GW-2 entity. SIP/2.0 183 Session Progress Content-Type: application/sdp Content-Length: (...) C=IN IP4 190.1.15.2 m=audio 12538 RTP/AVP 97 98 The SIP 183 Session Progress message is forwarded without changing the SDP message to the IBCF-1 instance. 6) The IBCF-1 instance forwards to the P-CSCF entity the SIP 183 Session Progress message, whose SDP message replaces the RTP stream characteristics received from the IBCF-3 instance with those provided by the entity TrGW-1. 232 VoLTE and ViLTE SIP/2.0 183 Session Progress Content- - Type application/sdp Content-Length - : (...) C=IN IP4 192.0.2.2 m=audio 9452 RTP/AVP 97 98 The SIP 183 Session Progress message is forwarded without changing the SDP message to Alice's UA entity. 8.2.1.2. Terminating side The session establishment procedure for the nominal routeing of the RTP streams, relating to the outgoing call, is described in Figure 8.6. Table 8.2 summarizes the IP addresses and the port numbers of the RTP streams, established, on the one hand, between Bob's UA entity and TrGW-4 entity, and, on the other hand, between TrGW-3 and TrGW-4 entities. P-CSCF IBCF-6 IBCF-5 S-CSCF IBCF-4 SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK Figure 8.6. Session establishment for nominal routeing terminating side Roaming 233 Bob's UA TrGW-4 IP address 193.0.2.1 193.0.2.2 Port number 49170 TrGW-4 TrGW-3 IP address 179.15.1.1 191.1.15.2 Port number 62111 12538 Table 8.2. RTP flow characteristics in the case of nominal routeing terminating side 1) Upon receipt of the SIP INVITE request from Alice's home network, the IBCF-4 instance generates the SIP INVITE message to the S-CSCF entity, whose SDP message contains the RTP stream characteristics provided by the TrGW-3 entity. INVITE <sip:+46107197378@operatorY;user=phone;iotl=homeA-homeB> SIP/2.0 Content-Type application/sdp Content-Length: (...) C=IN IP4 191.1.15.2 m=audio 12538 RTP/AVP 96 97 2) The S-CSCF entity