Sunday, October 3, 2010

Legacy Network of SCADA Protocols





The existing SCADA protocols share certain characteristics that make them highly reliable in what might be described as "a strong heritage but older" network.

These networks are often used at very low speed i.e. 300 - 1200 bits per second. The data is usually asynchronous (there is no time synchronization) and remote terminal unit through the poll of single multi-point circuits. All of these polls and responses must occur within a short time is often measured in fractions of minutes.

Currently, to meet the higher demand for data, SCADA equipment manufacturers, system designers and users start looking for higher speed devices. There are very large infrastructure telephone lines, private cable and microwave operating on sound frequency classes, where there are approximately 3000 hertz bandwidths. This is enough to pass for example 9600 bps modem quick poll. Fast poll modems in 1200 to work as a modem to the extent that they pass the data through grade voice lines, telephone lines using four-wire and works in multi-drop fashion.

In addition, a new faster network, and protocol they interact with existing SCADA protocols and present some interesting challenges. Network protocols such as frame relay, Ethernet, and IP, each has a sensitive characteristic time delay will result, causing a short gap in the data, or not to send multiple Data Carrier Detect (DCD) signal transitions. This delay can lead to SCADA protocols to consider error in the link. In this case can be resolved, then there are many new and faster communications networks are available.


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