Figure 8 shows a simple SCADA system consists of a master unit and a remote unit MTU RTU. The MTU and the RTU shall be equipped with communications equipment to communicate with each other.
Figure 8
In terms of communications equipment necessary to establish communication between the MTU and RTU are known as DCE (Data Communication Equipment). These teams have the ability to make the necessary signals to communicate, that is, encode and decode the signals as required.
An example of such communication devices are modems. In Figure 9 is a diagram of the equipment used.
F ig. 9
The information travels over half from a DTE to another DTE. Modems use a physical medium such as a telephone line or a dedicated line.
The ISO international standards organization has developed a model of OSI open system interconnection. This consists of seven layers (Layers). The function of each layer is defined and used an appropriate number of layers as required. The lower layers are sufficient for most SCADA systems. Note that there is not necessarily a direct correspondence between an OSI layer which defines a function and a physical piece of hardware.
Figure 10 The seven levels of the ISO-OSI model
