[Serusers] How to Minimize rtp proxy usage for all cases including when behind the same NAT

[S G]

Hello,

I have SER setup to only use the rtpproxy if the client is behind a 
symmetric NAT. This is accomplished by using STUN since STUN will not modify 
the contact headers if it detects a symmetric NAT. So SER see's the local 
address in the contact header and only forces rtpproxy for those types of 
call. When users are behind the same NAT then ser detects this using AVP's 
and force_rtpproxy is not used for the call. This only works when STUN is 
not enabled. Since when STUN succeeds the orignal local address of the phone 
is changed to the public address in the sip message. So when two STUN 
enabled clients try to call each other from behind the same nat the call 
fails. The call fails because the NAT does not support harpin of media as 
most don't. The only way this call would work is if the contacts could be 
changed back to use their local addresses pre-STUN. How can SER be 
instructed to use the local address for calls behind the same NAT when STUN 
is enabled? One way I can think of doing this is to change nathelper to 
extract the original IP from the VIA header and rewrite the SDP. In the SIP 
trace i see only IP's in contact headers and SDP are changed when STUN 
succeeds. Is there a simpler way to accomplish this?


Thanks,
Sumeet

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