6.2.10 RAN Congestion Awareness Function (RCAF)

23.2033GPPPolicy and charging control architectureRelease 17TS

A RAN Congestion Awareness Function (RCAF) is an element which reports RAN User Plane Congestion Information (RUCI) via the Np interface to the PCRF to enable the PCRF to take the RAN user plane congestion status into account for policy decisions. The RCAF sends the RUCI to the PCRFs serving the UEs’ PDN connections as follows:

– For a PDN connection in a non-roaming scenario the RCAF reports the RUCI to the PCRF.

– For a PDN connection in a local breakout scenario, based on operator configuration, the RCAF reports the RUCI to the V-PCRF.

– For a PDN connection in a home routed scenario, based on the roaming agreement with the HPLMN and operator configuration, the RCAF reports the RUCI to the H-PCRF.

NOTE 1: Reporting of congestion information to the HPLMN may be used e.g. in case of a group of PLMNs which belong to a single business entity.

The RCAF determines whether a given PDN connection is served in a local breakout or a home routed roaming scenario based on the APN operator identifier received as part of the APN information from the MME or the S4-SGSN as documented in TS 23.401 [17] and TS 23.060 [12], respectively.

NOTE 2: Operator configuration can be used to limit RUCI reporting on the Np interface to certain APNs only.

In addition if the RCAF detects that a UE is no longer subject to congestion (i.e. the UE is no longer detected in any of the congested cells that the RCAF is monitoring) then the RCAF shall indicate the no congestion state to the PCRFs serving the UE.

Any RUCI changes shall be reported by RCAF unless reporting restrictions apply.

The RCAF maintains a context on per UE and per APN basis. The context is identified by the IMSI and the APN. It contains the following information:

– The previously reported congestion level over the Np reference point.

– The reporting restrictions received from the PCRF. The reporting restrictions are stored by the RCAF until the PCRF explicitly signals to remove the reporting restrictions.

– The logical PCRF id received from the PCRF to identify the PCRF that is the Np destination for the RCAF when sending aggregate messages.