Communication
11.2 PROFINET
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
955
How media redundancy works in a ring topology
The data paths between the individual devices are automatically reconfigured if the ring is
interrupted at any point. The devices are available again after reconfiguration.
In the MRP manager, one of the two ring ports is blocked in uninterrupted network operation
for normal communication so that no data frames are circulated. In terms of data
transmission, the ring topology is a linear bus topology. The MRP manager monitors the ring
for interruptions. It does this by sending test frames both from ring port 1 and ring port 2. The
test frames run round the ring in both directions until they arrive at the other ring port of the
MRP manager.
An interruption of the ring can be caused by loss of the connection between two devices or
by failure of a device in the ring.
If the test frames of the MRP manager no longer arrive at the other ring port during an
interruption of the ring, the MRP manager connects its two ring ports. This substitute path
once again restores a functioning connection between all remaining devices in the form of a
linear bus topology.
The time between the ring interruption and restoration of a functional linear topology is
known as the reconfiguration time.
As soon as the interruption is eliminated, the original transmission paths are established
again, the two ring ports of the MRP manager are disconnected, and the MRP clients
informed of the change. The MRP clients then use the original paths again to the other
devices.
The standard method of media redundancy in SIMATIC is Media Redundancy Protocol
(MRP) with a typical reconfiguration time of 200 ms. Up to 50 devices can participate per
ring.
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