SPRT769 December   2023 AM2431 , AM2432 , AM2434 , AM6421 , AM6422 , AM6441 , AM6442

 

  1.   1
  2.   Abstract
  3. 1 Introduction
  4. 2 Industrial Communications Terminology
  5. 3 Industrial Communication Feature Support
  6. 4 Industrial Communications Device Support
  7. 5 Industrial Communications Controller Support
  8. 6 PRP Support
  9. 7 HSR Support
  10. 8 TSN Support
  11. 9 Summary
  12. 10Additional Resources

6 PRP Support

Rapid Spanning Tree Protocol (RSTP) and Media Redundancy Protocol (MRP) are two common protocols used in Ethernet networks supporting high-availability applications. Recovery time from a fault with RSTP is measured in seconds while recovery time with MRP is measured in milliseconds. For most networks, these recovery times are more than adequate. But for mission critical networks that require zero recovery time and zero downtime, protocols such as PRP and HSR are often used.

PRP is an IEC standard (IEC 62439-3 clause 4) that protects Ethernet networks against single point failures, providing high-availability operation with zero downtime. PRP networks can remain operational in the event of a node or link failure as well as during equipment maintenance or replacement cycles.

PRP provides high-availability service by using two independent networks. A PRP node has two Ethernet ports with identical MAC addresses and is referred to as a dual attached node (DAN). Each Ethernet port is connected to one of two independent networks. When a node needs to communicate with another node, the node sends duplicate frames via the two networks to the destination node. Upon receipt, the destination node passes the 1st frame to the application layer and drops the 2nd frame.

Single-port Ethernet equipment can be connected to the PRP network through the use of a redundancy box (RedBox) which connects to both networks. Single-port nodes are referred to as single-access nodes (SAN).

One of the disadvantages of a PRP network is the need for two independent networks and the resulting high cost. The total cost of a PRP network is somewhat offset by the use of standard off-the-shelf 802.1-compliant networking equipment.

PRP is referenced in the IEC 61850 standard for use in electrical substations.

The AM243x SDK includes support for 100Mbps PRP and the AM64x SDK includes support for 1Gbps PRP. See Table 9-1 and Table 9-2 for details.

Figure 7-5 illustrates the source node sending duplicate frames simultaneously to two independent networks. If there is a failure point in one of the two networks, there is still a path for one of the frames to arrive at the destination node.

Figure 6-2 shows a SAN connecting to the PRP network via a RedBox.

GUID-20231110-SS0I-ZPVH-5KWD-HZVXJGTMDLG8-low.svgFigure 6-1 PRP Network Example
GUID-20231110-SS0I-X80Z-H3GL-7CK44MB0S5RN-low.svgFigure 6-2 SAN Connection to a PRP Network