ted services to which the user has subscribed. Control Network IP/SIP services with: Security Charging Combinations Mobile convergence connectivity network router Internet Figure 14.16 The IMS domain position. IP networks used to be stupid in the central network part, but with IMS we are heading towards a central intelligence again Proxy CSCF (P-CSCF) - the P-CSCF, which contains a very limited CSCF function, is the only Internet multimedia function placed in the network being visited; that is, when the subscriber's unit is roaming outside of its home network. The P-CSCF con- tains address translation functions in order to proxy the session request directed at the I-CSCF in the home network. Figure 14.17 shows possible CSCF locations. The upper half of the diagram shows the UE served at the home network and the lower half of the diagram shows the UE roaming to a visited network. Home network P-CSCF S-CSCF I-CSCF Visited Home network network P-CSCF S-CSCF I-CSCF Figure 14.17 CSCF locations for mobile-terminated sessions Understanding Changing Telecommunications - Building a Successful Telecom Business The MRF performs multiparty call, multimedia conferencing and transcoding functions. It is responsible for bearer control (with, for example, the GGSN and MG) in the case of mul- tiparty/conference sessions. The MRF is also responsible for performing announcement functions. The MRF communicates with the CSCF for call control of announcements and conferences. The MRF is separated in two logical functions: MRC (media resource con- trol) and MRG (media resource gateway). The MRG is the media-related part, co-located with the MG. The MRC is the control part, which can be located with the server nodes. MGC controls call-related state information that pertains to the call connection in the media gateway. The MGCF communicates with the CSCF for call information. It requests the media gateway to handle the bearer connection. See Figure 14.15. 'A call between a mobile roaming subscriber and for example, an ISDN subscriber, ma