Chapter 6. Redundant Media
GFK-2571N
May 2018
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6.1.3
MRP Operation for I/O Update Rates of 16ms or Greater
The PACSystems RX3i PROFINET IO Controller supports bumpless operation at 16ms with the
requirement that the MRP Manager be configured for an MRP Test Packet Interval and MRP Test
Packet Count that is faster than the fastest IO timeout possible.
For example:
Assume the worst-case scenario when a ring break occurs immediately after the device received a
test packet and immediately before the device was scheduled to receive an I/O packet. In the case of
a 16ms I/O Update Rate, a timeout will occur after three consecutive missed I/O packets, which can
occur in slightly over 32ms. Assuming that the Test Packet Interval is configured for 10ms and the
Test Packet Count is configured for 2, the PROFINET Controller can detect a ring break in just less
than 30ms. This ring recover scenario would look like the following timeline.
Figure 98: Timeline for Successful MRP Ring Repair at 16ms I/O Update Rate
To ensure a successful ring recovery using the Test Packets at a 16ms I/O Update rate or above,
make sure the following statement is true:
Test Packet Interval × (Test Packet Count + 1) < I/O Update Rate × 2
6.1.4
MRP Operation at I/O Update Rates Less Than 16ms
The PACSystems implementation of MRP supports fast LinkUp/LinkDown detection on devices, an
optional part of the MRP standard. This allows an MRC experiencing a network link failure or recovery
to send LinkUp/LinkDown messages to the MRM immediately. The MRM can heal the network
without needing to wait for multiple test-packet timeouts to detect the failure. This feature allows
the network recovery time to be significantly shorter than the test packet timeout interval because
the break is detected immediately.
6.1.5
Minimum I/O Rate When Configured in an MRP Ring
The minimum I/O rate that is possible for bumpless operation depends on the speed and the type of
physical connection being used for the MRP ring ports. PACSystems PROFINET I/O Controllers
support a specified number of PACSystems PROFINET I/O devices running at or above the minimum
I/O Update Rate listed in the table below.
