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PACSystems* RX3i PROFINET Controller Manual
– December 2011
GFK-2571A
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PROFINET Media Redundancy Protocol
PROFINET Media Redundancy Protocol (MRP) supports devices configured in a ring topology with
a maximum of 1 Manager and 63 Clients. It is based on the functions of IEC 62439. Media
Redundancy Protocol is not routable between different IP subnets.
Each device within a Redundant Media network has at least two physical pathways to two other
devices on the network. To connect to the ring, each device requires an integrated switch with at
least two external ports (ring ports) that support Media Redundancy Protocol. Devices that are not
MRP-capable can be connected to a device like an MRP-capable switch in the ring, but they cannot
be in the ring themselves. The redundant paths only extend to the devices on the ring that are MRP-
capable and enabled.
One of the devices on the ring must be configured as the Media Redundancy Manager (MRM), and
all the other devices must be configured as Media Redundancy Clients (MRCs).
The Media Redundancy Manager disables one of the segments of the ring so that a loop is not
created in the network. To disable a segment, the Media Redundancy Manager either:
blocks one of its two Ethernet switch ports used to form the ring when the ring is closed, or
forwards both switch ports if one of the other ring segments is missing (ring open) and passes
messages through the Media Redundancy Manager to get to devices on the other side of the
failed segment.
The RX3i PROFINET Controller can be used as either a Media Redundancy Manager or Client. The
VersaMax PNS can be used as a Media Redundancy Client.
MRP Failover Performance
A network using Media Redundancy Protocol recovers from a ring failure within 200 milliseconds
when running at 100 Mbps full duplex with default values. Actual failover time depends on the
device responsiveness to network disconnection and reconnection, number of devices in the ring,
media speed, length of media, and frequency of sending test frames over the network. Network
recovery time is shorter with fewer devices, faster media speed, and shorter media lengths. If all
devices provide LinkUp/LinkDown indications, the network recovery time will be significantly shorter
than 200ms. Third-party devices in the MRP ring may introduce additional network recovery time.
When MRCs do not provide LinkUp/LinkDown detection, network recovery time also depends upon
the
test packet timeout interval
, which is the product of the Default Test Interval and the Test
Monitoring Count plus 1 that have been set for the Media Redundancy Manager. These parameters
determine the frequency for network integrity checks and the number of failed integrity checks to
allow before declaring a ring failure. For an RX3i PNC module acting as Media Redundancy
Manager, these parameters are set as part of the Proficy Machine Edition hardware configuration.
(For example, the default test packet timeout interval is 20ms × (3+1) = 80ms.)
Each device in the ring must be able to detect the failure or recovery of a connection. When using
third-party devices in a redundant media ring, failover time will be affected by the performance of
these devices. For devices that do not detect the failure or recovery of a connection via
LinkUp/LinkDown indication, the shortest guaranteed failover time will be the
test packet timeout
interval,
as described above.
