A cellular traffic monitoring system includes: a Traffic Detection Function (TDF) module to monitor cellular traffic associated with a cellular subscriber device, and to generate application detection output indicative of an application used by the cellular subscriber device; an application-based charging module to generate, based on the application detection output of said TDF module, application-based charging data related to said cellular subscriber device; a Policy Charging and Enforcement Function (PCEF) module to enforce one or more charging rules that are Service Data Flow (SDF) based and are related to said cellular subscriber device; an SDF-based charging module to generate SDF-based charging data related to said cellular subscriber device; and a charging correlator module to identify a potential over-charging due to an overlap between the application-based charging data and the SDF-based charging data.