This section of IEC 870-5 applies to telecontrol equipment and systems with coded bit serial data transmission for monitoring and controlling geographically widespread processes. It defines basic application functions that perform standard procedures for telecontrol systems. Basic application functions are application procedures that reside beyond layer 7 (application layer) of the ISO reference model for open communication systems. The defined application procedures utilize standard services of the application layer. The specifications of this section serve as basic standards for different companion standards that will be elaborated in detail for specific telecontrol tasks. Each companion standard may use a specific selection of the defined functions. Basic application functions, which are not in this section but are found necessary for defining telecontrol companion standards, should be specified in these companion standards. Only the definition of companion standards will enable interoperability among compatible telecontrol equipment. The general structure of application serv ice data units (ASDUs) used by procedures specified in this section are defined in IEC 870-5-3. Standards specified in this section are compatible with standards defined in sections 1 to 4 of IEC 870-5 (see clause 2).