The Rise of the Industrial Internet of Things

The industrial internet of things (IIoT) is continually growing as companies realize how connecting the machines and resources involved in their manufacturing process can improve their profitability. What is IIoT? In a nutshell, IIoT involves capturing sensor data and sending it via machine-to-machine (M2M) communication to the cloud where big data technology takes over to analyze and interpret the data. Using this data, companies can find and correct inefficiencies and potential malfunctions, all while supporting business intelligence and saving time and money.

In order for machine data to get to the cloud, some sort of communication has to be set up. In the past, several serial-based protocols were used for M2M communications including PROFIBUS®, CAN bus, Modbus®, and CC-Link®. All of these are still being used today.

PROFIBUS is currently deployed in industrial automation systems. This protocol provides communication for process and auxiliary data at up to 12 Mbps while supporting up to 126 addresses.

CAN bus, originally developed for the automotive industry, is another fieldbus technology used for industrial automation. Serial communication speeds up to 1 Mbps are supported by this protocol. There are two higher level protocols, CANopen® and DeviceNet, that are standardized on top of CAN bus. These two higher level protocols allow interoperability with devices on the same industrial network. CANopen supports 127 network nodes while DeviceNet supports 64 network nodes.

Modbus is a simple open-source protocol that can connect up to 247 nodes. It has transmission speeds up to 115 Kbps and is easily implemented on RS-232 or RS-485 links.

CC-Link, originally developed by Mitsubishi, is popular in Japan and Asia as an industrial network protocol. This protocol is RS-485 based with the capability of connecting up to 64 network nodes at up to 10 Mbps.

The Future is Gravitating towards Ethernet Solutions

Many IIoT networks are now moving towards Ethernet-based solutions. One of the advantages of Ethernet is that it is flexible with both network topology and number of system nodes. There have arisen several industrial Ethernet protocols that are being used today including EtherCAT, EtherNet/IP, PROFINET, POWERLINK, Sercos III, CC-Link IE, and Modbus/TCP.

EtherCAT enables packets to be processed on-the-fly for real-time automation applications. This is a MAC-layer protocol that is optimized for process data and uses standard IEEE 802.3 Ethernet frames. EtherCAT connects up to 65,535 system nodes.

EtherNet/IP is an application-layer protocol which uses Common Industrial Protocol (CIP) over TCP/IP. CIP is capable of being used in multiple physical media such as CAN bus (DeviceNet), a dedicated network (ControlNet), and over Ethernet (EtherNet/IP). EtherNet/IP can have an unlimited number of system nodes since it uses standard Ethernet and switches. Although it is compatible with many standard internet and Ethernet protocols, it has limited real-time and deterministic capabilities.

PROFINET, widely used by major industrial equipment manufacturers in their industrial Ethernet, has three different classes.

  • PROFINET Class A uses remote procedure calling on TCP/IP to bridge the Ethernet and PROFIBUS, providing proxy access to PROFIBUS. It is mostly used for parameter data and cyclic I/O and has a cycle time of around 100 ms. PROFINET Class A is typically used for infrastructure and building automation.
  • PROFINET Class B has a cycle time of around 10 ms and introduces a software-based real-time component. Class B is also referred to as PROFINET Real-Time (PROFINET RT). This protocol can be used in PLC-type applications. It is typically used in factory and process automation.
  • PROFINET Class C requires special hardware to be able to reduce the cycle time to less than 1 ms, enabling it to sufficiently deliver real-time performance for motion control operations. Class C is also called PROFINET IRT as it is isochronous and real-time.

The common topologies for PROFINET are Branch and Star. To be able to realize the required system performance, care in topology planning is a must.

POWERLINK allows free selection of network topology as it runs on top of IEEE 802.3. This protocol uses a polling and time slicing technique to allow for real-time data exchange. It is suitable for many automation systems from PLC-to-PLC communication to motion and I/O control.

Sercos III, the third generation of the Serial Real-time Communication System (Sercos) protocol, combines real-time Ethernet enabled by on-the-fly packet processing and low latency industrial Ethernet enabled by TCP/IP communication. It has cycle times as low as 31.25 µs putting it on par with EtherCAT and PROFINET IRT. Sercos III supports using ring or line topologies and can have up to 511 network slave nodes. This protocol is mainly used in servo drive controls.

CC-Link IE, or CC-Link Industrial Ethernet, has two versions: CC-Link IE Control and CC-Link Field.

  • CC-Link IE Control, developed for controller-to-controller interfaces, can have up to 120 network nodes.
  • CC-Link IE Field, developed for motion control and I/O communications, can have up to 254 network nodes.

CC-Link IE only supports a ring topology, without switches, providing network redundancy. However, there are a limited number of nodes that can be supported and the cycle time varies with the number of nodes in the network.

Modbus/TCP is an extension of Modbus. This protocol enables Modbus messaging over TCP/IP on top of Ethernet. While being simple to implement on a standard Ethernet network, real-time and deterministic communications are not guaranteed.


There are still several serial-based legacy communications protocols still in use for industrial communications today. However, as the IIoT is evolving, industrial Ethernet-based solutions are taking over. Industrial Ethernet solutions generally provide better real-time and deterministic communications that are highly reliable and can handle more network nodes than serial-based systems.

About this author

Image of Rich Miron, Digi-Key Electronics

Rich Miron, Sr. Technical Content Developer at Digi-Key Electronics, has been in the Technical Content group since 2007 with primary responsibility for writing and editing articles, blogs and Product Training Modules. Prior to Digi-Key, he tested and qualified instrumentation and control systems for nuclear submarines. Rich holds a degree in electrical and electronics engineering from North Dakota State University in Fargo, ND.

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