Hello!
I have my own backend and start looking for call with call.route message. I take it from billid and every other messages are looking for this billid. But when I use call.execute to dumb/ there is no billid, so I decide to add it when dispatch call.execute message with param 'add_billid'=='true'. Also when calling to fork, there is billid in call.route message, but not in call.ringing and call.answered so I add some changes to code to add it.
I have done a patch. Sorry if my code is bad. I'm not good in C++. Also I don't know everything about Yate and maybe my solutions is not correct.