Fault Tolerance And Redundancy - Siemens SIMATIC NET System Manual

Basics of communication with Industrial Ethernet
1.3 Technologies of Industrial Ethernet
1.3.6

Fault tolerance and redundancy

Overview
Fault-tolerant systems are designed to reduce production downtime. Availability can be
enhanced, for example, by means of component redundancy. Communication systems are
thus extended to automation systems.
Redundant systems in Industrial Ethernet are characterized by the multiple (redundant)
presence of important automation components. When a redundant component fails,
processing of the program is not interrupted.
Redundancy is achieved by duplicating the part components such as CPU, network, CP, etc.
Monitoring and synchronization mechanisms ensure that if the active redundant connection
path fails, the previously passive (redundant) connection path takes over the communication
automatically. The connection itself remains established.
Redundant network
The following graphic illustrates the principle of the high availability based on the example of
a redundant network. The entire cable topology exists twice, in the following graphic
represented as "LAN A" and "LAN B". The connected components must be suitable for
redundant operation which is the case with the SIMATIC NET modules with "RNA" in the
name (abbreviation for "Redundant Network Access). Every component is connected to both
networks and all data is transported at the same time via both networks. If one of the
transmission paths is interrupted, communication via the parallel network remains
unaffected.
Figure 1-2
44
Topology example of a redundant network
System Manual, 09/2019, C79000-G8976-C242-10
Industrial Ethernet