client1 <> provider <> kamailio <> asterisk <> client2
when client1 calls client2, everything seems to work. sounds works.
after a few seconds the call gets terminated.
after tcpdump syslog and config checks i figured out that asterisk sends 200 OK through kamailio to the provider, after this the provider sends a ACK to kamailio, kamailio however sends this ACK to itself and not to asterisk.