Image Processing Reference
In-Depth Information
Operator
workstation
Trend server
Backbone
Router
Router
Router
Zone 1
Zone 2
Segment 3:
machine room
Segment 2: floor 2
(seminar rooms)
Segment 1: floor 1
(offices)
FIGURE .
Automation network and backbone.
Even if this has become commercial reality today, requirements at the top and bottom of the
pyramidremaindiverse.Inparticular,thisconcernsthroughputandeaseofinstallation.
Therefore, a two-tier architecture has become popular where
fieldbus segments
are interconnected
by a high-performance network
backbone
(Figure .). While they can share most of the protocol
stack, different communication media are deployed for cost efficiency.
A typical building network infrastructure consists of independent fieldbus segments for each floor,
which connect sensors and actuators at the room level. he backbone channel that connects them may
also span building complexes. Plant networks may use a separate controller network, although DDC
stations will often connect to the backbone directly.
The data rate of the fieldbus segments remains geared towards the requirements of process data
exchange. Although especially during configuration and commissioning (program download) large
amounts of data need to be transferred, this occurs seldom compared to regular operation. Moreover,
it is not time critical. herefore, longer transfer times are acceptable.
As a parallel trend, strongly domain specific busses are emerging. In contrast to those protocols
which are built around the concept of using a single protocol throughout the system, these protocols
are not intended for multiple application domains. They replace the interfaces that were (and are)
traditionally used to connect field devices to controllers (voltage-free contacts, - V, Pt …).
They basically contain services to access a mix of I/O functions, together with highly application-
specific processing functions. Their application layer design does not suggest significant relocation
of automation functions into field devices. Therefore, these busses can only be used together with
domain-specific controllers, gateways, or (future) DDC stations equipped with appropriate inter-
faces. In return, focusing on a particular application domain and a minimum set of functions
allows additional functionality (such as “Plug and Play”) to be realized, while keeping resource
requirements low.
