Citation: Smołka, I.; Stój, J.
Utilization of SDN Technology for
Flexible EtherCAT Networks
Applications. Sensors 2022, 22, 1944.
https://doi.org/10.3390/s22051944
Academic Editor: Xiaochun Cheng
Received: 30 November 2021
Accepted: 28 February 2022
Published: 2 March 2022
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Article
Utilization of SDN Technology for Flexible EtherCAT
Networks Applications
Ireneusz Smołka * and Jacek Stój
Department of Distributed Systems and Informatic Devices, Faculty of Automatic Control, Electronics and
Computer Science, Silesian University of Technology, 44-100 Gliwice, Poland; jacek.stoj@polsl.pl
* Correspondence: ireneusz.smolka@polsl.pl
Abstract:
At the beginning of the current century, Ethernet-based communication networks began to
be implemented in industrial applications. Some previously used protocols were migrated to Ethernet
networks, while many others were strictly developed for this communication medium. Numerous
industrial Ethernet protocols do not deliver all the capabilities provided by the Ethernet. For example,
limitations may arise associated with wireless communication, use of dedicated switching devices,
or operation solely for certain topologies. On the other hand, new technologies are now available,
such as software defined networks (SDN), that add new features to Ethernet-based communication
systems. In this paper, an EtherCAT network in combination with SDN is analyzed. EtherCAT
network may only consist of devices with an implemented EtherCAT protocol stack. Therefore,
regular Ethernet switches cannot typically be used in this network and, hence, special network
infrastructure may be required to create topologies other than standard line topology. It is shown,
however, that this limitation can be overcome by the application of SDN. In addition, a definition
of datagram forwarding rules (called SDN flows here) is given, and we demonstrate that EtherCAT
datagrams can be sent through routes that are required for proper EtherCAT network operation.
Keywords:
software defined networks; networked control systems; real-time; industrial ethernet;
EtherCAT; OpenFlow; OpenWRT
1. Introduction
Efficient communication systems for industry are indispensable nowadays. New
industrial systems are most often distributed, and they consist of many devices connected
by networks. For many years, data exchange between nodes in industrial communication
systems was based on fieldbuses. However, in the early 2000s, an Ethernet standard
began to be extensively implemented for this purpose. Many protocols used for fieldbuses
migrated to, after some adaptations, modern Ethernet communication links, e.g., Modbus
TCP [
1
]. In addition, other protocols were developed strictly for the Ethernet, these include:
•
Ethernet Powerlink EPL, introduced by the company B&R (Eggelsberg, Austria)
in 2001.
•
Ethernet/IP managed by ODVA (Open DeviceNet Vendors Association), launched
in 2000.
• Profinet and EtherCAT, both presented for the first time at Hannover Fair in 2003.
Soon afterwards these protocols, alongside some others, became part of the interna-
tional standard IEC 61158/IEC 61784-2 [
2
] and, today, they are among the most recognizable
in the domain of industrial automation. It is noteworthy that another important protocol,
which is not defined in this standard, is known as OPC UA; its first version was released in
2006 [3,4].
Even though numerous protocols were developed solely for application as an Ethernet
standard, they cannot take advantage of all the characteristic features of an Ethernet
network. The limitations start from the temporal requirements, typical in industrial systems
Sensors 2022, 22, 1944. https://doi.org/10.3390/s22051944 https://www.mdpi.com/journal/sensors
