One of the things that was requested at the start of the outbound work in Kamailio was the ability to "force" outbound even when a UA does not support it and to be able to use the outbound flow tokens for NAT traversal instead of contact aliasing on "single server" configurations.
fine IF there is some advantage in putting the information in rr header instead of contact header.
The argument that was presented was that putting the information in the rr header is more aligned with published standards.
I have come across a number of devices at interconnects that incorrectly strip parameters that they do not recognise from the Contact-URI. While this is clearly incorrect behaviour on their part getting operators and vendors to fix their equipment is not always possible.
As I said, I do not have a need for this myself as I plan to use separate edge proxies and registrars - but I can see where the requirement came from.
To my mind this means we need to double-RR when there is just a single proxy/registrar in use. It also means that, when there is a single proxy/registrar and the Path extension would not normally be used, we still need to do something to get the flow tokens (userinfo part of the Path-URI) into the location table so that they can be used for NAT traversal.
sounds much more complicated than contact aliasing.
Indeed. But I can see where it is sometimes needed.
Peter