The meaning of nat-* DoS settings in realm-config

Hello,

Can you help me please? I am trying to reproduce sip DoS attack from behind a NAT. My purpose is to prove that SBC does not recognize the natted attack if nat-thresholds are not set in the dos-settings of the access realm. There was a trouble in production when SBC forwarded natted attack to a next-hop and that caused an overload of a registrar:

• On the SBC parameters 'nat-trust-threshold', 'max-endpoints-per-nat', 'nat-invalid-message-threshold', 'wait-time-for-invalid-register' are set to 0, i.e. DoS protection for natted hosts is disabled. 'access-control-trust-level' is set to 'low' and 'untrusted-sig-threshold' is set to 4.
• my generator sends few INVITEs to the SBC. Each INVITE has different private IP addresses and ports in the uri-hosts of the header fields 'Via', 'Contact', 'From' and 'To'. In such manner I simulate nat case as if there were lot of terminals with the different private IP addresses behind a NAT device with the single public IP address.