Surrogate configuration is not working on a new 6300 Deployment

Good Afternoon.

 

We have a new SBC 6300 deployment; we configuured on it the surrogate agent configuration as we had on a 4250 equipment, but until this momment the SBC only makes this:

 

IPPPBX<==>options<==>SBC==>register==>P-CSCF.

 

The P-CSCF sent back the 401 registration challenge but the SBC never replies with a REGISTER which includes the authentication information (attached its the trace).

 

This is what we have configured:

 

session-agent (P-CSCF)
        hostname                                172.31.212.6
        ip-address                              172.31.212.6
        port                                    5060
        state                                   enabled
        app-protocol                            SIP
        transport-method                        UDP
        realm-id                                IMS-SBC-CORE
        allow-next-hop-lp                       enabled
        constraints                             disabled
        ping-method                             OPTIONS;hops-0
        ping-interval                           60
        ping-send-mode                          keep-alive

session-agent (IPPBX)

        hostname                                10.11.255.2
        ip-address                              10.11.255.2
        port                                    5060
        state                                   enabled
        app-protocol                            SIP
        transport-method                        UDP