Ring back is sent from trm end to org end. Does call ever connect and do you get 2way voice? If the answer is yes, then most likely your org device is not set correctly and needs to open the media path on ringing. If you do not get voice in both directions, then you need to look at the config of your CR and test direct to the end device to see if there is port blocking.
II am not sure about the setup that you are using . But in order for the ringback to be through , pls check whether the priginating end is receiving a response to the SETUP request , from the far end . The response to the initial setup request should put the media through for the ringback tone.