[Serusers] On Reply Processing Question

Hi, The manual explains that we can use "t_on_failure" and "failure_route" primitives to route a SIP request to another destination if the original destination does not answer. It is very clear to me how this would work for an INVITE message which receives a confirmation from the far end (like "Trying"). But when the call is established, the originating party sends an ACK message which is not supposed to receive a reply. How does SER know where to send this ACK to?? Does it again try the first destination? If so then the message will be lost. And how about INFO messages (like those used to send DTMF tones). Lets say a call is established to a backup gateway using "failure_route". Then the user sends a DTMF tone as an INFO message (maybe he called an IVR). How does SER know that this INFO message must go to the backup gateway? If SER tries the main gateway first for every single DTMF digit pressed then this is not going to work properly. Thanks, Ricardo Villa