Performance Analysis of Media Redundancy Protocol

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IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, VOL. 9, NO. 1, FEBRUARY 2013
Performance Analysis of Media Redundancy Protocol (MRP)
Alessio Giorgetti, Filippo Cugini, Francesco Paolucci, Luca Valcarenghi, Member, IEEE, Alessia Pistone, and Piero Castoldi, Member, IEEE
Abstract—The International Electrotechnical Commission (IEC) recently standardized several Industrial Ethernet solutions that introduce the fieldbus concepts within Ethernet based networks. In addition, the IEC 62439 standardized a set of redundancy management protocols, including the Media Redundancy Protocol (MRP). In this way, IEC standards provide a variety of Ethernet-based solutions for satisfying both temporal and redundancy management requirements of Industrial Area Networks (IANs). In this paper, after a detailed study and implementation of MRP, two factors are identified that have an important impact on the protocol performance: the offset time and the physical detection time. A method is then provided to calculate a threshold to the network recovery time. Finally, extensive simulations and experimental measurements are performed to accurately evaluate the effect of the aforementioned factors on the protocol performance. Index Terms—IEC 62439, industrial area networks (IANs), industrial Ethernet, media redundancy protocol (MRP).
Fig. 1. Test ring network: 20 Ethernet switches.
I. INTRODUCTION URING the last decades, Ethernet imposed itself as the de-facto technology for Local Area Networks (LANs). Moreover, due to its simplicity and cost effectiveness, its utilization is currently increasing also in Metro Area Networks (MANs) and in Industrial Area Networks (IANs) [1]–[3]. However, especially in IANs, the penetration of Ethernet encountered some difficulties because of its native non deterministic behavior. Moreover, the Rapid Spanning Tree Protocol (RSTP) [4], used in traditional Ethernet networks for providing reliability against failures, does not guarantee adequate recovery times with respect to the typical grace time of industrial plants (e.g., 20 ms for time-critical automation systems) [5]–[7]. Since the beginning of the 1980s, several solutions to satisfy IANs requirements emerged in both American and European projects (e.g., TOP [8] and MAP [9]) under the general name of fieldbus. Fieldbuses have been extensively used in IANs during last decades and are still in use for a wide range of applications [10]. However, if compared with current Ethernet networks, fieldbus technologies are now obsolete especially in
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Manuscript received August 04, 2011; revised November 04, 2011; accepted January 23, 2012. Date of publication February 03, 2012; date of current version December 19, 2012. Paper no. TII-11-389. A. Giorgetti, F. Paolucci, L. Valcarenghi, and P. Castoldi are with Scuola Superiore Sant’Anna (SSSUP), 1-56124 Pisa, Italy (e-mail: a.giorgetti@sssup.it; alessio.giorgetti@sssup.it). F. Cugini is with the Consorzio Nazionale Interuniversitario per le Telecomunicazioni (CNIT), 1-56124 Pisa, Italy. A. Pistone is with the Rete Ferroviaria Italiana (RFI), Roma 00161, Italy. Color versions of one or more of the figures in this paper are available online at . Digital Object Identifier 10.1109/TII.2012.2186584
terms of throughput. Indeed, Ethernet has been continuously upgraded and 10 Gb/s interfaces are currently available at relatively low price [11]–[14]. Moreover, in the last years, the research community presented several works for improving the Ethernet performance in terms of predictability and real-time guarantees. Three main approaches have been proposed: suppressing collisions, reducing the collision probability, and deterministically solving the collisions [15]–[18]. Also, a number of network device vendors recently started to offer IANs solutions based on Ethernet interfaces, under the name of Industrial Ethernet [14], [19]–[21]. These solutions often include protocols for the automatic management of failures assuming a ring topology. The design of redundancy management protocols for providing fast traffic recovery in Ethernet-based ring networks is also a hot research topic [7], [22], [23]. Indeed, the simplicity of the ring topology allows effective and deterministic traffic recovery within typical grace times. In almost all the commercially available redundancy management protocols, one switch of the ring has the role of ring manager, while the remaining switches have the role of ring clients (Fig. 1). Each switch is connected to the ring through two ring ports. The ring manager is responsible for handling failure/recovery events. In particular, in normal working conditions, the ring manager keeps one of the two ring ports in the blocked status (i.e., the dotted link in Fig. 1) to avoid looping and guarantee the protocol functionality [4]. The failure detection can be performed with two different mechanisms. In the cyclic-polling mechanism, the ring manager monitors the ring status by continuously sending control frames on the two ring ports, and waiting for the same frames on the opposite ring port. If a certain number of control frames are lost the ring manager assumes a failure has occurred. In the failure notification mechanism, a ring client detecting a loss-of-signal communicates the failure to the ring manager. In both mechanisms, upon failure
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