Monitoring and Control of processes are implemented using SCADA systems. SCADA is an acronym for Supervisory Control and Data Acquisition. Variables of a process are constantly monitored and processed for computation of various parameters for issue of control commands, if necessary, in both open and closed loop manner with the help of a combination of electromechanical and digital elements/equipments.

The implementation of fairly large SCADA system used in applications like power system monitoring and control, involves a centralized process computer connected to a large number of Remote Terminal Units (RTUs) which are geographically distributed in vast areas, using efficient communication channels. The process computer acquires intelligence from these remote terminal units and does the necessary processing internally with the help of numerous application software programs that are executed in the computer either on demand basis.

The Power system Dispatchers are responsible for the dispatch operations like, issue of supervisory controls to either open or close Circuit Breakers (C.Bs) in substation, lower or raise the scheduled interchange of power with the neighboring power systems, to maintain system parameters like voltage, frequency, power flow, to monitor and analyze various system alarms as well as to take appropriate actions against each alarm etc.

In order to enable the Dispatchers to do these functions, they are provided with a complete snap-shot of the entire power system with the help of various sub-station oriented displays in several computer consoles. The sub-station oriented displays in several computer consoles. The sub-station level data acquisition such as status of CB's, disconnectors, / isolators and analog values such as MW, MVAR, Hz, KV, Amps etc. are first captured with the help of respective interfacing elements in the RTU.

Master station scans the RTUs either on cyclic fashion or on poll-by-exception method. Depending on the communication channel that exists between Master and RTU's, the exchange of data between the Master and RTUs are implemented using either analogue or digital communication media. The Characteristics of transfer of data between Master and the RTUs is typical of a Master/ Slave protocol, in a SCADA system. There exists a variety of different types of Master/ Slave protocols that are implemented in a SCADA system. Most of these protocols in the past were only supporting analog communication channels. However, with the advent digital communication technology, getting migrated to digital SCADA protocols like IEC60870-104 protocols supported using digital communication media. This would also support an RTU talking to more than one Master Station.