Image Processing Reference
In-Depth Information
The adoption of Ethernet technology for industrial communication between controllers, and even
for communication with ield devices, supports direct Internet capability in the ield area, for instance,
remote user interfaces via Web browser. But, it would be unacceptable if the adoption of the Ethernet
technology would cause loss of features required in the field area, namely:
•
Time deterministic communication
•
Time-synchronized actions between field devices such as drives
•
Efficient and frequent exchange of very small data records
An implicit but essential requirement is that the office Ethernet communication capability is fully
retained so that the entire communication software involved remains usable.
This results in the following requirements:
•
Support for migration of the office Ethernet to real-time Ethernet (RTE); see below for a
definition
•
Use of standard components such as bridges, Ethernet controllers, and protocol stacks as
far as possible
To achieve the required higher quality of data transmission with limited jitter and disturbances due
to TCP/IP data traffic, it may be necessary to develop further network components. In short, the RTE
is a fieldbus specification that uses Ethernet for the lower two layers.
As a matter of fact, industrial RTE devices can neither be as cheap as in the office world (lim-
ited by the scale of industrial deployment) nor can plain Ethernet be applied to control applications
demanding some sort of hard real-time behavior; for details of the argument see []. To cope with
these limitations, many research projects proposed solutions for the introduction of quality of service,
modifications to packet processing in switches, or synchronization between devices.
he IEC/SCC
∗
committee, in addition to the maintenance of the international fieldbus and its
profile, finished a standardization project and defined additional aspects of RTE. And as in the case
of the fieldbus, there are several competing solutions and their proponents represented.
This chapter will give an outline of this new document and the requirements specified for the RTE
standardization. All solutions in this standard able to handle real-time (RT) requirements will be
presented with their key technical features.
21.2 Structure of the IEC Standardization
All industrial protocols are defined in IEC []. This document is structured according to the
open system interface (OSI) reference model in seven parts according to Table .. In parts - all
networks are identified by types. So there exist different types of networks in six different parts.
IntheIECstandard,diferentsetsofproilesarecollectedaslistedinTable..InIEC-
[] the profile sets for continuous and discrete manufacturing relative to fieldbus use in industrial
control systems are defined. Inside this first profile some version based on Ethernet technology are
also defined. In the second standard IEC - [], additional profiles for ISO/IEC - (Ether-
net) based communication networks in RT applications are defined. To identify all these profiles a
classification with communication profile families (CPF) according to Table . is introduced. Every
∗
IEC is organized in Technical Committees (TC) and Subcommittees (SC), TC deals with industrial-process mea-
surement and control and SCC with digital communication and has the scope to prepare standards on digital data
communications subsystems for industrial-process measurement and control as well as on instrumentation systems used
for research, development, and testing purposes.
