Redundant Network Access – RNA

Redundant network structures increase network availability, but usually also result in short-term delays in data transfer when a connection is switched to a different network path in the event of a failure.

Message frame delay is no longer a problem thanks to Redundant Network Access (RNA) from Siemens Industry for hardware and software which support both PRP (Parallel Redundancy Protocol) and HSR (High-availability Seamless Redundancy Protocol):

PRP redundancy protocol

Via two separate networks and with the PRP method in accordance with the IEC 62439-3 standard, it is possible to design a network structure which always guarantees a transfer of one of the two frames in the event of an error in one of the two networks. In this way, the transfer of the frame is always ensured without a delay in the case of an error.

The PRP redundancy method can be used both in manufacturing and process automation applications with very high availability requirements and in substation applications for electrical energy distribution, such as in medium- and high-voltage switch gear.

Seamless redundant communication with the PRP method

HSR redundancy protocol

In ring-shaped network structures, seamless data transfer for plants requiring high availability (for example, process automation) is implemented using the HSR method (High Availability Seamless Redundancy Protocol according to IEC 62439-3). The SCALANCE X204RNA devices with HSR functionality can also be used for the single and redundant transition from HSR to PRP network structures.


The transfer of the frames without any delay is therefore always ensured even if a fault occurs – and even in environments prone to strong interference. This makes the learning of communications paths (reconfiguration time) as is required with most of the other methods unnecessary.

RNA network solutions with Parallel Redundancy Protocol provide

  • Very high plant availability as a result of parallel data transfer via separate network structures

  • No frame delays during reconfiguration of one of the two network structures

  • High flexibility in network design because network structures can be executed as line, tree, star and ring structures

  • Fast commissioning without mandatory configuration

Seamless redundant communication with the HSR method