There are many other cases when a single dialog approach is breaking other things. For instance, the qos module is keeping track of the media connections between the two endpoints. In a single dialog approach, this will not work.
Could you elaborate on this please? I'm wondering because the number of media connections should not change no matter how many spirals there are, no matter whether there is just one or multiple dialogs used to track the spiraled call flow. It will still be just one end-to-end SIP connection with a single media connection.
Just assume that P2 is proxying media using the nathelper module. In this case, the media endpoint are different for the first and the second dialog on P1.
Regards, Ovidiu Sas