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

40-14 Industrial Communication Systems
IEC 61158 describes the redundancy concept for RT_CLASS_3 frames as “media redundancy for
planned duplication.” IEC 61784 describes the use of redundancy class 3 for RT_CLASS_3 communication
with smooth switchover of communication paths if a fault occurs. During system power-up, the IO
controller loads the data of the communication paths for both communication channels (directions) in a
communication ring to the individual nodes. Thus, it is unimportant which node fails because the loaded
“schedule” for both paths is available in the field devices. Loading of the “schedule” alone is sufficient to
exclude frames from circulating in this variant, because the destination ports are explicitly defined.
40.5 Integration of Fieldbus Systems and Web Applications
PROFINET specifies a model for integrating existing PROFIBUS and other fieldbus systems such as
INTERBUS and DeviceNet. This means that any combination of fieldbus and Ethernet-based subsystems
can be configured in a simple way. The following constrains are taken into consideration: the plant operator
would like the ability to easily integrate his existing installations into a newly installed PROFINET
system; the plant and machine manufacturer would like the ability to use the well-proven devices it is
familiar with for PROFINET automation projects, as well, without the need for any modifications; the
device manufacturer would like the ability to integrate its existing field devices into PROFINET systems
without expending any effort for modifications. Fieldbus solutions can be easily and seamlessly integrated
into a PROFINET system using proxies and gateways. Anyway, the more powerful way is using a proxy.
40.5.1 Integration via Proxy
In simplest terms, a proxy is a representative for a lower-level fieldbus system. In PROFINET, a proxy represents
a fieldbus (e.g., PROFIBUS, Interbus, Foundation Fieldbus, DeviceNet). As a result, the advantages
of fieldbuses, such as high dynamic response, pinpoint diagnostics, and automatic system configuration
without settings on devices, can be utilized in the PROFINET world. Moreover with the proxy, devices
and software tools are also supported in the accustomed manner and integrated into the handling of the
PROFINET system. The proxy coordinates the Ethernet data traffic and the fieldbus-specific data traffic.
For instance, a PROFINET/PROFIBUS proxy (on the Ethernet side) represents one or more fieldbus
devices. This proxy ensures transparent implementation of communication (no tunneling of protocols)
between networks. For example, it forwards the cyclic data coming from the Ethernet to the fieldbus
devices in a transparent manner. On the PROFIBUS DP side, the proxy works as a PROFIBUS master
that exchanges data with PROFIBUS nodes. At the same time, it is an Ethernet node with Ethernet-based
PROFINET communication.
In this process, the Ethernet communication is already defined by the available software. Only the
initialization of the process data previously provided from the lower level fieldbus to PROFINET still
has to be ensured. As a result of this concept, fieldbuses of any type can be integrated into PROFINET
with minimal effort, whereby a proxy is used to represent the lower level bus system. For instance, proxies
can be implemented as PLCs or PC-based controllers.
40.5.2 Web Integration
The PROFINET Web integration was designed mainly for commissioning and diagnostics. Possible
applications for Web integration include: testing and commissioning of the network, overview of device
data (PROFINET IO), and device diagnostics and system/device documentation. The basic component
of Web integration is the Web server. This means that even a simple PROFINET devices with Web
integration option is equipped with an “embedded Web server.” The individual functions can be implemented
depending on the performance capability of the device. This allows solutions to be customized
to each use case.
© 2011 by Taylor and Francis Group, LLC