n is described in Figure 9.3 in the case where the MSC server entity and the mobile do not implement the ICS service. When the MSC server entity receives the call for the establishment of the communication, it recovers from the SCC AS entity, via camel application part (CAP), the IP multimedia routing number (IMRN). The MSC server entity routes the call to the media gateway control function (MGCF) using the IMRN number to reach the SCC AS entity. The MGCF entity translates the telephone signaling: - ISDN user part (ISUP) at CS network side; - SIP at IMS network side. VoLTE and ViLTE Ut (XCAP) (DIAMETER) (CAP) (DIAMETER) (ISUP) Mg (SIP) Mx / Mi (SIP) Server NAS (CM) H.248 (CS flow) Mb (RTP flow) Figure 9.3. MSC server and UE not implementing ICS function functional architecture The MGCF entity provides the control of the IMS GW entity for the establishment of the CS bearer on one side and the RTP stream on the IP network side. The B2BUA function of the SCC AS entity allows to end the dialogue with the MGCF entity and to start a new dialogue with the called party. 9.1.2. Procedures 9.1.2.1. Registration The registration of the mobile to the IMS network deploys the general procedure if the mobile implements the ICS function. In the case where the mobile and the MSC server entity do not implement the ICS function, the mobile is not registered to the IMS network. The registration procedure of the mobile to the IMS network is described in Figure 9.4, where: - the MSC server entity implements ICS function; - the mobile does not implement ICS function. 1) After the attachment of the mobile, the MSC server entity transmits the SIP REGISTER request to the I-CSCF (interrogating-CSCF) entity. Service Centralization and Continuity 247 The SIP URI (Uniform Resource Identifier) of the REGISTER request is derived from the mobile country code (MCC) and the mobile network code (MNC). The temporary public identity of the headers From and To is derived from the international mobile subscriber identity (IMSI). The private identity in