[Serusers] How to catch re-invite and signal rtpproxy ??

Hi all: I am using ser 0.8.14 with rtpproxy and kphone 0.4.1.1, When kphone holds the call, then unholds later, sometimes kphone will change the rtp port in SDP differ from previously used. Therefore, the rtp packet can't be forward correctly via rtpproxy if ser doesn't signal rtpproxy to change the forwarding port mapping I have asked before about this problem, and Zeus Ng have give me some information that the key factor is to catch the re-invite, but i don't know how to verify if a INVITE is really a INVITE or r reINVITE... Is there any method can let ser catch or verify the re-invite message in ser.cfg ? Thanks and regards Jimmy