Siemens SIMATIC ET 200AL, System Manual

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Functions
5.6 PROFINET with performance upgrade
PROFINET with STEP 7
210
Function Manual, 05/2021, A5E03444486-AL
5.6.2 Fragmentation
The transfer of a complete standard Ethernet frame with TCP/IP data takes up to 125 µs. This
means that the cycle time for PROFINET IO data cannot be reduced by any desired amount.
The performance upgrade uses the fragmentation procedure, which breaks down TCP/IP
frames into sub-frames. These frame segments are transferred to the target device over
multiple send clocks; there they are reassembled to the original TCP/IP frame.
Fragmentation is a requirement for cycle times lower than 250 µs. In these short send clocks,
you can use more bandwidth for cyclic IO data, since the fragments of the standard Ethernet
frames use significantly less bandwidth than a complete standard Ethernet frame.
The following figure shows how fragmentation works.
① A standard Ethernet frame with TCP/IP data is up to 125 µs.
② During fragmentation, the standard Ethernet frame is divided into frame segments.
③ The frame segments are divided into multiple short send clocks.
Figure 5-62 Fragmentation
Note
The PROFINET IO interface of the IO controller supports fragmentation if all the ports except
one are deactivated.