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3 media redundancy in ring topologies – Siemens Industrial Ethernet Switches SCALANCE X-200 User Manual

Page 23

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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.