Hi,
After asking many questions, I haven't got any clues about how Kamailio handles INVITE message by default, in terms of modifying c= line in SDP
When client register, SIP proxy will call nat_uac_test() to detected if client is NATed or not, then save this info.
When client A calls client B, the INVITE message will go through SIP proxy. Here the SIP proxy can do 3 things (as in section "INVITEs behind NAT" in the pdf).
1. Add an SDP command direction:active to the SDP content
2. Change the c= line to a.b.c.d
3. Force RTP to go through a proxy by changing the c-line to c=IN IP4 address-of-proxy and the m-line to
m=audio port-on-proxy RTP/AVP 0 101.
When will SER do 2, 3 ?
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Khoa PhamHCMC University of Science
Faculty of Information Technology