[OpenSIPS-Users] Where to call t_check_trans

[Liviu Chircu]

Hi Cinthia!

The default opensips.cfg file [1] also provides all commonly used cases 
for t_check_trans() [2]:

* to detect and handle SIP request retransmissions
* 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.
* to test if a CANCEL actually matches an INVITE.  If it doesn't, you'd 
probably want to drop it.

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).

Best regards,

[1]: https://github.com/OpenSIPS/opensips/blob/master/etc/opensips.cfg
[2]: https://opensips.org/html/docs/modules/3.0.x/tm.html#func_t_check_trans

Liviu Chircu
OpenSIPS Developer
http://www.opensips-solutions.com

On 12.09.2018 19:50, Cinthia Leung wrote:
> Hi all!
>
> 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.
>
>
> Cindy
>
>
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> Users at lists.opensips.org
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