferences are set, the Instant Message is routed directly to the IP-SM-GW in which case the procedure continues with step 7.
If the user is authorized, the IP-SM-GW performs service-level interworking by converting the Instant Message to Short Message. The IP-SM-GW shall obtain the routeing information for the UE from the HLR/HSS and deliver the message to the UE. 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 anonymise 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.
The SMS GMSC interrogates the HSS 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.
The IP-SM-GW creates a MT Correlation ID as per TS 23.040, which associates the Routing Info retrieval with the subsequent Forward Short Message messages(s), and stores this along with the IMSI of the receiving subscriber. The IP-SM-GW returns to the SMS-GMSC the address of itself, along with the MT Correlation ID in the IMSI field, as routeing information.
The SMS-GMSC delivers the Short Message to the IP-SM-GW in the same manner that it delivers the Short Message to an MSC, SGSN, MME or SMSF, including the MT Correlation ID received from the IP-SM-GW, in place of the IMSI.
If the user is authorized for service-level interworking, the IP-SM-GW converts the Short Message to an Instant Message. It sends the Instant Message using the appropriate SIP method towards the S-CSCF.