[Users] forking call to another user on same proxy

[Christian Schlatter]

I try to fork a call to another user registered at the same proxy as the 
caller. I figured out that the easiest method would be to use the 
append_branch() function, something like

route[0] {

	if (method=="REGISTER") { save("location"); exit; }

	if (!lookup("location")) {
		sl_send_reply("404", "Not Found");
		exit;
	}

	# if someone calls test2 at domain, fork call to test4 at domain
	# (test2 and test4 are both registered at domain)
	if (avp_check("$rU", "eq/test2")) {
                 append_branch("sip:test4 at 127.0.0.1");
         }

	if (!t_relay()) {
                 sl_reply_error();
         };
         exit;
}

I know that this could also be achieved by adding permanent location 
records, but I'd like to load the forking targets from a DB in the 
future. So my first question would be if using

append_branch("sip:test4 at 127.0.0.1");

is the correct way to do parallel forking to a local user.

I'm asking because this method does not work for me as expected. It 
seems that the two UAC state machines running on the same proxy host 
that are involved in a forking call do somehow not work well together.

Forking the INVITE to both test2 and test4 works well, but when I pick 
up test2 the call gets terminated after a few seconds. Further 
investigations have revealed that canceling the second call leg does not 
work correctly. There is a message flow diagram available at 
http://www.unc.edu/~cschlatt/openser.html .

For some reason, the proxy process sending from 127.0.0.1 is 
retransmitting the 487 "Request Terminated" although it receives ACKs 
from the upstream proxy. And this causes the upstream proxy to send a 
487 back to the caller (time 15.360), which then terminates the call 
established between caller and test2.

And this only happens if I fork to the same proxy, if I use two proxy 
hosts everything works fine (??).

Any advice is highly appreciated,

Christian