This technical report applies to telecontrol equipment and systems with coded bit serial data transmission for monitoring and control of geographically widespread processes. This report is intended as a brief tutorial on transmission techniques, equipment and protocols in view of their use in telecontrol systems. It is thus intended as a guide to orient those using the standards defined in the series of IEC 870-5 and IEC 870-6. More precisely, it gives a frame of reference for evaluating solutions as well as defining and describing the key technical terms. Terms that are defined in IEC 50(371) and in IEC 870-1-3 are complemented by further definitions in clause 3 of this report.It further provides:û descriptions of applicable basic communication technologies;û basic rules as to how different system layers (see clause 3) can be used together (i.e. which combinations of standards in different layers are technically coherent and which are not).It is not intended to recommend or impose solutions, this being the role of IEC 870-5 and IEC 870-6.