Hello,

We would like to evaluate OpenSER to test interoperability with our sip registrar platform - as our registrar does not handle NAT Traversal we would like to use OpenSER as a mirror proxy . Basically we would like OpenSER to act as an Upper Registrar proxy where all the sip messages would be forwarded to our registrar, based on the domain name used in the Register. ie:
REGISTER 111@domain1.com  -> forward to -> registrar_ip1
REGISTER 222@domain2.com -> forward to -> registrar_ip2
and so on...

If a call is initiated, OpenSER should transparently handle NAT traversal functionalities while forwarding the INVITE request to the proper registrar server.

Below some detailed requirements:
Upper Registration is the capability of a SBC to proxy Registrations towards an upstream Registrar. While it is necessary that all SIP requests traverse the SBC for NAT continuity, Registrations should be allowed to be relayed towards the upstream Registrar while the SBC retains a copy of the AOR and masquerade on behalf of the UA that send the registration request.

Please let us know the best way to configure OpenSER to achieve this type of configuration.

Thanks
SB