I've dealt with the same issue, and as far as I understand, the problem is with Freeswitch not supporting branching and IIRC not recognizing that the via branch has changed.  Adding a sleep function as indicated in that link is a blocking process, so if you have this serial forking occur frequently it could cause kamailio to have issues.  There is a non-blocking async_sleep function that I didn't have success with, but that was probably a misunderstanding of how it worked on my part.    With that said, you might try adding another sip_profile to your freeswitch server (on a different port) and see if sending the serially forked call to the other sip_profile addresses it.  Otherwise, I'd recommend adding another freeswich instance (even if it's on the same server) rather than calling sleep();

Regards,

Kaufman

---

From: Alex A via sr-users
Sent: Wednesday, March 19, 2025 4:58 PM
To: sr-users@lists.kamailio.org
Cc: Alex A
Subject: [SR-Users] How to place a delay between cancelling branch and retrying next one on timer expiry?

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Hi All,

I have an interesting use-case where I need to place a delay between cancelling branch and retrying next one.

Background:
Running Kamailio 5.6.x

Kamailio routes requests via a freeswitch B2BUA server on select call flows (where B2BUA functionality is required).
Call flow examples:
PSTN --> Kamailio --> Freeswitch --> appserver1
PSTN --> Kamailio --> Freeswitch --> appserver2

On attempt failures, a branch retry is required from appserver1 to appserver2; however freeswitch B2BUA remains the same
Since Freeswitch does not quite follow the RFC 3261 timer K specifications (should be 0 seconds for reliable transports, but FS keeps transactions for T4 (set to 2 seconds));
I have implemented an artificial delay in failure route before retrying (as per recommendation described here: https://freeswitch-users.freeswitch.narkive.com/TsSye66D/482-request-merged-in-serial-forking-solved )

Script config:

onreply_route[MANAGE_REPLY] {

xlog("L_INFO", "reply $T_reply_code received");

if (t_check_status( "1[1-9][0-9]")) {

t_reset_fr();

} else {

t_set_fr(120000);

}

}

route(NATDETECT);

#!ifdef WITH_RTPENGINE

route(RTPMANAGE);

#!endif

}

route[RELAY] {

if (is_method("INVITE|BYE|SUBSCRIBE|UPDATE")) {

if(!t_is_set("branch_route")) t_on_branch("MANAGE_BRANCH");

}

if (is_method("INVITE|SUBSCRIBE|UPDATE")) {

if(!t_is_set("onreply_route")) t_on_reply("MANAGE_REPLY");

}

if(is_method("INVITE|BYE|UPDATE|CANCEL|ACK")) {

setflag(FLT_DLGINFO);

}

if (!t_relay()) {

sl_reply_error();

}

exit;

}

route[TOCARRIER] {

process bunch of things, attach custom headers, generate request URI

t_on_failure("MANAGE_FAILURE_CARRIER");

route(RELAY);

}

failure_route[MANAGE_FAILURE_CARRIER] {

xlog("L_INFO", "reply $T_reply_code received");

if ($avp(inbound_attempt)<=1){

if ($dlg_var(b2bua)=="true"){

usleep(1900000);

}

route("TOCARRIER");

}

Call Flows:

The above fix works well when an explicit error reply is received back.

error reply SIP exchange:
SBC --> INVITE(branch0) ---> Freeswitch
SBC <-- 503 <-- Freeswitch
failure_route executed (sleep runs here)
SBC --> INVITE(branch1) ---> Freeswitch
call continues as expected.



however does not work when NO reply is received at all and the timer expires.
Current timer expiry SIP exchange:
SBC --> INVITE(branch0) ---> Freeswitch
SBC <-- 100/180 <-- Freeswitch
SBC (timer expires)
failure_route executed (sleep runs here)
SBC --> INVITE(branch1) ---> Freeswitch
SBC <-- 482 Merged  <-- Freeswitch
SBC --> CANCEL(branch0) ---> Freeswitch


I am looking to CANCEL branch0 before the sleep delay runs


Based on source code, t_cancel_branches("this") can only be executed in reply_route;
however the chellenge is that reply_route never sees the "faked 408" on timer expiry(although the failure route does see $T_reply_code 408).



Any suggestions on how to handle this would be greatly appreciated.

TIA