Siemens SIMATIC NET System Manual page 90

Network structures and network configuration
2.3 Media redundancy
two ports of an interface of the device or via a SCALANCE X-200RNA. 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 with PRP can be maintained 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 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.
PRP communication is handled using the following mechanisms:
● Send
An end device with PRP capability duplicates each frame to be sent on the PRP
interface. The two duplicates are sent via the 2 ports of the PRP interface via the two
separate networks LAN A and LAN B to the communications partner.
If the end device does not have PRP capability, the frame to be sent is duplicated by an
X-200RNA to which the end device is connected and sent via LAN A and LAN B to the
communications partner.
● Received
The two duplicates are received by an end device with PRP capability via LAN A and
LAN B on the two ports of the PRP interface.
If the end device does not have PRP capability, the receiving end device must be
preceded by an X-200RNA. The X-200RNA forwards the first frame to arrive to the
addressee. The second frame is discarded ((N-1) redundancy).
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System Manual, 09/2019, C79000-G8976-C242-10
Industrial Ethernet