Fragmentation - Siemens SIMATIC PROFINET Function Manual

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
②
③
Figure 5-57
Note
The PROFINET IO interface of the IO controller supports fragmentation if all the ports except
one are deactivated.
PROFINET with STEP 7 V14
Function Manual, 09/2016, A5E03444486-AG
A standard Ethernet frame with TCP/IP data is up to 125 µs.
During fragmentation, the standard Ethernet frame is divided into frame segments.
The frame segments are divided into multiple short send clocks.
Fragmentation
5.6 PROFINET with performance upgrade
Functions
175