Rt Classes; Rt Classes For Profinet Io - Siemens SINAMICS S120 Function Manual

Communication PROFIBUS DP/PROFINET IO
10.3 Communications via PROFINET IO
10.3.3

RT classes

10.3.3.1

RT classes for PROFINET IO

Description
PROFINET IO is a scalable realtime communications system based on Ethernet technology.
The scalable approach is expressed with three realtime classes.
RT
The RT communication is based on standard Ethernet. The data is transferred via prioritized
Ethernet message frames.
IRTflex
This realtime class is not supported in FW 2.5 SP1.
IRTtop
In addition to the bandwidth reservation, the message frame traffic can be further optimized
by configuring the topology. This enhances the performance during data exchange and the
deterministic behavior. The IRT time interval can thus be further optimized or minimized
compared with IRTflex.
In addition to the isochronous data transfer, with IRT even the application (position control
cycle, IPO cycle) can be synchronized in the devices. This is an essential requirement for
closed-loop axis control and synchronization via the bus.
Table 10-33 Comparison between RT and IRTtop
RT class
Transfer mode
MinDeviceInterval
Isochronous application
Start time of the isochronous
application
Determinism
Reload the network configuration after
a change
Cross-traffic (controller-controller)
444
RT
Switching based on the MAC address;
prioritization of the RT message frame
possible using Ethernet-Prio (VLAN
tag)
Typically 2-8 msec
-
-
Variance of the transmission duration
by started TCP/IP message frames
-
-
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
IRTtop
Path-based switching using a topology-
based planning; no transmission of
TCP/IP frames in the IRTtop interval.
Fully deterministic, also for 250 µsec
Yes
Times for receiving the data scheduled
exactly. A synchronous application can
be started directly afterwards (similar to
DP)
Exactly planned transfer; times for
transmission and receiving are
guaranteed for any topologies.
Whenever the topology or the
communication relationships
change
Yes
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