56 Rockwell Automation Publication ICSTT-RM447M-EN-P - July 2019
Chapter 3 Controller Functionality
faults occur and managing the communications redundancy. An SNCP
network is illustrated in the diagram.
First there must be a physical connection between the two controllers. The
design of the Ethernet network and the equipment used does not impact the
SIL rating of the communications interface, but the design of the network does
change the reliability of the network and does impact the spurious trip rate.
SNCP Network data can be combined on a common network resulting in
safety and non-safety data sharing a common physical network. This does not
compromise the SIL rating of the network but again does introduce failure
modes and possibly security risks which can increase the spurious trip rate.
Therefore, careful consideration must be given to the network topology during
the applications specification and design phase.
SNCP Networks can be configured as Simplex (Fail Safe) or Redundant (Fault
tolerant). The network configuration is dependent on the applications safety
and availability requirements. The giving and receiving of data occurs
independently from the physical network configuration as the connection
between the controllers is treated as a logical network
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