Another important thing :
that my SIP conversation :
User --------> OpenSER --------> Asterisk
User -INVITE-> OpenSER OpenSER-INVITE->Asterisk Asterisk -Trying-> OpenSER Asterisk -Session progress-> OpenSER OpenSER -Session progress-> User Asterisk -service unavailable-> OpenSER OpenSER-ACK->Asterisk OpenSER -service unavailable-> User User -ACK-> OpenSER
My endless t_relay is this ACK user to openser.