What communication protocols are commonly used in industrial control systems?

Industrial communication protocols need to address 3 complexities - speed, cost and range. While the majority of communication in the 80's were based on Wired transfer of data - be it RS-232/3, the Modbus or CAN, lately we have seen a lot of wireless communication protocols that supplant these traditional modes. The advantage of wireless now need to be considered based on speed and data integrity. Dedicated radio chipsets dealing with FSK, LTE or QAM based coding schemes allow for greater range and less complexity in implementing connectivity- so too do Mesh networking which suits low cost NxN connections which are self routing. cost and regulatory limitations exist for RF Wireless communication.In Brief, protocol needs to be universal.

As discussed above the advantage of ethernet protocols re ease of application interfacing as the layers of the OSI are fairly advanced. GiGE and PoE have ensure that higher speeds and power needs are taken care upto 100W/10Gbps. The crucial factor here is that speeds cause network jitter/clock delay which can only be corrected in hardware. The higher layers need to decode the packets/frames and address messages to the outside world. ethernet in particlar has UDP/TCP connectivity which support both real time and connection oriented protocols. The application suitability decides whether Video, Textual or sensor data is suitable for ethernet protocols. Commodity RF/Ethernet gear enabled into LTE enabled modems also support Ethernet on chip.

Ethernet is nowadays widely used databus with different industry specific protocols, such as TRDP and other protocols in transportation industry.

ZigBee is a problematic protocol to use in OT/ICS environments. It's not the architecture as such who has redundancy & scalability in mind. Zigbee operates in the 2.4 GHz frequency spectrum, which is shared with many other devices (e.g., Wi-Fi, Bluetooth LTE, etc) and is also very prone to EMI. This can lead to interference and potential communication issues. Also not self-healing and in some problem cases rebooting the device seems the only option to get the ZigBee network up and running again.

In continuity, wireless Ethernet protocols have a PHY layer that implements connectivity over existing Mobile networks. For bespoke Industrial networks we have picocells and private networks which allow for 5G speeds to be used in house bypassing network ISP's reducing need for VPN/data security. The 3 factors here are 1) Inhouse configuration and security 2) ease of deployment 3) reduced regulatory compliance when deploying in house. For Industrial networks where high speed and longer range are needed, the advent of Starlink allows truly global scale networking. security and cost would decide if the network needs to be bespoke or can ride on regular cellphone based networks as LTE suits regular 10MBps networking covering video

OPC was an industrial standard that revolutionized the Industrial floor with quicker turnaround in terms of control and sense of shopfloor devices. The established install base of PLC would not be affected by Internet protocols unless the interface is made using open source hardware that address the bespoke nature of machine tools, robotics and Automation. However security by obfuscation is hardly an anchor to progress from. Data breaches caused by services that are part of the Application chain that address multiple applications like CoAP, MQTT offer a paradigm shift in the consumption of data. Studies need to be done to understand applicable network protocols that provide full lifecycle support for a product as Internet is evolving.

The basic need to signal presence or absence - boolean values over a serial wire is adressed by RS-232 and is universally a benchmark that solves a specific problem. However- speed, range and bandwidth dictate that other standards for Video, Textual or sensor specific data need to be multiplexed and sent. The evolution of CAN as a two wire serial protocol highlights differential signalling solves with a low voltage a fundamental issue with noise over a wired line. Specific applications where EMI/EMC or tampering are to be reduced would still need Physical serial wire protocols. The Low power always-ON sensor data which have commodity hardware also support serial protocols with ease of programming, protocol support and ability to interface.