Communication
9.4 Communication via PROFINET IO
Function Manual
Function Manual, 01/2011, 6SL3097-4AB10-0BP3
617
9.4 Communication via PROFINET IO
9.4.1 General information about PROFINET IO
9.4.1.1 Real-time (RT) and isochronous real-time (IRT) communication
Real-time communication
When communication takes place via TCP/IP, the resultant transmission times may be too
long and non-deterministic to meet production automation requirements. When
communicating time-critical IO user data, PROFINET IO therefore uses its own real-time
channel, rather than TCP/IP.
Determinism
Determinism means that a system will react in a predictable ("deterministic") manner.
With PROFINET IO, it is possible to precisely determine (predict) transmission times.
PROFINET IO with RT (Real Time)
Real time means that a system processes external events over a defined period.
Process data and alarms are always transmitted in real time (RT) within the PROFINET IO
system. RT communication provides the basis for data exchange with PROFINET IO. Real-
time data are treated as a higher priority than TCP(UDP)/IP data. Transmission of time-
critical data takes place at guaranteed time intervals.
PROFINET IO with IRT (Isochronous Real Time)
Isochronous Real Time Ethernet: Real time property of PROFINET IO where IRT telegrams
are transmitted deterministically via planned communication paths in a defined sequence to
achieve the best possible synchronism and performance between the IO controller and IO
device (drive unit). This is also known as time-scheduled communication whereby
knowledge about the network structure is utilized. IRT requires special network components
that support planned data transfer.
Cycle times of minimum 500 μs and a jitter accuracy of less than 1 μs can be achieved when
this transmission method is implemented.
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Figure 9-39 Bandwidth distribution/reservation, PROFINET IO
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