[SR-Users] kamailio as proxy for sipclients behind NAT without rtpproxy

I want to use kamailio as a forwarding proxy infront of SIP registrar like asterisk/freeswitch without any rtpproxy to reduce the load on server and to be able to handle more requests . I am using default kamailio config file registration is working fine but call is not connecting . So sip clients should register on asterisk(or freeswitch) and able to receive inbound calls too . I am interested in only REGISTER & INVITE messages to restrict the messages based on sipclient's source ip . Please can someone help me with a working configuration for this setup . This is the topology .. (Sipclients with or without NAT ) ---------> (Kamailio without rtpproxy)-------------->(Asterisk or freeswitch or anyother sipserver )