Maintworld 1/2017

INDUSTRIAL COMMUNICATION
IT protocols via a common medium in
addition to fast real-time data transmission.
In addition, users and manufacturers
benefit from the use of standardized
Ethernet hardware, such as passive and
active infrastructure components.
However, a uniform standard remains
a dream: There is a large number
of competing communication
solutions and although they all use the
widespread Ethernet technology, they
specify different protocols and profiles
in the superimposed ISO/OSI layers.
Thus, devices that support different
Industrial Ethernet standards are not
compatible or interoperable with each
other. Moreover, most devices that
support different real-time Ethernet
protocols cannot coexist in a common
network, thereby losing the advantages
of a common network standard. Most
real-time Ethernet solutions use the
network on an exclusive basis, meaning
that only devices of one’s “own” protocol
can be operated on the network. Devices
that support other real-time Ethernet
protocols, as well as standard Ethernet
protocols, can be connected only via
gateways or special switches. Other
protocols can only be transmitted over
the network by tunnelling them over the
underlying real-time protocol, which
can significantly harm the functioning
and performance of a system. The future
Ethernet IEEE 802.1 TSN (Time Sensitive
Networks) standard will eventually
make time-controlled transmission of
real-time critical messages via standard
Ethernet components possible. Most
likely, this Ethernet TSN technology will
have a significant impact on improving
the heterogeneous landscape of realtime
Ethernet dialects.
Important Role of OPC UA
OPC UA plays a very important role in
advancing the convergence of IT and automation
technology, thus enabling the
consistent exchange of information from
the corporate level down to the control
or field level. From a technical perspective,
OPC UA is characterized by the fact
that it contains both, mechanisms for
data exchange and an information model
which allows the structure and semantics
of the information exchanged to be
defined. This technology can not only be
integrated into devices on any platform
with various programming languages,
but systems of any degree of complexity
can be fully described with it. In addition,
the OPC UA technology is standardized
on an international basis and has
very wide acceptance from manufacturers
and users worldwide.
However, although OPC UA is in fact
a communication standard that extends
from the enterprise level down to the
control & field level, it has two key limitations.
One is that OPC UA can use or
replace existing fieldbus and Industrial
Ethernet systems only where there are
no specialized and sophisticated timeand
deterministic-communication
requirements. The other limitation is
that OPC UA only defines how data are
described and exchanged. The actual
meaning of the data, which is generally
understood and defined as semantics, is
not defined.
A very promising approach is therefore
to combine and map the existing
real-time Ethernet protocols and the
respective profiles with OPC UA. In doing
so, process and device data are made
available not just locally via the respective
real-time network but also via any
superordinate network infrastructure,
e.g. the Internet or Intranet, via OPC
UA, in a uniform and cross-manufacturer
manner. Thus, not only is data exchange
between the machine periphery
and superordinate IT systems simplified,
but the requirements of Industry
OPC UA PLAYS A VERY IMPORTANT ROLE IN ADVANCING THE
CONVERGENCE OF IT AND AUTOMATION TECHNOLOGY.
4.0 with respect to semantic interoperability
are also supported.
In this scenario, real-time capabilities
of OPC UA are not required, as the
real-time performance is guaranteed
by the respective underlying real-time
network. Of course, application scenarios
are possible in which a real-time
capability of OPC UA is necessary,
for example in machine-to-machine
communication or in the linking of
process-related machine periphery via
OPC UA. For this, the so-called OPC UA
publisher-subscriber protocol extension
in combination with the future Ethernet
TSN standard is positioned.
In order to apply OPC UA in a consistent
way down to the field level, without
affecting the performance and realtime
characteristic of the underlying real-time
network, the real-time networks
need to be capable of supporting the
multi-protocol capability, meaning that
real-time protocols and IP based protocols
can coexist and at the same time can
run independent of each other.
If these requirements are fulfilled,
today’s bus systems in combination with
technologies such as OPC UA and Ethernet
TSN can make a significant contribution
to the further convergence of
information and automation technologies.
Let’s make it happen.
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