wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

39
Ethernet POWERLINK
Paulo Pedreiras
University of Aveiro
Stefan Schoenegger
B&R Industrial Automation
Lucia Seno
Italian National
Research Council
Stefano Vitturi
Italian National
Research Council
39.1 Introduction..................................................................................... 39-1
39.2 EPL Protocol..................................................................................... 39-1
39.3 Frame Mapping...............................................................................39-3
39.4 Network Configurations................................................................39-4
39.5 Redundancy Aspects.......................................................................39-5
Medium Redundancy. •. MN Redundancy
39.6 Security Aspects.............................................................................. 39-7
POWERLINK Safety
39.7 Performance Analysis.....................................................................39-8
Jitter. •. Turn-Around Time. •. Cycle Time. •. Acyclic Traffic
References.................................................................................................. 39-10
39.1 Introduction
Ethernet POWERLINK (EPL) is a real-time Ethernet (RTE) network originally developed by B&R
GmbH [1] and currently managed by the Ethernet POWERLINK Standardization Group (EPSG) [2].
The first version of EPL was developed by B&R in 2001 and subsequently published as an open standard,
namely version 2.0 [11], by the EPSG in 2003. Such a version has been then encompassed in the IEC 61784
International Standard [7] where it is referred as Communication Profile (CP) #1 of the Communication
Profile Family (CPF) #13. A more recent version of the EPL specification [6] is currently downloadable
from the EPSG Web site. Starting from the tight timing requirements of industrial communication
systems [15], the EPL protocol has been developed in order to provide very fast communication cycles
(down to 100.μs) with low jitter (below 1.μs) and, at the same time, maintaining compatibility with
legacy Ethernet. An application layer protocol has been introduced on top of the EPL communication
stack. In particular, the well-established CANOpen standard [10] has been chosen, ensuring in such a
way compatibility with a wide number of already deployed communication systems. In this context,
EPL is often referred as “CANOpen over Ethernet.”
39.2 EPL Protocol
The communication architecture of EPL is shown in Figure 39.1.
As can be seen, EPL makes use of the native Ethernet stack and, in particular, it is defined as a data-link
layer (EPL DLL) protocol, placed on top of the Ethernet medium access control (MAC) [8] that, as it is well
known, relies on a CSMA/CD (carrier sense multiple access with collision detection) technique. The physical
layer of the EPL is the same as that of the Ethernet. Specifically, the 100BASE-X half-duplex transmission
mode has been chosen. Moreover, both RJ-45 and M12 connectors can be used at the user’s discretion. The
EPL specification also recommends the use of standard patch cables (twisted pair, screened twisted pair,
AWG26). Finally, concerning installation guidelines, EPL follows the recommendations of IAONA [5].
39-1
© 2011 by Taylor and Francis Group, LLC