ionComplete S1-AP E-RAB SETUP RESPONSE GTPv2-C CREATE BEARER RESPONSE GTPv2-C CREATE BEARER RESPONSE DIAMETER RAA DIAMETER AAA SIP 200 OK Figure 3.9. Adding a video stream: initiated side 1), 2), 3) Alice's UA entity (or Bob's) forwards the UPDATE request to the domain homeB. net (or homeA. net). The UPDATE request can be replaced by the re-INVITE request and contains a new SDP offer on both audio and video streams. The S-CSCF entity controls that Alice's UA entity (or Bob's) is authorized to establish a ViLTE session. Basic Procedures 4), 5) The 200 OK response to the UPDATE request contains the SDP response in which Bob's UA entity (or Alice's) retains a codec from those proposed by Alice's UA entity (or Bob's). 6) to 15) Upon receipt of the 200 OK response, the P-CSCF entity initiates the establishment of dedicated bearer for the video stream. 16) The P-CSCF entity forwards the 200 OK response to Alice's UA entity (or Bob's). The procedure of the addition of the video stream for the ViLTE session, at the received side, is described in Figure 3.10. P-CSCF S-CSCF SIP UPDATE SIP UPDATE SIP UPDATE SIP 200 OK DIAMETER AAR DIAMETER RAR GTPv2-C CREATE BEARER REQUEST GTPv2-C CREATE BEARER REQUEST ESM ACTIVATE DEDICATE EPS BEARER CONTEXT REQUEST S1-AP E-RAB SETUP REQUEST RRC ConnectionReconfiguration ESM ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfigurationComplete S1-AP E-RAB SETUP RESPONSE GTPv2-C CREATE BEARER RESPONSE GTPv2-C CREATE BEARER RESPONSE DIAMETER RAA DIAMETER AAA SIP 200 OK SIP 200 OK Figure 3.10. Adding a video stream: received side 1), 2), 3) The UPDATE request received from the domain homeA. net (or homeB net) is transmitted to Bob's UA entity (or Alice's). The S-CSCF entity controls that Bob's UA (or Alice's) is authorized to establish a ViLTE session. 4) Bob's UA entity (or Alice's) selects a codec for the video stream among the proposals received in the SDP offer associated with the UPDATE request. VoLTE and ViLTE The UA entity responds with 200 OK message containing the select