Added patch to USSD iteration. Need help to continue.

Hi list, I managed to add interaction to the USSD implemented in the OpenBSC. I attached a patch with the changes realized.The most important changes made are in the ussd.{c, h} files. I implemented the gsm0480_send_ussd_facility. Basically, I copied the gsm0480_send_response, change the GSM0480_OPERATION_CODE field value to GSM0480_OP_CODE_USS_REQUEST, removed the 2 bytes before this field and replaced the GSM0480_MTYPE_RELEASE_COMPLETE byte by GSM0480_MTYPE_FACILITY. Now, I don't know how to proceed. More precisely, I don't know what function is called in the OpenBSC when the user send the response in the mobile phone. Do you guys know the entry point function in this case ? Best Regards