The components of an ICS network are often described as an operational technology (OT) network, in contrast to an IT network, comprised of server and client computing devices.
Communications within an OT network are supported by a network application protocol such as Modbus. The communication protocol gives control servers and SCADA hosts the ability to query and change the configuration of each PLC. Modbus was originally designed as a serial protocol (Modbus RTU) running over a fieldbus network but has been adapted to use Ethernet and TCP/IP as well. Other protocols include EtherNet/IP, a variant of the Common Industrial Protocol (CIP), Distributed Network Protocol (DNP3), and Siemens S7comms.