[Kamailio-Users] Trying to deliver a call across multiple peers with t_relay

[Tyler Brauer]

Good morning/afternoon/evening! I'm trying to accomplish two things.

* First, I'd like to try sending a call from our B2BUA through
Kamailio to one of our SIP peers, but in the event that the peer is
unreachable, try the same call across an alternate peer. I'm currently
trying something in our routing block like this.

if(!t_relay("udp:1.1.1.1:5060","0x2"))
{
	if(!t_relay("udp:2.2.2.2:5060"))
	{
	 	 xlog("L_INFO", "Could not complete");
	}
}

I've also been trying to put together something similar using
t_on_failure(#) and a failure_route[#] block to say "if the first
t_relay fails, try this instead". In both instances, when fr_timer
elapses because the first peer hasn't responded to an INVITE, I can't
stop Kamailio from throwing a "SIP/2.0 408 Request Timeout" back to
the B2BUA.

I have tried setting the flag on t_relay to keep quiet in the event of
a forward failure, and instead use something like sl_send_reply("181",
"Call Is Being Forwarded") to say to the agent "hold on, we're still
trying". I can't seem to find the syntax to make any of that work. The
408 still keeps getting delivered (in spite of the flag on t_relay) to
our server, which causes it to stop trying to deliver the call through
Kamailio.

* The second thing I'd like is that if the first two peers are
unavailable, the request is rewritten to go across a third peer as a
PSTN call. (eg: a call tries to reach 101 at 1.1.1.1 fails, then
101 at 2.2.2.2 fails, so then 2015551234 at 3.3.3.3 is tried). This requires
rewriting the username field of the request URI, but I'm not sure how
to do that without confusing the originating server.

Could anyone help with the config syntax to resolve either of those
two problems? Thank you very much!