Hi Eleni,
ETC implies that the 3GPP OCS (HPLMN) is connecting to a gsmSRF/assisting_gsmSSF.
Looks like it is trying to setup a session to send an announcement menu.
I would ask the HPLMN operator to explain their current setup with their OCS solution.
VBR/ Wallis Dudhnath
Note: OCS: Online Charging System that is used for Realtime Charging for Voice (CAP V2 / V3) and Data (Gy).