Hi, I have have Kamailio as SBC one-end is SRTP and other end is RTP

So I m using 

rtpengine_manage("replace-origin replace-session-connection DTLS=passive OSRTP-offer ICE=force SRTP")

rtpengine_manage("replace-origin replace-session-connection DTLS=off SDES-off ICE=remove RTP")

1-Asterisk(RTP) -----2-Kamailio/RTPEngine ------ 3- Carrier with SRTP

I detect source IPs and to manage this all. 

When call is made from 1 to 3 all works and during call 3 send re-Invite to Hold Call .. We need to call 

How shall I detect that 1- if this is Re-Invite (has_totag() )and 2- its from Callee.