Architectural View

This diagram is an architectural view of the control and user planes, depicting communication both before and after transfer. This depiction assumes the PGW and the P-CSCF are in the serving network and support IMS voice roaming (if not the home network). So, the ATCF resides in the serving networking (home network if not roaming). The access leg of the session is divided into the serving leg and home leg. In an actual network, there might be other server IMS nodes.