A charging system includes a rating engine, a session control module, and a charging unit determination module. The session control module receives a request for service units, associated with a charging session, from a client or service element, and obtains one or more input parameters from the request for service units. The charging unit determination module obtains account data associated with the request for service units, determines at least one charging session related parameter based on the one or more input parameters and/or the account data, and pass the at least one charging session related parameter to the rating engine. The rating engine grants service units based on the at least one charging session related parameter, and forwards an indication of the granted service units to the session control module for return to the client or service element.