[SR-Users] Branch variables in branch_failure_route

Paul Smith paul.smith at claritytele.com
Wed Sep 14 16:11:08 CEST 2016

I am struggling to figure out variable scope in branches and branch_failure_routes.  Is there a way to store a variable in a branch route so that I can then read it from the branch failure route if that branch fails?  Also does writing $ru in branch_failure_route append a branch?

For example I have multiple SIP devices registered to Kamailio on the same account credentials.  The devices are behind same NAT, so same public IP.  Some devices have SRTP required and some cannot use SRTP at all, Kamailio does not know in advance of the call whether the call will use SRTP or RTP.

When I send a call to that user Kamailio correctly parallel forks to all the registered devices.  I use rtpengine offer to send SDP with RTP/SAVP in the initial invites.

If one of the devices sends a 488 due to not being able to handle the RTP/SAVP I then want to run rtpengine_offer with RTP/AVP and send another invite to the same  device.  

In the branch failure route I seem to have to read the current $ru and then write it back into $ru before calling t_relay() or I get 
Sep 14 14:56:06 registrar-secure /usr/sbin/kamailio[10168]: ERROR: tm [t_fwd.c:1771]: t_forward_nonack(): ERROR: t_forward_nonack: no branches for forwarding

This code seems to work, but it feels like I’m doing something very wrong…. in particular $avp(triedrtpout) is set for the transaction, I should be setting it separately for each branch.  
event_route[tm:branch-failure:SRTP] { # Handle failure response
        xlog("L_INFO", "Handling $T_reply_code response to $rm to ru: <$ru> and du: $du\n");

        if(t_check_status("488") && is_method("INVITE")) {
                if ($avp(triedsrtpout)==1) {
                        # set $ru seems to create a new branch ... even when we set it to its current value.
                        # we want to generate a new SIP INVITE to the same AOR but with different SDP
                        xlog("L_INFO","488 caught. Resending to $ru");
                        # try with unencrypted RTP/AVP
                        rtpengine_offer("to-tag trust-address replace-origin replace-session-connection ICE=force RTP/AVP");
                        if (!t_relay()) {


I am using kamailio 4.2 debian package for this registrar.

Sorry for the rambling question … I don’t understand enough to write the short version!


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