A flight information service and an alerting service are the basic levels of air traffic service, providing information pertinent to the safe and efficient conduct of flights and alerting the different relevant authorities should an aircraft be in distress. These are available to all aircraft through an FIR. Higher levels of air traffic advisory and control services may be available within certain portions of airspace within an FIR, according to the ICAO class of that portion of airspace (with regard to national regulations), and the existence of a suitably equipped authority to provide the services.