7 4) The IBCF entity of the HomeB. net network transfers to the I-CSCF entity the INVITE message including the SDP message which replaces the characteristics of the RTP streams received from the IBCF entity of the HomeA. net network with those communicated by the TrGW entity of the HomeB. net network. The I-CSCF entity retrieves from the HSS entity the identity of the S-CSCF entity and forwards the INVITE message without changing the SDP message. 196 VoLTE and ViLTE INVITE ip:+46107197378@operatorHb.net;user=phone;iotl=homeA- homeB> SIP/2.0 Content-Type: application/sdp Content-Length: (...) C=IN IP4 190.1.15.2 m=audio 12538 RTP/AVP 97 98 5) I-CSCF entity receives the provisional response 183 Session in Progress from the S-CSCF entity with the associated SDP message containing the RTP streams characteristics of Bob's UA entity. SIP/2.0 183 Session Progres Content-Type: application/sdp Content-Length: (...) C=IN IP4 190.1.15.1 m=audio 24152 RTP/AVP 97 98 The I-CSCF entity forwards to the IBCF entity of the HomeB net network the provisional response 183 Session in Progress without changing the SDP message. 6) The IBCF entity of the HomeB net network transfers to the IBCF entity of the HomeA. net network the provisional response 183 Session in Progress including the SDP message which replaces the characteristics of the RTP streams received from Bob's UA entity with those provided by the TrGW entity of the HomeB. net network. SIP/2.0 183 Session Progress Content-Type: application/sdp Content-Length: (...) C=IN IP4 178.15.1.2 m=audio 33248 RTP/AVP 97 98 7) The IBCF entity of the HomeA. net network transfers to the BGCF entity the provisional response 183 Session in Progress including Interconnections the SDP message which replaces the characteristics of RTP streams received from the IBCF entity of the HomeB. net network with those communicated by the TrGW entity of the HomeA. net network. SIP/2.0 183 Session Progress Content-Type - application/sdp Content-Length: (...) C=IN IP4 192.0.2.2 m=audio 56743 RTP/AVP 97 98 Ha