[SR-Users] Consistent huntable responses based on failure_route question

Hi Kamailio list, I hope you are all well? I am looking for some assistance on a specific error I am trying to work around. Kamailio 5.5.3 - Ubuntu 20.04 Kemi Python script (but I think this is more default failure_route behaviour) Dispatcher module which hunts to a group of FreeSWITCH that I have configured to send 503 responses on. My scenario is fairly simple, I am trying to respond back to a carrier for huntable responses (503 specifically) by calling a failure route below: def ksr_failure_manage(self, msg): if KSR.tm.t_any_timeout()>0 : self.ksr_send_reply_clear_rtpengine(msg, 503, "Timeout to destination") KSR.err("Timeout to Invite for %s from IP %s" % (KSR.pv.get("$ci"),KSR.pv.get("$si"))) return 1 else: self.ksr_send_reply_clear_rtpengine(msg, 503, "Unknown error failover to next node") KSR.err("Failed but not timeout for %s from IP %s" % (KSR.pv.get("$ci"),KSR.pv.get("$si"))) return 1 This works and a 503 with the correct message is sent if the invite doesn't get a response after 2 seconds. (My specific test case here) # Timers for call setup 2 minutes for any 1xx provisional response received # If no invite response received in 2 seconds end the call as per failure route. KSR.tm.t_set_fr(120000, 2000) self.ksr_route_relay(msg) KSR.tm.t_on_failure("ksr_failure_manage") return -255 The issue is after a few more milliseconds after my initial 503 a 408 is sent. Also after the failover if the carrier tries the same Kamailio again it gets a 500 rather than a 408. 408: [cid:image001.png@01D98F15.CD07DCB0] 500: [cid:image002.png@01D98F15.CD07DCB0] My steps to get around this have been to change the default tm code to 503 below, but this has not changed the default response and the above behaviour unfortunately: # ----- tm params ----- # auto-discard branches from previous serial forking leg modparam("tm", "failure_reply_mode", 3) # setting default reason code and response for general errors to allow failover. modparam("tm", "default_code", 503) modparam("tm", "default_reason", "Unknown reason try next node") My question is: How can I make sure my failure route is the final response here. Or if I cannot make sure of this, how can I change the default mapped response to be a consistent SIP response (503 specifically) Many thanks in advance as I am scratching my head on this one a bit. John.