[Serusers] help! lost invites when using outbound proxy

[jeff kwong]

Hi everyone!

I have set up a ser as an outbound proxy with nathelper+rtpproxy. This
is my set up

IPphone1 --> 
                    nat router --> outbound proxy(OP) --> softswitch(SS)
IPphone2 -->

with the OP and SS in public. The IPphones are behind the same NAT and
both configured to the same OP.  I am only testing against this
softswitch from some vendor so i don't  have any control over it. And
I used the sample nathelper.cfg from the CVS to get started.

Registration went smoothly. The problem starts when I try to call one
phone using the other. Nothing happens until I recieve a 408 request
time out. I did dumps on the OP and
NAT router and what happens is the that the SS sends the INVITE to the
NAT router directly instead of sending it to the OP. I tried reading
the RFC but since im still new with sip and ser i am still at lost.
Maybe someone here can help enlighten me. On sending INVITES, where in
the SIP messages does the SS knows where to send the INVITE? Is it
suppose to send back on what's in the Contact Header in registration?
Would a Record-Route help solve the problem? Here's a rough
description on what happens on the INVITES on phone1 calling phone2:

IPphone1 --> NAT --> OP                 --> SS 
                                Adds: Via                 
                                Changes Contact with source ip

IPphone1 <-- NAT <--  OP                  <-- SS
    407         407        407                     407
                                Removes Via

IPphone1 --> NAT --> OP                   --> SS
Invite with                  Adds Via
Authorization             Changes Contact with
                                source ip

           (lost) NAT <------------------------------ SS
             sees 3 Vias

Thanks in Advance for any help or ideas.

Regards,
CGR