Siemens SIMATIC NET S7-400 Manual page 12

Application and functions
1.3 Network topology with redundancy (PRP)
Some devices of the SCALANCE X-200RNA product line also support the redundancy
protocol "High-availability Seamless Redundancy" (HSR).
Parallel Redundancy Protocol (PRP)
The Parallel Redundancy Protocol (PRP) is a redundancy protocol for Ethernet networks. It
is specified in IEC 62439-3.
The areas of application of PRP are distributed applications with high reliability demands that
depend on the high availability of the network. Compared with classic fault-tolerant networks,
bumpless path redundancy is possible with PRP.
PRP has the advantage that it uses parallel, separate networks made up of standard
network components. End devices that use this method are connected to both networks via
two ports of an interface of the device or via a SCALANCE X-200RNA or a RUGGEDCOM
RS950G. This means that data of the end device can be transferred at the same time via
both networks. If a transmission path is interrupted, the data reaches the communications
partner via the second parallel path.
If a network is interrupted, communication can be maintained with PRP via the second
network without any interruption. Reconfiguration times required with the other redundancy
protocols (e.g. MRP) do not therefore apply.
An end device with PRP capability can be connected to redundant networks by using the
PRP protocol. An end device that does not have PRP capability can be connected to a
redundant network via a SCALANCE X-200RNA or RUGGEDCOM RS950G that does have
PRP capability. This means that PRP can also be used by end devices without PRP
capability.
Devices with PRP capability are located in two independent networks with the same MAC
and IP address.
Communication with PRP
PRP is only possible when two end devices are connected via two independent networks
(LAN A and LAN B).
Each end device is represented in both networks LAN A and LAN B with the same MAC and
IP address.
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CP 443-1 RNA
Manual, 03/2019, C79000-G8976-C299-04