[SR-Users] In-dialog BYE request, how to return back to original sender ?

Hi list, I'm facing an routing issue with the following sip infrastructure: ASTERISK 1 ---\___ Kamailio proxy ____ Kamailio frontend ___ IPBX ASTERISK 2 ---/ And please find below desired call-flow: 1 - An asterisk 1 server send a call to a proxy 2 - This proxy make a location lookup, and send it to kamailio frontend proxy 3 - Frontend proxy relay to Wazo PBX (for example) 4 - Callee respond ... 5 - Callee hangup the call, so Wazo PBX send a BYE request to kamailio frontend proxy 6 - Based on Route headers, frontend forward BYE request to proxy 7 - ... here cames issues ... Question is simple (but answer will be probably more complex): how can i sent in dialog BYE request to ASTERISK 1, and not asterisk 2. Should i use dispatcher module ? Should i use specials headers to send back to Asterisk 1 the BYE request ? What is the normal behaviour for in-dialog requests ? I can't find any answers on SIP RFCs or any archived messages on mailing list. Thanks in advance, Best regards.