Siemens Industrial Ethernet Switches SCALANCE X-200 - Manual (Page 23)

Network topologies / media redundancy
2.3 Media redundancy in ring topologies
SCALANCE X-200
Operating Instructions, 12/2011, A5E00349864-19
23
2.3 Media redundancy in ring topologies
Structure of a ring topology
Nodes in a ring topology can be external switches and/or the integrated switches of
communications modules.
To set up a ring topology with media redundancy, you bring together the two free ends of a
linear bus topology in one device. Closing the linear bus topology to form a ring is achieved
with two ports (ring ports) of a device in the ring. This device is the redundancy manager. All
other devices in the ring are redundancy clients.
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Figure 2-8 Devices in a ring topology with media redundancy
The two ring ports of a device are the ports that establish the connection to its two
neighboring devices in the ring topology. The ring ports are selected and set in the
configuration of the relevant device. On the S7 Ethernet CP modules, the ring ports are
indicated by an "R" after the port number.
Note
Create the configuration of the devices to be connected to form a ring before you close the
ring.
How media redundancy works in a ring topology
When using media redundancy, the data paths between the individual devices are
reconfigured if the ring is interrupted at one point. Following reconfiguration of the topology,
the devices can once again be reached in the resulting new topology.
In the redundancy manager, the 2 ring ports are disconnected from each other if the network
is uninterrupted. This prevents circulating data frames. In terms of data transmission, the ring
topology is a linear bus topology. The redundancy manager monitors the ring topology. 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 redundancy
manager.