Siemens SIMATIC ET 200AL, System Manual

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Functions
5.6 PROFINET with performance upgrade
PROFINET with STEP 7
Function Manual, 05/2021, A5E03444486-AL
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5.6.3 Fast forwarding
To be able to decide whether a frame should be forwarded or used, a PROFINET IO device
requires the frame ID. It previously took 1440 ns until the frame ID was present in the
IO device.
The performance upgrade uses the fast forwarding procedure in which the frame ID is located
nearer the front of the frame. The throughput time in the device is reduced to 320 ns.
With fast forwarding, the throughput time of the frame is reduced in your PROFINET IO
system. This results in decisive performance advantages, particularly in line, ring and tree
topologies.
The figure below compares the throughput of a PROFINET IO frame in an IO device with and
without fast forwarding.
① Start:
•
Both PROFINET frames reach the IO device.
The IO devices start to check the frames for the frame ID
② After 320 ns:
•
Without fast forwarding: The IO device is still checking the PROFINET frame for the frame ID.
• With fast forwarding: The IO device receives the frame ID from the PROFINET frame and
forwards the frame.
③ After 1440 ns:
•
Without fast forwarding: The IO device receives the frame ID from the PROFINET frame and
forwards the frame.
• The PROFINET frame with fast forwarding is "ahead" of the PROFINET frame without fast
forwarding.
Figure 5-63 Fast forwarding