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SERBIAN JOURNAL OF ELECTRICAL ENGINEERING
Vol. 9, No. 1, February 2012, 33-42
UDK: 004.732

DOI: 10.2298/SJEE1201033K

Performance Evaluation of the Switched
EtherCAT Networks with VLAN Tagging*
Mladen Knežić1, Branko Dokić1, Željko Ivanović1
Abstract: EtherCAT technology is one of the most popular Real-Time Ethernet (RTE) solutions present on the market at this time. Due to its communication efficiency, EtherCAT is particularly suitable for networks with a large number of devices which demand short cycle times. This paper reviews the application aspects and implementation issues of the Switched EtherCAT networks with VLAN tagging, including their limitations, and provides guidelines for engineering staff in selection of the optimal solution when designing a specific automation system.

Keywords: Cycle time, Performance analysis, Real-Time Ethernet, Switched EtherCAT, Topology, VLAN tagging.

1

Introduction

Modern factories have hundreds of distributed field devices (sensors and actuators) that communicate with each other. One of the major roles of today’s automation systems is to provide efficient communication mechanisms between devices distributed in the field. It is expected that Real-Time Ethernet (RTE) will replace the old fieldbus systems in the near future. In addition of being one of the most popular RTE solutions on the market, EtherCAT protocol offers high communication efficiency irrespective of used topology. Also, it provides the high level of flexibility along with automated and easy network configuration.

EtherCAT is particularly suitable for the networks with large number of I/O devices distributed in the plant, which demand short cycle times. In [1] and [2], it was shown that the most efficient communication in EtherCAT can be achieved using ring topology. As a criterion, the minimum communication cycle time performance indicator defined in [3] was used. The ring topology in EtherCAT is basically linear topology connected in cable redundancy mode of operation. On the other side, the most favorable topology in automation systems is line topology [4, 5].

1

University of Banja Luka, Faculty of Electrical Engineering, Patre 5, 78000 Banja Luka, Bosnia and Herzegovina; E-mails: [email protected]; [email protected]; [email protected] *Award for the best paper presented in Section Electronics, at Conference ETRAN 2011, June 6 – 9, Banja Vrućica – Teslić, Bosnia and Herzegovina.

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M. Knežić, B. Dokić, Ž. Ivanović

Although EtherCAT technology provides short cycle times for networks with large number of devices, its performance can become critical parameter in case of huge networks that connects devices from different departments of production in the factory. For applications that require very short communication cycle times, implementation of the desired system with line (or even ring topology) may become questionable. In such cases, different approaches must be used.

This paper describes the approaches that are commonly used to improve communication efficiency of the EtherCAT networks with large number of devices. Special attention is paid to the Switched EtherCAT approach with VLAN tagging whose performance potential is thoroughly elaborated. In Section 2, the basics of the EtherCAT protocol are outlined. Section 3 introduces the concepts of the Switched EtherCAT technology. In Section 4, performances of the Switched EtherCAT approach with VLAN tagging are evaluated for a number of scenarios. Section 5 presents the simulation results. Finally, Section 6 discusses some of the main conclusions and provides guidelines in selection of the optimal solution when desig...

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