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<p><tt>Hi Cinthia!</tt></p>
<p><tt>The default opensips.cfg file [1] also provides all commonly
used cases for t_check_trans() [2]:</tt></p>
<p><tt>* to detect and handle SIP request retransmissions<br>
* to match hop-by-hop ACKs (i.e. ACKs to negative SIP replies,
codes 3xx-6xx). These ACKs are not routed per se -- rather
OpenSIPS processes them but generates its own version of the ACK
when replying upstream, so the script handling is different.<br>
* to test if a CANCEL actually matches an INVITE. If it
doesn't, you'd probably want to drop it.</tt></p>
<p><tt>To conclude: it's fine to call t_check_trans() right at the
top of the script. Make sure you save the return code for later
use inside the has_totag() block (mid-dialog requests).</tt></p>
<p><tt>Best regards,<br>
</tt></p>
<p><tt>[1]:
<a class="moz-txt-link-freetext" href="https://github.com/OpenSIPS/opensips/blob/master/etc/opensips.cfg">https://github.com/OpenSIPS/opensips/blob/master/etc/opensips.cfg</a><br>
[2]:
<a class="moz-txt-link-freetext" href="https://opensips.org/html/docs/modules/3.0.x/tm.html#func_t_check_trans">https://opensips.org/html/docs/modules/3.0.x/tm.html#func_t_check_trans</a><br>
</tt></p>
<pre class="moz-signature" cols="72">Liviu Chircu
OpenSIPS Developer
<a class="moz-txt-link-freetext" href="http://www.opensips-solutions.com">http://www.opensips-solutions.com</a></pre>
<div class="moz-cite-prefix">On 12.09.2018 19:50, Cinthia Leung
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CA+J76DiXWnrEP3VUD=FLGRBNWR1QiQ1E4mNaM0umTcLxqOuAew@mail.gmail.com">
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<div dir="ltr">Hi all!
<div><br>
</div>
<div>Traditionally t_check_trans() is used in the "new requests"
and specific part of the in-dialog section. I wonder if it's
OK to put it right at the top most of the script. Thanks.</div>
<div><br>
</div>
<div><br>
</div>
<div>Cindy</div>
</div>
<br>
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</blockquote>
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