B.1 Service-level interworking: IM or CPM user initiates a group chat and sends an Instant Message to a group list including SMS users

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

The flow in this clause is the same as that described in clause 6.15.1 with the difference that it is required that the IP-SM-GW assign an MSISDN for this group chat session so that it is clear for the SMS user that any message sent to the assigned MSISDN will be delivered to the group chat session participants, not just to the CPM UE that invited the SMS user.

In this flow, the IP-SM-GW is in the PLMN of the CPM UE, but it could also be in the PLMN of the SMS user if that user was also a CPM user and had terminating user preferences to deliver the session invitation via SMS.

Figure B.1: CPM user initiates a group chat and messages are exchanged within the group chat via service-level interworking

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

2) The UE generates a chat session invitation which includes group information, e.g. Group identifier in the Request-URI and/or recipient list in the body of the chat session invitation. UE submits the Instant Message to the S-CSCF using an appropriate SIP method.

3) Based on the stored iFC, S-CSCF forwards the session invitation to an AS in charge of handling group chat requests, e.g., the controlling function server defined in OMA-TS-SIMPLE_IM-V1_0 [12] or the controlling function server defined in OMA-TS-CPM_Conv_Fnct-V1_0 [17].

4) The group chat AS replicates a session invitation per recipient according to the group information it obtains acting as a B2BUA. See details in OMA-TS-SIMPLE_IM-V1_0 [12] or in OMA-TS-CPM_Conv_Fnct-V1_0 [17].

5) The group chat AS sends the generated multiple session invitations to the S-CSCF.

6) The group chat AS forwards one of the chat session invitations to the IP-SM-GW according to normal routing procedures (e.g., via S-CSCF).

NOTE 1: Nodes specific to the CPM functions such as ISF are either collocated with the IP-SM-GW or else are not shown.

7) The IP-SM-GW translates the chat session invitation request to a Short Message (SMS- SUBMIT) and forwards it towards the group chat SMS-SC (SC Address) via the SMS-IWMSC (as described in TS 23.040 [2]). The IP-SM-GW assigns an MSISDN representing the group 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 will be interworked into the group chat session with which this MSISDN is correlated. The text in the Short Message is defined by the operator and conveys information to the SMS user that he is invited to send and receive messages in the context of a group chat session, and includes 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.

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

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

10) If the answer is positive or if operator policy is to accept the session invitation on behalf of the SMS user, the IP-SM-GW acknowledges the session invitation. Otherwise the IP-SM-GW will consider the session rejected and send back an appropriate response.

11) The session invitation acknowledgement is forwarded by S-CSCF to the group chat AS.

12-13) The group chat AS responds back to the group chat session initiator once the first user joins the group chat session.

NOTE 2: 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 shall send a negative response to the chat invitation.

14-17) The IP-SM-GW subscribes to the participant information changes.

NOTE 3: Steps 18 to 21 are repeated for each message sent from any group chat session participant towards the SMS user, and steps 22 to 24 are repeated for each message sent from the SMS user towards the group chat session participants.

18) The CPM UE (or any group chat session participant) sends a message containing data to the group chat AS.

19) For the group chat session participant who is an SMS user, the message is routed towards the IP-SM-GW.

20) The IP-SM-GW identifies that a session exists between the SMS user and group chat AS and transforms the received message into a Short Message and sends a Short Message (SMS- SUBMIT) carrying the SC Address, then forwards it towards the group chat SMS-SC (SC Address) via the SMS-IWMSC (as described in TS 23.040 [2]). The IP-SM-GW inserts the address representing the group chat session as the sender of the message to ensure that the reply to this SMS is sent back to this particular IP-SM-GW.

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

22) A Short Message is received from the SMS user via the SMS-GMSC 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 group chat session which was assigned in step 7.

NOTE 4: 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. Steps 6 and 7 of the flow in clause 6.14 are replaced by steps 23 and 24 in this flow.

23) The IP-SM-GW identifies that a session exists between the SMS user and the group chat AS and transforms the received message into message data and sends it within the session towards the group chat AS.

24) The group chat AS forwards the message to all group chat participants.