The present document provides the stage 3 specification of the Gx reference point. The functional requirements and the stage 2 specifications of the Gx reference point are contained in 3GPP TS 23.125 [3]. The Gx reference point is for provisioning service data flow based charging rules between the Traffic Plane Function (TPF) and the Charging Rules Function (CRF)@ also known as Service Data Flow Based Charging Rules Function. The present document defines: ? the protocol to be used between TPF and CRF over the Gx reference point; ? the information to be exchanged between TPF and CRF over the Gx reference point. Whenever it is possible the present document specifies the requirements for this protocol by reference to specifications produced by the IETF within the scope of Diameter. Where this is not possible@ extensions to Diameter are defined within the present document