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<p>Dear OpenSIPS-users,</p>
<p><br>
</p>
<p>First of all, happy new year.</p>
<p>I'm still reading about NATs, SIP proxies and SIP, to understand how to solve a question in my project. I'm not expert in TCP, IP, routers, NATs and networks. That is why I would like to get some help here. I guess I'm almost getting the point to solve
it.<br>
</p>
<p><br>
</p>
<p>In my current network topology case I have:</p>
<p><br>
</p>
<p><br>
</p>
<p> Mobile Phone 1 on Internet</p>
<p> / \ |<br>
</p>
<p> | |</p>
<p> | SIP |</p>
<p></p>
<p> | \/ Real IP (Internet)</p>
<p> NAT ------------------------------------------------
<br>
</p>
/\ | 'Nated' IP (Wan)<br>
<p></p>
<p> | |</p>
<p> | SIP |</p>
<p> | |</p>
<p> | |</p>
<p> | \/ </p>
<p> ROUTER ------------------------------------------------
<br>
</p>
<p> /\ | (Lan) <br>
</p>
<p> | SIP |</p>
<p> | |</p>
<p> SIP Proxy OPENSIPS</p>
<p> | |</p>
<p> | SIP |</p>
<p> | |</p>
<p> Mobile Phone 2 on local network <br>
</p>
<p><br>
</p>
<p><br>
</p>
<p>When Phone 2 calls Phone 1, everything is ok. Phone 1 is registered on OpenSIPS with 'Nated' IP, by someway. So, Phone 2 sends INVITE to such IP. When Phone 1 answers with SIP OK, the Contact header filed has the same 'Nated' IP. Then, Phone 2 can send the
ACK to the correct path.</p>
<p><br>
</p>
<p>However, when Phone 1 calls Phone 2 and Phone 2 answer with SIP OK, Phone 1 can't send the ACK, because the Contact header field from SIP OK has the local IP for Phone 2.</p>
<p>It is true because when Phone 2 registers itself on OpenSIPS, the local IP is recorded in the local database table.</p>
<p><br>
</p>
<p>So I have the following questions:</p>
<p><br>
</p>
<p>1 - Can this problem be solved without using the Nat Traversal Module?</p>
<p><br>
</p>
<p>2 - Can NATHELPER module fix the Contact header field (as a I saw this module has functions related with it), when Phone 2 sends SIP OK to Phone 1? If yes, how can such module determine a 'good' IP to put in this header field?</p>
<p><br>
</p>
<p>3 - If Phone 2 uses a stun server, will such phone be registered on OpenSIP with a real IP, won't be? Could it be a solution too?</p>
<p><br>
</p>
<p>Any hint will be very helpful!</p>
<p><br>
</p>
<p>Thanks a lot!</p>
<p><br>
</p>
<p> <br>
</p>
<p><br>
</p>
<p><br>
</p>
<p><br>
</p>
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