On hardware consisting of the multi-channeled front end of communication that controls the data acquisition process from RTUs are implemented SCADA systems. This is generally done through the repeated short intervals (typically 2 seconds) of polling of RTUs. The obtained data is then redirected to the SCADA server via a local area (LAN) network, allowing operators and other applications to be saved and accessed. User consoles that support the control structure and graphic views of the HMI are used to invoke control. SCADA systems have a redundancy mission criticality which standardizes hot standby fronts and dual LAN applications. Figure shows the general design of a typical SCADA system. The front end supports efficient communications through WAN to the RTUs, for process data collection and transmission to enhance safety and cost saving control commands. A number of setups are supported by contact front ends. This is the most common usage today:

· Multi-drop is a radial configuration that sequences RTUs via a single channel. This leads to a faster response time approach. · Point-to-point Specifies a communication RTU channel. Used for large substations or data concentrators with large I / O requirements. With the addition of multiple communication chains, this configuration provides a high degree of response. A further communication path is added for a reliable line-by-line scheme for applications requiring very high reliability.

· Loop functions in an open loop configuration, each of which is a multiple-drop style tube, from two communication front ends. The gain is reliability, since a standard opening point (NOP) can be surpassed by swapping the loss of any communication segment direction.

· Star Configuration is an RTU Data Concentrator Point to Point combination that controls the RTU slave data access as a point-to – point or Multi-drop-settings. Such configurations are used to economically design mixed response time for distribution automation.

There are many communication protocols in the industry and their variations used between the master station and the RTUs. The central method includes all of them above the Communication Level.