Section: 4.4.3 IMS support
Content: IMS support for 5GC is defined in TS 23.228[ IP Multimedia Subsystem (IMS); Stage 2 ]  [15]. The 5G System architecture supports N5 interface between PCF and P-CSCF and supports Rx interface between PCF and P-CSCF, to enable IMS service. See TS 23.228[ IP Multimedia Subsystem (IMS); Stage 2 ]  [15], TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45] and TS 23.203[ Policy and charging control architecture ]  [4]. NOTE 1: Rx support between PCF and P-CSCF is for backwards compatibility for early deployments using Diameter between IMS and 5GC functions. NOTE 2: When service based interfaces are used between the PCF and P-CSCF in the same PLMN, the P-CSCF performs the functions of a trusted AF in the 5GC.