1761   Wrong presentation of a HSR-PRP coupling device

Created: 26 Feb 2021

Status: Accepted

Part: Part 90-4 (2020; Edition 2, Network Engineering)


Page: 236

Clause: 19.7.5

Paragraph: Figure 102 – Coupled PRP and HSR networks


On the diagram, a HSR-PRP coupling device is shown as a single 4-port device (called "COUPLER"). Such a 4-port device is not defined in the IEC 62439-3(:2016) standard; instead, 62439-3 defines a HSR-PRP coupler as a 3-port device, where 2 ports are connected to an HSR ring and the 3-rd port is connected to one of the PRP LAN's - see IEC 62439-3:2016, chapter, Figure 16.


As shown in IEC 62439-3:2016, chapter, Figure 16, two 3-port HSR-PRP coupling devices are required to connect a PRP network to a HSR ring.
So, in Figure 102 replace one 4-port coupler with two 3-port couplers, according to IEC 62439-3:2016, chapter, Figure 16.

Discussion Created Status
I think it would be beneficial to adapt the example to meet the requirement of redundancy: using 2 red boxes.

05 Mar 21 Accepted
The observation is correct. Figure 102 has no counterpart in IEC 62439-3 since obviously the "COUPLER" is a single point of failure. A structure with two RedBoxes as IEC 62439-3 or Figure 52 & 52 show should be used in demanding applications. However, the architecture of Figure 102 is not prohibited if the application can tolerate this single point of failure (it is an actual example supplied by a company). The exemple was chosen to demonstrate how the SCD should look like in such a case, rather than as a recommendation to do so. So, a NOTE should be added that this construct presents a single point of failure and should be used in applications that tolerate such.
26 Feb 21 Accepted


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