Re: How to correctly generate a 181 Call is being forwarded reply?

Loose_route() does not check transaction but route headers if any.

You are trying to do b2bua operations with kamailio by sending 181 through it (hence it will create a to-tag that does not belong to no one and will never be used after).

It's typically a kind of action you can't/shouldn't/must not do in kamailio.

Le 1 déc. 2025 15:14, Benoit Panizzon via sr-users <[email protected]> a écrit :

Hi again

> I don't seem to get it working as expected - still trying to figure out

> what and where the call fails.

I think I have found what goes wrong.

A => B => CFW => C

C has MIN-SE: 900

A is initially sending Sestion-Timer: 600

Without 181 reply:

C replies with 422 Timer too Small Min-SE: 900

This 422 Reply has a ToTag.

A re-initiates the call with a larger session timer, that INVITE has NO

ToTag - new transaction. The Calls succeeds.

Now I repeat the same, but I send a 181 message back to A BEFORE A

receives the 422 from C. That 181 has a ToTag.

Now when A re-initiates the INVITE, it includes the ToTag received in

the 181 and loose_route fails as there is no such transaction.

Is A misbehaving by including a ToTag when it should not? Should the 181

reply not contain a ToTag?

I again tried all variants

* sl_send_reply() generates ToTag

* send_reply() generates ToTag

* t_reply() does not send the reply.

Mit freundlichen Grüssen

-Benoît Panizzon-

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