[SR-Users] Wrong To tag in t_reply

Daniel-Constantin Mierla miconda at gmail.com
Fri Dec 11 14:06:14 CET 2020


actually you are wrong that you think it is a wrong to tag. The entity
that generates the final reply sets the to-tag (e.g.,to be able to match
ack). Even here where you talk about the serial forking, you are going
to face the case of different to-tag values for each branch sent out and
replied. But also think about parallel forking, that timed out with many
active branches, which to-tag to use?!?

So think that kamailio itself is the branch of the incoming request, and
can create many outgoing branches. If it generates a final reply, it
does it to the incoming branch. It is not forwarding (sending back) a
reply from an outgoing branch.

Obviously, being open source, one can code a specific behaviour for some
specific needs, but is not SIP specs compliant. If the upstream cannot
deal with different to-tags, it won't really work with serial/parallel
forking anyhow.

As a side remark, seeing the comments, if
route(ROUTE_ELEMENT_FINAL_FAILURE) is used only in failure_route, then
transaction is always defined there, because failure_route is executed
only in the transaction context. Anyhow, if you are using in many
places, not knowing if transaction was created, you can use send_reply()
to avoid any test in the config.


On 11.12.20 11:04, Ivan Ribakov wrote:
> Hi all,
> I’m trying to implement following routing behaviour:
> - ingress INVITE is sequentially forked to 1 or more endpoints
> - under certain conditions sequential forking may be stopped and
> pre-defined error returned to the caller
> Here’s is part of the config responsible for handling errors:
> }
> # We need to check if the error happens before the first egress,
> because T-state is not defined yet so we can not use t_reply
> if ($var(before_first_egress) == 0) {
> t_reply("$var(sipCode)", "$var(sipMessage)");
> } else {
> sl_send_reply("$var(sipCode)", "$var(sipMessage)");
> }
> }
> Here is a simple scenario where delivering call to first endpoint
> times out after receiving 180 Ringing (using custom fr_inv_timer
> value) where:
> - .33 is caller
> - .208 is Kamailio
> - .138 is callee
> Notice that 504 is retransmitted by Kamailio. Here is a comparison of
> 180 and 504 returned by Kamailio:
> As can be seen, 180 was proxied from the callee and has callee’s
> to-tag (tag=CALLEE1), however 504 that was generated by Kamailio using
> t_reply() has a different to-tag (presumably generated by Kamailio).
> How can I tell Kamailio not to generate new to-tag but to use the last
> one that proxied back to the caller?
> Thanks in advance for any help!
> Regards,
> Ivan
> _______________________________________________
> Kamailio (SER) - Users Mailing List
> sr-users at lists.kamailio.org
> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users

Daniel-Constantin Mierla -- www.asipto.com
www.twitter.com/miconda -- www.linkedin.com/in/miconda
Funding: https://www.paypal.me/dcmierla

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