Siemens SIMATIC NET S7-400 Manual page 13

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).
Connecting up and cabling
Each frame duplicate sent using the PRP mechanisms is given in identifier that specifies
whether it is sent via LAN A or LAN B.
Note
Cabling
Make sure that all the PRP ports of the nodes and the SCALANCE X204RNA /
RUGGEDCOM RS950G on LAN A and LAN B are connected correctly. A frame with the
identifier "LAN A" must be received at the corresponding port.
The PRP ports of SIMATIC NET devices have the following identifiers. The CP ports are the
ports of the interface with PRP capability.
● Ports for connection to LAN A
– CPs: X2/P1
– SCALANCE X204RNA: PRP A
● Ports for connection to LAN B
– CPs: X2/P2
– SCALANCE X204RNA: PRP B
How is a redundant PRP network set up?
A network topology in which the Parallel Redundancy Protocol is used (PRP network)
consists of two separate Ethernet subnets. The structure of the two subnets does not need
to be identical.
CP 443-1 RNA
Manual, 03/2019, C79000-G8976-C299-04
Application and functions
1.3 Network topology with redundancy (PRP)
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