An Application Server entity in an IP Multimedia Subsystem (IMS) network comprises an interface for interfacing with an application and control logic which is arranged to inspect signalling information received from the application via the interface in the form of Extensible Markup Language (XML). The received signalling information is compared with stored rule data which specifies a relationship between an element in the signalling information and an action that should be taken and output data is generated based on the comparison. The Application Server can output operational measurements and/or charging information which more accurately reflect usage made of the Application Server resources. The need for a separate OSA/Parlay-X gateway can be avoided.