Image Processing Reference
In-Depth Information
expect completely new automation networks optimized for wireless communication, where maybe
only the application layer protocol remains compatible with traditional wired solutions to achieve
integration.
Driven by ever more demanding application areas, communication networks for safety-relevant
systems gain importance. In special fields such as x-by-wire for vehicles and avionics, dedicated field-
bus systems were developed that specifically addressed the problem of reliable communication [].
Examples are TTP, FlexRay, byteflight, or ARINC . These networks are relatively new and can
build on substantial experience of the scientific community as well as industry with other fieldbus
systems. As this domain is subject to very stringent normative regulations and thus very conservative,
it was dominated for a long time (and still is) by point-to-point connections between devices. The
first “older” fieldbus system to penetrate this field was the CAN-based Safety Bus []. It took a long
time and effort for this system to pass the costly certification procedures. Nevertheless, it was finally
accepted also by the users, which was by no means obvious in an area concerned with the protection
of human life, given that computer networks usually have the psychological disadvantage of being
considered unreliable. After this pioneering work, other approaches like the ProfiSafe profile [],
INTERBUS Safety [], AS-i Safety [], and recently also Ethernet/IPsafety [], WorldFIP [],
and SafetyLON (still under development at the time of writing) readily followed. All these traditional
fieldbus systems that were originally not designed for safety-critical applications implement this par-
ticular functionality by means of dedicated profiles. In practice, they wrap additional safety protocols
into the normal payload data which foresee a set of measures to make communication more reliable:
sequence numbers, additional CRCs and confirmations, timestamps, heartbeat functions and time-
outs together with safety monitors and built-in test functions for the hardware components detect
residual errors and may typically achieve safety integrity level according to IEC , which makes
them applicable for fire emergencies, alarming, traffic and transportation applications, or power plant
control.
Apart from communication protocol issues, there are two major trends to be noticed. One is
the growing complexity of networks and networked systems in general. This is manifested by the
increasing integration of fieldbus systems in higher-level, heterogeneous networks, and process con-
trol systems on the one hand and the massive use of Internet technologies to achieve simplification
and possible harmonization of existing solutions. his in fact drastically reduces the number of layers
in the traditional network hierarchy, which only reflects the trend toward peer-to-peer networking on
a protocol level. he other trend is the still increasing capabilities of embedded devices, the possibil-
ity to integrate more computational resources while at the same time reducing energy consumption.
Systems on Chip with on-chip memory, network interfaces, and the computing power of a complete
industrial PC offer sufficient resources for smart and low-cost sensors and actuators. his evolution
is on the one hand the foundation of the current boom of Ethernet in automation. On the other, it
will stimulate more research in the already booming field of sensor networks []. What is likely to
be seen in the future are much more ubiquitous Ethernet- and Internet-based concepts, probably
optimized to meet special performance requirements on the field level but still compatible with the
standards in the management area. At any rate, these concepts and protocols will have to be scalable
to allow for seamless integration of low-level, highly specialized sensor/actuator networks tailored
meeting the demands of low power consumption, small-footprint implementation, high flexibility,
andself-organization.heieldbusofthefuturewillbeaveryversatilething:embeddednetworkand
a network of embedded systems alike.
20.9 Appendix
The tables presented here give an overview of selected fieldbus systems, categorized by application
domain (Tables . through .). .).The list is necessarily incomplete, although care has been taken to
