I have an issue with some upstream carriers quickly replying with 100 Trying but then basically times out.

I'm looking for a good solution to distinguish between the 100 reply and any other replies, and alter the timeout values. My goal is to be able to re-route calls where the 180/183 is not received within a few seconds, and if the 180/183 is received I'd like to give the call a much longer timeout.

I realize there is a "fr_inv_timer" that would do this, but I would not like to set that to low since I fear it would affect many other call types, i.e. if a carrier would send 183 once but for some reason does not resend on regular intervals.

I'm on Kamailio 4.1 and my current settings are:

fr_timer : 2000

fr_inv_timer : 120000

restart_fr_on_each_reply : 1

The only solution I can think of is to update the fr_inv_timer in an on_reply-route if the reply code is 180/183 but I'm not sure that would even work? Is that the way to go or is there another way?

Thanks in advance!

/Tobias