Profinet Media Redundancy Protocol; Mrp Failover Performance - Emerson PACSystems RX3i User Manual

RSTI-EP PROFINET I/O Controller User Manual
GFK-2571R
6.1

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 may not be routed 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 extend only 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 PROFINET Controller can be used as either a Media Redundancy Manager or Client. The
PNS can be used as a Media Redundancy Client.
Typically, one PROFINET Controller module in each ring I/O network is configured as the
media redundancy manager. All other nodes in the ring (I/O Devices, network switches, and
other PROFINET Controllers) must be configured as media redundancy clients.
6.1.1

MRP Failover Performance

A network using Media Redundancy Protocol recovers from a ring failure within 80
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 MRC devices provide LinkUp/LinkDown indications, the
network recovery time will be significantly shorter than 80ms. 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 PACSystems
PROFINET Controller acting as Media Redundancy Manager, these parameters are set as
Redundant Media
Section 6
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