A reliable & efficient communications network

Development of the first Programmable Logic Controllers (PLCs) was driven by the needs of the automotive industry in late ‘60s with the Modicon 084 being credited as the first device to market. Communication between PLCs was initially via serial interfaces and solutions were proprietary with each major vendor’s equipment communicating via a custom bus protocol.  For simple systems with no plans to expand or connect to other components, proprietary communication remains a valid option. However, as the need arose to deploy equipment from multiple vendors, a number of standard communication protocols were developed which came to be adopted, based on the specifics of the application – e.g. sensor type, controller type and physical environment. Due to the high capital costs involved in industrial plant and machinery, and the correspondingly long lifecycles, many of these serial-based protocols are still popular today and indeed still have their place, allowing quick and easy connections between a single supplier’s products.

Examples of these legacy protocols include PROFIBUS, CAN bus, Modbus and CC-Link, all of which are still found in the modern factory. Factory systems tend to be hierarchically classified as shown in figure 1, with devices falling into one of 5 levels. The above protocols tend to be classified as “Fieldbus” protocols, signifying that they have been developed to enable “field devices” such as sensors, motors, actuators, etc. to communicate with PLCs.

Fig 1: Industrial Communications Hierarchy. Source: The Industrial Communications Systems, PROFIBUS and PROFInet, Igor Belai, Peter Drahos

Ethernet/Industry 4.0 trends

The continuing drive to improve productivity and return on assets has seen a growth in the levels of factory automation and a proliferation of connected devices. The production lines of the Industry 4.0, “smart factory”, are becoming more diverse, requiring interoperability of a larger range of devices, including cyber-physical systems, from different manufacturers, driving the need for and development of open systems and common standards. Parallels can be seen here with developments in the telecoms industry where innovation was fuelled by open standards, enabling solution providers to build services on platforms comprising equipment from multiple vendors. The lower costs of these platforms reduced barriers to entry, enabling entrepreneurial service models and further new services.

The growth in adoption of Ethernet as an industrial communications protocol has played a key role in the evolution of the smart factory. Although it has many advantages, Ethernet deployment was initially restricted to the control and information levels of the industrial communications hierarchy, owing to the deterministic nature of many industrial processes. To overcome this limitation, a number of major Industrial OEMs developed extensions to the standard Ethernet protocol, such as PROFINET, Ethernet/IP, EtherCAT, ModbusTCP and several others. (These extensions modified the Data Link, Network and/or Transport Layers.) These extensions have since become "open standards" and are widely deployed within the industry, enabling the deterministic issues to be overcome to some extent. There are two major issues with these protocols however:

- Not being fully compatible with Ethernet the various real-time protocols can’t exist on the same Ethernet network, and

- Specific hardware interfaces are required inside any connected devices

To address this, the Institute of Electrical and Electronics Engineers (IEEE) has recently announced a set of IEEE 802 Ethernet sub-standards which have added the mechanisms required to support real-time communication. These sub-standards include time-controlled transmission, synchronization, and bandwidth reservation and will enable all data – including real-time information – to be transmitted through a single network simultaneously.

The above developments will enable Ethernet to accelerate its penetration of the process and field bus levels of the industrial communications hierarchy. A recent report by HMS Industrial Networks, claims that, in 2017, Industrial Ethernet accounted for 52% of new installed nodes with fieldbuses at 42%. EtherNet/IP is now the most widely installed network at 15%, followed by PROFINET and PROFIBUS, both at 12% The relevant shares of the most popular protocols by new installs is shown below.

Navigating the options

As discussed above, a number of different protocols exist in today’s factory, some legacy and others developed to take advantage of Ethernet capabilities, whilst addressing the Deterministic or Time Sensitive nature of many industrial processes.

Industry 4.0 has been termed as the fourth industrial revolution in which industrial automation in the smart factory is expected to strongly drive future economic growth. A reliable and efficient communications network, connecting all the components of the factory together, is a key enabler of Industry 4.0. Whilst legacy networks and protocols still have a role to play, the rising popularity of industrial Ethernet will see many of these upgraded as equipment is replaced.

The use of Ethernet throughout the communications hierarchy promises to simplify the transfer of information from the factory floor or field level to the corporate ERP systems. This level of integration will underpin a transformation of many of today’s business processes with a consequent impact on productivity and profitability.
Many different industrial Ethernet protocols have been implemented in the field, each with its own pros and cons. Recent work completed by the IEEE to extend the 802.3 Ethernet standards should enable convergence of industrial Ethernet protocols will to deliver hard real-time, deterministic communication links with better reliability and integrated safety.