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

40-4 Industrial Communication Systems
has been designed for performance, brings with it specific hardware requirements (Ethernet controller/
switch with support of isochronous operation).
RT_CLASS_3: Synchronized communication within a subnet. During synchronized RT_CLASS_3
communication, process data are transmitted with maximum precision in an exact order specified during
system engineering (maximum allowable deviation from start of bus cycle of 1.μs). With the aid of
topology-optimized data transmission, this is also referred to as IRT functionality. In RT_CLASS_3
communication, there are no wait times. In order to take advantage of the data transmission designed
for maximum performance, special hardware requirements apply (Ethernet controller with support of
isochronous operation).
RT_CLASS_UDP: The unsynchronized cross-subnet communication between different subnets requires
addressing information via the destination network (IP address). This variant is also referred to as RT_
CLASS_UDP. Standard switches can be used in this RT class.
For RT frames, data cycles of 5.ms at 100.Mbps in full-duplex mode with VLAN tag are sufficient. This
RT communication can be realized with all available standard network components.
40.1.3 Conformance Classes
Since the complete scope of functions implemented in PROFINET IO is not required in every automation
system, the conformance classes/application classes are introduced. The objective is to simplify the
application areas of PROFINET IO. The resulting application classes enable plant operators to easily
select field devices and bus components with explicitly defined minimum properties. The minimum
requirements for three conformance classes (CC-A, CC-B, CC-C) have been defined from the perspective
of the plant operator. In addition to the three application classes, additional specifications have been
made for device types, type of communication, transmission medium used, and redundancy behavior.
This specification ensures the interoperability in an automation system with regard to the scope of functions
and performance parameters. It is assured that all field devices within the selected CC meet the
same minimum requirements. The application areas currently are
CC-A: Use of the infrastructure of an existing Ethernet network including integration of basic
PROFINET functionality. All IT services can be used without restrictions. Examples of typical
applications are in building automation and process automation. Wireless communication is
only possible in this class.
CC-B: In addition to the functions of CC-A, the scope of functions of CC-B supports easy and
user-friendly device replacement without the need for an engineering tool. To increase the data
security, a media redundancy protocol for TCP (UDP)/IP data is integrated. Examples of typical
applications are in automation systems with a higher-level machine controller that place
relatively low demands for a deterministic data cycle.
CC-C: In addition to the functions of CC-B, the scope of functions of CC-C supports highprecision
and deterministic data transmission, including for isochronous applications. The
integrated media redundancy enables smooth switchover of the I/O data traffic if a fault
occurs. An example of a typical application is the field of motion control.
40.1.4 Prerequisites
PROFINET IO field devices are addressed using MAC addresses and IP addresses. Each subnet is represented
by a different network_ID (subnet mask). PROFINET IO field devices are always connected
as network components via switches. This takes the form of a star topology with separate multiport
© 2011 by Taylor and Francis Group, LLC