Automation networks

Looking at the CIM model, we can understand how important information being exchanged between devices on the same or different levels is. In the lower levels, we have a large amount of simple information that is exchanged within small and determined time intervals. At higher levels, we need to transfer less information that is more complex and within longer time intervals that are not necessarily determined. In an integrated production system, different types of IT networks are needed, each tailored to the task to which it is dedicated. We can identify three categories of networks—information network, control network, and field network, as follows:

• Information network: This ensures the communication between the control devices and the applications and devices that manage the plant and the company. It is a network that must be able to process complex information that is composed of many bytes. This information is exchanged with low frequencies and there is no need to ensure that the message is delivered within determined time intervals. It is common to use Ethernet for the first two levels of the OSI model and TCP/IP protocols for the third and fourth.
• Control network: This must ensure the communication between the devices dedicated to the control and supervision of the plants. The information that's sent is not very complex, but the transmission has to be within determined time intervals and at higher frequencies. The control networks are usually developed by the PLC makers, and their implementation is proprietary. This means that the other devices in these networks can talk with the PLCs through specific network cards and programs for interfacing. For these networks, the first two levels of the OSI model are typically based on a token to ensure the determinism in the transmission. The software for network management is usually integrated into the system provided by the PLC maker, which allows the user to configure the network by configuring the physical connections between the nodes by assigning a logical address to each of them. Over the last few years, the market has been driving a standardization process for the control networks through formal or de facto standards and also using Ethernet for the first two levels of the OSI model. 
• Field network: The networks dedicated to the field or fieldbuses, as they are commonly referred to, have been introduced to act as interfaces for the smart sensors and actuators to the control devices, as they have basic computation capabilities. We will discuss fieldbuses further in the next section.