 - the negotiation of the characteristics of real-time transport protocol (RTP) streams via session description protocol (SDP); - the establishment of dedicated bearer to the RTP stream. 3.5.1. Originating side The procedure for establishing the VoLTE session on the outgoing call is described in Figure 3.5. 1) Alice's UA entity generates an initial INVITE request sent to Bob's URI (sip : bob@homeB.net). Alice's UA entity specifies in the header Require that Bob's UA entity must support the precondition of resource reservation before activating the ringing of the telephone. Alice's UA entity indicates in the header Supported that it supports the acknowledgement of provisional responses of 1xx type (value 100rel). VoLTE and ViLTE P-CSCF S-CSCF SIP INVITE SIP 100 Trying SIP INVITE SIP 100 Trying SIP INVITE SIP 100 Trying SIP 183 Session Progress SIP 183 Session Progress DIAMETER AAR DIAMETER RAR GTPv2-C CREATE BEARER REQUEST GTPv2-C CREATE BEARER REQUEST ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST S1-AP E-RAB SETUP REQUEST RRC ConnectionReconfiguration ESM ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfigurationComplete S1-APE-RAB SETUP RESPONSE GTPv2-C CREATE BEARER RESPONSE GTPv2-C CREATE BEARER RESPONSE DIAMETER RAA DIAMETER AAA SIP 183 Session Progress SIP PRACK SIP PRACK SIP PRACK SIP 200 OK SIP 200 OK SIP 200 OK SIP UPDATE SIP UPDATE SIP UPDATE SIP 200 OK SIP 200 OK SIP 200 OK SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing SIP 200 OK SIP 200 OK DIAMETER AAR DIAMETER RAR DIAMETER RAA DIAMETER AAA SIP 180 Ringing SIP ACK SIP ACK SIP ACK Figure 3.5. Establishment of VoLTE session: originating side Alice's UA entity indicates in the header Allow the different supported methods (INVITE, ACK, CANCEL, BYE, PRACK, UPDATE, REFER and MESSAGE). Basic Procedures Alice's UA entity sends an SDP offer in the initial INVITE request to Bob's UA entity. The offer lists the media (audio) that Alice wishes to use for that session and lists the different codecs supported as well. Alice's UA entity indicates in