Hello, Base on my testing OPTION pings  can be sent only to UDP nated clients. So it is impossible with kamailio to send OPTION pings to TCP/TLS nated clients? I found doc for some version of nathelper module  where the natping _tcp parameter can be set by modparam("nathelper", "natping_tcp", 1) Unfortunately, this parameter cannot be used in default nathelper module in kamailio 4.2.(doc is probably from OpenSIPS)  I would like to send OPTION pings to TLS nated and individualy selected user agents. Does exist some possibility to do it with kamailio 4.2? If not by default does exist the possibility to compile and build kamailio with the nathelper module mentioned above (with natping_tcp parameter)? Or does exist some other solution? Thank you in advance Petr