<p dir="ltr">In that case, the answer to your question seems to be that the UDP packets did not reach the OpenSIPS server, because nothing was added to the OpenSIPS logs using debug level 4. All of this seems to point to the cause being UDP packet fragmentation. Is this correct? </p>
<div class="gmail_quote">On 17 May 2016 4:24 pm, "Bogdan-Andrei Iancu" <<a href="mailto:bogdan@opensips.org">bogdan@opensips.org</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<tt>The TCP/IP stack of your server may decide to drop an UDP packet
if it cannot re-assemble it correctly (like not all the IP fragments
were received).<br>
In such a case, you see the IP packets (carrying the fragments) on
network level, but they are never delivered at application level.<br>
<br>
Regards,<br>
</tt>
<pre cols="72">Bogdan-Andrei Iancu
OpenSIPS Founder and Developer
<a href="http://www.opensips-solutions.com" target="_blank">http://www.opensips-solutions.com</a></pre>
<div>On 17.05.2016 16:05, Nabeel wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">The
next question - is this INVITE reaching your opensips script ?
to be sure that the OS delivers the UDP packet to the opensips
application.</blockquote>
<div><br>
</div>
<div>I don't have any firewall on my server. Why would the UDP
packet get blocked between entering the server and reaching
opensips script? The opensips server is running without
errors. Other calls work fine.</div>
</div>
</blockquote>
<br>
</div>
</blockquote></div>