IEC 60870-4:1990 pdf download.Telecontrol equipment and systems
3.4 Security
The security of a telecontro! system can be defined as its ability to avoid placing the controlled system
in a potentially dangerous or unstabie situation. it deais with the consequences of faiiures， arising out of maifunctions of the telecontrol equipment， undetected information errors as well as information losses .
The consequence of a failure may depend on the state of the power system at the instant of failure. A dangerous situation can arise out of a combination of a failure of the telecontroi system with a particuiar situation of the power system. in such cases, the probability of occur-rence of a dangerous situation is the product of the probability of occurrence of the failure and the probability of occur rence of the particular situation in the power system， provided that the two occurrences are independent of each other.
Measures to enhance the security are given in appendix A,clause A.4.
3.5 Data integrity
Data integrity is defined as the unchangeability of an information content between a source and its destination. In telecontro! systems,data integrity concerns the probability of undetected errors res ulting in wrong information about actual process states in the monitoring direction or unintended actions in the controi direction of the system.
Data integrity classes are provided which specify upper limits of undetectable information error p robabilities, on the path from an information source to its destination, covering data acquisition,processing and transmission. 1 I he error probabilities take into account the residual error probabilities (IEV 371-08-06) and the probability of residuai information iosses (IEV 371-08-10) .
Publication 870-5-1 of this series of standards specifies in sub-clause 4.1 three data integrity classes for quantified upper limits of undetected message errors ( " residual message errors")，depending on the bit error rate on the transmission channei. This way of specifying data integrity classes for telecontrol transmission channeis is necessary because the environmentai conditions causing disturbances on trans-mitted data are to a great extent unpredictable and the means of protecting data against undetectable errors by coding methods are
limited.
3.6.4 Telecounting (transmission of integrated totais)
integrated totais are supplied to the telecontrol equipment in the form of digital coded values or as incremental pulses which are added together in interna! counters. The storage command for the integrated totals may come from the local counter units， or may be transmitted. to the outstation by an interrogation command. It should be ensured that the further processing of the data be managed in iess than, a given time and that the storage command be sent simultaneously to a specified number of outstations.IEC 60870-4 pdf download.