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. The use-case I have for outbound involves having the edge proxies and registrars as separate devices. I don't have a need for "single server" myself at the moment. I don't mind putting a bit of extra work in to support it - but only if there is a genuine need for it and someone available to test it. My understanding of outbound NAT traversal is that in the forward direction of the dialog the first edge proxy adds the flow token to the first Record-Route (the RR it adds) to indicate where the request came from, and the last edge proxy copies the flow token from the last Route header (as added by the registrar supporting Path) into the last Record-Route (the RR it adds). This means that the route-set for the dialog now contains two flow tokens with covers all of the information that would previously have been encoded in the Contact-URIs in the initial request and the final response to that request. 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. This means additional work will be needed for the edge proxy (in the RR module) which is the part I am working on, and the registrar which is the part others have been working on. Regards, Peter -- Peter Dunkley Technical Director Crocodile RCS Ltd

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. Indeed. But I can see where it is sometimes needed. Peter -- Peter Dunkley Technical Director Crocodile RCS Ltd

Peter Dunkley writes: i can try what happens when i register an outbound ua to a co-located outbound proxy/registrar and let you know if i see some problems. -- juha