6.15 Service-level Interworking: CPM capable UE sends a Chat session invitation to an SMS user

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

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

6.15.1 IP-SM-GW in the originating network

Figure 6.15.1: Chat session invitation to SMS user and Message data exchange (IP-SM-GW in originating network)

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

2) The UE sends a session invitation request for a chat session to the S-CSCF, using the appropriate SIP method. The UE may request to hide its Public User Identity from the recipient within the session invitation.

3) S-CSCF forwards the session invitation to the 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 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. If the sender of the session invitation asks 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 in all messages it sends to the recipient. If operator policy prohibits anonymity, the IP-SM-GW shall not perform interworking and shall send back an appropriate response.

NOTE 2: Steps 5 to 7 are only executed if the operator policy is to check back with the SMS user before accepting the invitation on behalf of the SMS user. Otherwise, the process continues with step 8, as if the SMS user has responded with an acceptance of the chat session invitation.

5) Otherwise, the IP-SM-GW correlates an MSISDN to this chat session. Any SMS sent from the SMS user to this MSISDN should be interworked into the chat session with which this MSISDN is correlated. 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 chat session invitation request to a Short Message (SMS- SUBMIT) carrying an SC Address, then forwards it towards the SMS-SC (SC Address) via the SMS-IWMSC (as described in TS 23.040 [2]). The text in the Short Message is defined by the operator and should convey information to the SMS user that he is invited to send and receive messages in the context of a chat session, and include instructions on how to accept, reject and end the session. If no response is received in time, the IP-SM-GW will consider the session rejected and send an appropriate response to the session invitation.

NOTE 3: The MSISDN used as the sender of the Short Message is either the MSISDN of the CPM user or one that is assigned by the IP-SM-GW, depending on operator configuration.

6) The SMS-IWMSC forwards the Short Message (SMS- SUBMIT) to the SMS-SC and the SMS is delivered to the SMS user using standard SMS procedures (see TS 23.040 [2]).

7) A Short Message is sent by the SMS user via the SMS-GMSC to the IP-SM-GW in accordance to steps 2 to 4 and steps 10 to 13 from clause 6.14.

8) If the answer is positive, the IP-SM-GW acknowledges the session invitation. Otherwise the IP-SM-GW will consider the session rejected and send back an appropriate response.

9) Session invitation acknowledgement is forwarded by S-CSCF to the CPM UE.

NOTE 4: The following steps are executed only if an SMS with a positive answer is received from the SMS user or if the operator policy indicated that the session is accepted without SMS user interaction. If a negative response to the invitation is received or if no response from the SMS user is received within an operator defined time, the IP-SM-GW will send a negative response to the chat invitation.

NOTE 5: Steps 10 to 12 are repeated for each message sent from the CPM user towards the SMS user, and steps 13 to 14 are repeated for each message sent from the SMS user towards the CPM user.

10) The CPM user sends a message within the chat session containing data to the recipient SMS user.

11) The IP-SM-GW transforms the received message into a Short Message and sends a Short Message (SMS- SUBMIT) carrying the SC Address, then forwards it towards the SMS-SC (SC Address) via the SMS-IWMSC (as described in TS 23.040 [2]). According to operator policy, each SMS generated for the SMS user may include text instructions on how to leave the chat session.

12) The SMS-IWMSC forwards the Short Message (SMS- SUBMIT) to the SMS-SC and the SMS is delivered to the SMS user using standard SMS procedures (see TS 23.040 [2]).

13) A Short Message is sent by the SMS user via the SMS-GMSC to the IP-SM-GW in accordance to steps 2 to 13 from clause 6.14.

NOTE 6: Step 5 of the flow in clause 6.14 becomes this: The IP-SM-GW identifies that a session exists between the SMS user and the CPM user.

6.15.2 IP-SM-GW in the terminating network

The SMS user (SMS UE B) in this flow is a CPM user (CPM user B) whose preferences are set in his home network to receive his incoming chat sessions as Short Messages.

Figure 6.15.2: Chat session invitation to SMS user and message data exchange (IP-SM-GW in terminating network)

1) The originating network for CPM user A sends a session invitation request for a chat session to a CPM user (CPM user B) in another IMS domain, using the appropriate SIP method. The UE may request to hide its Public User Identity from the recipient within the session invitation. The originating S-CSCF (not shown) resolves the destination domain and routes the session invitation towards the S-CSCF in the terminating network ("terminating S-CSCF").

2) The terminating S-CSCF forwards the session invitation to the 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.

3) Authorization to continue is checked. If the sender of the session invitation asks 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 in all messages it sends to the recipient. If operator policy prohibits anonymity, or if the IP-SM-GW cannot identify the sending party and the operator prohibits session invitations from unidentified users, the IP SM GW shall not perform interworking and send back an appropriate response.

4) The IP-SM-GW performs service-level interworking by converting the chat session invitation request to a Short Message. The IP-SM-GW obtains the routeing information for the destination UE from the HLR/HSS.

5) The IP-SM-GW sends the Forward Short Message message to the target MSC. The IP-SM-GW assigns an MSISDN representing the chat session to ensure that the reply to this SMS is sent back to this particular IP-SM-GW. Any SMS sent from the SMS user to this MSISDN should be interworked into the chat session with which this MSISDN is correlated. The text in the Short Message is defined by the operator and should convey information to the SMS user that he is invited to send and receive messages in the context of a chat session, and include instructions on how to accept, reject and end the session. The identity of the original sender (CPM user or group) is included as part of the operator provided invitation text. If no response is received in time, the IP-SM-GW will consider the session rejected and send an appropriate response to the session invitation.

6) The MSC/SGSN/MME/SMSF sends the Short Message to the SMS user.

7) A Short Message is received via the SMS-GMSC from the SMS user by the IP-SM-GW, in accordance to steps 2 to 4 and steps 10 to 13 of clause 6.14, indicating the response to the chat session invitation. The message is targeted to the MSISDN representing the chat session which was assigned in step 5.

8) If the answer is positive, the IP-SM-GW acknowledges the session invitation. Otherwise the IP-SM-GW will consider the session rejected and send back an appropriate response.

9) The session invitation acknowledgement is forwarded by S-CSCF to the CPM UE.

NOTE 3: The following steps are executed only if an SMS with a positive answer is received from the SMS user or if the operator policy indicated that the session is accepted without SMS user interaction. In case a negative response to the invitation is received or if no response from the SMS user is received within an operator defined time, the IP-SM-GW will send a negative response to the chat invitation.

NOTE 4: Steps 10 to 13 are repeated for each message sent from the CPM user towards the SMS user, and step 14 is repeated for each message sent from the SMS user towards the CPM user.

10) The CPM user sends a message within the chat session containing data to the recipient SMS user.

11) The IP-SM-GW transforms the received message into a Short Message and obtains the routeing information for the destination UE from the HLR/HSS.

12) The IP-SM-GW sends a Short Message (SMS- DELIVER) towards the MSC/SGSN/MME/SMSF, as described in TS 23.040 [2]. The IP-SM-GW inserts the MSISDN representing the chat session as the sender of the message, to ensure that the reply to this SMS is sent back to it.

13) The MSC/SGSN/MME/SMSF forwards the Short Message (SMS- DELIVER) to the SMS user, and the SMS is delivered to the SMS user using standard SMS procedures as described in TS 23.040 [2]).

14) A Short Message is received via the SMS-GMSC from the SMS user by the IP-SM-GW, in accordance to steps 2 to 13 from clause 6.14. The message is targeted to the MSISDN representing the chat session which was assigned in step 5.

NOTE 5: Step 5 of the flow in clause 6.14 becomes this: "The IP-SM-GW identifies that a session exists between the SMS user and the CPM user".