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

According to rtpproxy flow
http://kamailio.org/docs/ser-getting-started/SER-GettingStarted.pdf

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 ?

-- 
Khoa Pham
HCMC University of Science
Faculty of Information Technology
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