ntity. The SIP message also contains the instances 1 and 2 of the a=visited-realmpopulated with the following information: - the domain name to which Alice's UA entity is connected (va.operatorV.net), the IP address and the RTP stream port number of Alice's UA entity; - the domain name of the network to which the IBCF-1 instance is connected (xa1.operatorX.net), the IP address and the port number of the RTP stream provided by the TrGW-1 entity for the specified domain name. INVITE SIP: tel:+4687197378; SIP/2.0 Route:<sip:scscf1.operatorH.net;lr;iotl=visitedA-homeA> Content-Type: application/sdp Content-Length: (...) C=IN IP4 178.15.1.1 m=audio 62111 RTP/AVP 96 97 a=visited-realm: Va. .operatorV. net IN IP4 192.0.2.1 49170 a=visited-realm: Xal.operatorX.net IN IP4 178.15.1.1 62111 238 VoLTE and ViLTE 4) The IBCF-2 instance forwards to the S-CSCF entity the SIP INVITE message, whose SDP message replaces the RTP stream characteristics received from the IBCF-1 instance with those provided by the TrGW-2 entity. The SIP message adds the instance 3 of the header a=visited-realm populated with the domain name of the network to which the instance IBCF-2 is connected (Ha.operatorH.net) the IP address and the port number of the RTP stream provided by the TrGW-2 entity for the specified domain name. INVITE SIP: tel:+4687197378; SIP/2.0 Route:<sip:scscf1.operatorH.net;lr;iotl=visitedA-homeA> Content-Type: application/sdp Content-Length: (...) C=IN IP4 190.1.15.1 m=audio 16789 RTP/AVP 96 97 a=visited-realm: Va.operatorV. net IN IP4 192.0.2.1 49170 a=visited-realm: Xal.operatorH.net IN IP4 178.15.1.1 62111 a=visited-realm: Ha.operatorH.net IN IP4 190.1.15.1 16789 5) The S-CSCF entity transfers to the IBCF-3 instance the SIP INVITE message whose header Feature-Caps indicates that the loop to Alice's visited network is activated. The S-CSCF entity withdraws its URI identity in the Route header and adds that the TRF entity of the visited network, indicating in the iotl parameter the direction of the request (homeA-visitedA). INVIT