Hi,
did you already research the mentioned protocols?
GED-125 is the IVR PG protocol.
GED-145 is the Application Gateway protocol.
You are a server, listening for and replying to client requests (the client is ICM, or rather, the ICM Router Application Gateway subprocess in case of GED-145 and the VRU PG PIM subprocess in case of GED-145).
Based on what you wrote, GED-125 is the protocol you need to use.
G.