Operating hardware
4.4 Media redundancy
CP 1604 / CP 1616
Operating Instructions, 02/2017, C70000-G8976-C218-08
77
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
Before physically closing the ring, download the configuration of your STEP 7 project to the
individual devices.
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.
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.
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:
●
HSR (High Speed Redundancy)
Reconfiguration time: 0.3 seconds
●
MRP (Media Redundancy Protocol)
Reconfiguration time: 0.2 seconds
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 want to introduce media redundancy in a ring topology in your STEP 7 project, select
the "MRP" function.
