Siemens SCALANCE X-200 Operating Instructions Manual page 24

Network topologies / media redundancy
2.3 Media redundancy in ring topologies
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 redundancy manager no longer arrive at the other ring port, the
redundancy 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 redundancy manager are disconnected and the redundancy
clients informed of the change. The redundancy clients then use the new paths to the other
devices.
If the redundancy manager fails, the ring becomes a functional linear bus.
Media redundancy methods
The following media redundancy methods are supported by SIMATIC NET products for ring
topologies:
● HSR (High Speed Redundancy)
● MRP (Media Redundancy Protocol)
The mechanisms of these methods are similar. With both methods, up to 50 devices can
participate in the ring. HSR and MRP cannot be used in the ring at the same time.
If you configure your plant using STEP 7, you can only select MRP as the media redundancy
method.
If you configure your devices with Web Based Management, CLI or SNMP, you can choose
either HSR or MRP.
Media redundancy with IRT
For ring topologies in which MRP is activated, the "MRPD" function is activated automatically
for IRT devices capable of IRT, if this is supported by the device.
● MRPD (Media Redundancy with Path Duplication)
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Reconfiguration time: 0.3 seconds
Reconfiguration time: 0.2 seconds
Automatic configuration of the ring
For use only with SCALANCE X-200IRT
This procedure allows redundancy with IRT. You will find details in the section MRPD
(Page 27).
Operating Instructions, 12/2011, A5E00349864-19
SCALANCE X-200