RSTI-EP PROFINET I/O Controller User Manual
Section 6
GFK-2571R
May 2021
Redundant Media
134
For bumpless network recovery (without disturbing IO communications to an I/O-Device),
the I/O Update Rate for the I/O-Device should be configured to be greater than 1/2 of the
network recovery time. This permits the ring to be disconnected or reconnected without
timing out the communication connection between the I/O Device and its I/O-Controller.
In order to insure correct MRP operation, it is important to connect the correct Ethernet
ports of the PROFINET Controller and devices to the MRP ring. The ports connected to the
ring must be the same ports configured as MRP Ring Ports. Failure to connect the configured
ports will prevent the PROFINET Controller and devices from correctly participating in the
MRP ring.
Disclaimer: Pulling a fiber SFP cable out of the SFP cage (as opposed to cutting a fiber cable),
can have unpredictable performance (and may lose devices in a properly configured MRP
ring) due to the fact that the light is still seen by the SFP as the cable is being removed so
that data is lost significantly before the SFP can detect that the connection has been lost.
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. If 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:
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