Specifies classes for environmental conditions under which telecontrol equipment has to operate. Gives an overall view of the functional elements contributing to basic structures and to the choice of telecontrol system configurations. It deals with functions which are typical for any process to be monitored and controlled but emphasizes the specific problems which characterize geographically widespread processes, such as the dominant influence of telecommunications links with restricted bandwidth and often low signal-to-noise ratio. However, this report serves only as an introduction to the detailed standards and recommendations laid down in Parts 2-5 of IEC 60870.