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

[Jan Henkins]

Hi,

Sorry that I cannot answer your question, but this particular issue has
been bothering me the past few days, so I would also like to know wether
this can be accomplished. A solution will cure a lot of ills! :-)
Especially in places where bandwidth comes at huge premiums for hosted
solutions (yes, alas these places still exists). The use of rtpproxy or
similar will then unfortunately mean that bandwidth usage will more than
double (SIP and media stream x2) for each call, which will ensure
massive bandwidth bills (not something you want for a service that is
supposed free for it's users). Does somebody have a possible solution,
please?

On Mon, 2005-12-05 at 16:45 -0800, S G wrote:
> 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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-- 
Regards,
Jan Henkins
Cell: +27-84-951-4334