Technical data

Communication
9.4 Communication via PROFINET IO
Function Manual
Function Manual, 06/2012, 6SL3097-4AB10-0BP4
663
IRT "high performance"
In addition to the bandwidth reservation, the telegram 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 with
respect to IRT "high flexibility".
In addition to the isochronous data transfer provided by IRT, even the application itself
(position control cycle, IPO cycle) can be isochronous in the devices. This is an essential
requirement for closed-loop axis control and synchronization via the bus. Isochronous data
transfer with cycle times well below one millisecond and with a deviation in the cycle start
(jitter) of less than a microsecond provide sufficient performance reserves for demanding
motion control applications.
The RT classes IRT "high flexibility" and IRT "high performance" can be selected as options
in the synchronization settings configuration area of HW Config. In the description below,
both these classes are simply referred to as "IRT".
In contrast to standard Ethernet and PROFINET IO with RT, the telegrams for PROFINET IO
with IRT are transmitted according to a schedule.
Comparison between RT and IRT
Table 9- 39 Comparison between RT and IRT
RT class RT IRT "high flexibility" IRT "high performance"
Transfer mode Switching based on the MAC
address; prioritization of the
RT telegrams possible using
Ethernet-Prio (VLAN tag)
Switching using the MAC
address;
bandwidth reservation by
reserving an IRT "high
flexibility" interval in which
only IRT "high flexibility"
frames are transferred but,
for example, no TCP/IP
frames
Path-based switching
according to a topology-
based plan; no transmission
of TCP/IP frames and IRT
"high flexibility" frames in the
IRT "high performance"
interval.
Isochronous application
in the IO controller
No No Yes
Determinism Variance of the transmission
duration by started TCP/IP
telegrams
Guaranteed transmission of
the IRT "high flexibility"
telegrams in the current
cycle by the reserved
bandwidth.
Exactly planned transfer;
times for transmission and
receiving are guaranteed for
any topologies.
Reload the network
configuration after a change
Not relevant Only when the size of the
IRT "high flexibility" interval
needs to be modified
(reservation of position is
possible)
Whenever the topology or
the communication
relationships
change
Maximum switching depth
(number of switches in one
line)
10 at 1 ms 61 32
For possible send cycles, see subitem "Send cycles and update cycles for RT classes" in table "Adjustable send cycles
and update cycles"