SAP) via the interconnect border control function (IBCF) in the case of IMS interconnection or via breakout gateway control function (BGCF) and MGCF entity in the case of CS interconnection. The RTP stream is transmitted to the PSAP emergency center via TrGW in the case of IMS interconnection or via IMS GW in the case of CS interconnection. In the case of IMS interconnection, the IBCF entity ensures the anchor point of the SIP stream. In the case of IMS interconnection, the TrGW entity ensures the anchor point of the RTP stream. In the case CS interconnection, the MGCF entity ensures the anchor point of the SIP stream. 260 VoLTE and ViLTE In case of CS interconnection, the entity IMS GW entity ensures the anchor point of the RTP stream. 9.2.2. Procedures 9.2.2.1. Registration The registration procedure implementing the e-SRVCC function is shown in Figure 9.12. 1) The ATCF entity transfers the SIP REGISTER request to the I-CSCF entity by inserting the Path header containing the PATH URI identity and the header Feature - Caps with the following parameters: - +g.3gpp. atcf: this parameter informs the session transfer number for SRVCC (STN-SR); -+g.3gpp.atcf-mgmt: this parameter contains the URI identity of the ATCF entity; - +g.3gpp.atcf-path: this parameter contains the identity PATH URI identity of the ATCF entity; - +g.3gpp.srvcc-alerting: this parameter indicates that the MSC Server entities support the SRVCC function during the ringing phase. REGISTER sip:home1.net SIP/2.0 Feature-Caps: *;+g.3gpp.atcf="<tel:+1-237-888-9999>"; +g.3gpp.atcf-mgmt-uri = <sip:atcf.HomeA.net>" +g.3gpp.atcf-path="<sip:termsdgfdfwe@atcf.HomeA.net>"; +g.3gpp.mid-call; +g.3gpp.srvcc-alerting Path:<sip:termsdgfdfwe@atcf.HomeA.net>,<sip:aga2gfgf@pcs f1.HomeA.net:5070;ob> . . . 2) In the second registration phase, when the mobile has been authenticated, the ATCF entity includes in the message SIP 200 OK, the Header Feature-Caps with the parameter +g.3gpp.atcf containing STN-SR number. SIP/2.0 200 OK Feature-Caps: - *;+g.3gpp.atcf="<tel:+1-2