Section: 4.4.12 RAN Congestion Awareness Function
Content: The RAN Congestion Awareness Function (RCAF) is an element that provides RAN User Plane Congestion Information (RUCI) to the PCRF to enable the PCRF to take the RAN user plane congestion status into account for policy decisions. The RCAF collects information related to user plane congestion from the RAN's OAM system based on which the RCAF determines the congestion level (and the identifier) of an eNodeB or E-UTRAN cell. Via the Nq interface the RCAF determines the UEs served by a congested eNodeB or congested E-UTRAN cell and retrieves the APNs of the active PDN connections of those UEs. The decision whether the RCAF operates on eNodeB or E-UTRAN cell level is up to operator configuration. Via the Np reference point, the RCAF sends the RUCI to the PCRFs serving the UEs' PDN connections. NOTE 1: The details of congestion reporting to the PCRF and the Np reference point are specified in TS 23.203[ Policy and charging control architecture ]  [6]. NOTE 2: In the case of roaming or RAN sharing as specified in TS 23.251[ Network sharing; Architecture and functional description ]  [24], Np is an inter-operator reference point. Whether Np applies in the case of roaming and RAN sharing is subject to inter-operator agreements. Figure 4.4.12-1 illustrates the RCAF connected to the MME. The RCAF is located in the same PLMN as the serving MME except in network sharing scenarios where the RCAF belongs to the RAN operator. Figure 4.4.12-1: RCAF connected to MME