When establishing communication between industrial servers and networks, two types of protocols can be used, which are the ones we'll be discussing today: PRP and HSR redundant industrial communication protocols.

¿Cómo son PRP y HSR?

We'll explain how they work and what their features are the two most important redundant industrial communication protocols en la Industrial communication.

Protocolo PRP

PRP It ensures high availability and reduces the time it takes for the network to recover, thereby also reducing transmission time to zero.

It is based on the use of two networks, LAN A and LAN B, which are independent at all levels and receive the same message at the same time.

A frame with the same MAC and IP addresses will be sent over both interfaces but on different ports.

Protocolos de comunicación industrial

Whether or not this protocol is used, the configuration of the industrial networks and the routers do not need to be changed. Latency will remain similar in both, though not exactly the same, given that there will be a time difference in the second frame.

This protocol is encapsulated in an IP network frame, allowing for transparent use of the protocol, so that both PRP devices and non-PRP devices can communicate over it.

Thus, we may encounter two types of devices for each network: one with built-in redundancy (DANP) and another without it (SAN).

DANP Devices

These devices from the protocolo PRP They implement an additional operation specific to this layer, which is carried out through an LRE that is responsible for duplicating frames and managing redundant frames while remaining transparent to the other OSI layers at Layer 2. The LRE:

  • Receives a Layer 3 link-trace.
  • Respond by creating two new frames and adding RCT bytes after the IP header.
  • Send the frames over the port corresponding to the two independent networks.
  • At the receiver, the RCT is removed, and the frame is also forwarded to the upper layers.
  • Frame discarding is typically performed to remove duplicate frames from the LRE.

Protocolo HSR

HSR is a redundant protocol, like PRP. This ensures high availability while reducing both network recovery time and transmission time to zero.

In this case, it is based on device redundancy, converting a Layer 3 frame into two identical HSRs that are sent through the device's two ports to a ring-topology network but in opposite directions. Devices connected to this network are called DANHs.

Although it also operates on Layer 2, the protocolo HSR It will modify the Ethernet frame headers by adding the new fields; this is why there must be only DANH nodes.

Protocolo de comunicación industrial HSR

The most notable differences compared to the PRP protocol are:

  • There is only one LAN with a ring topology.
  • Any device will understand the protocol; they are DANH nodes.
  • The switches, which are SAN switches, are not inserted into the ring.
  • The devices send and receive frames, with an additional feature that acts as a bridge.

Note that SAN devices can be converted to VAND, supporting both HSR and PRP protocols, as follows:

  • Regardless of the device they are mirrored to.
  • Reusable, with the ability to switch devices, protocols, or networks as needed.

In addition, depending on its configuration:

  • They will allow us to choose the output protocol.
  • At the same time, they duplicate the code for different devices.
  • They can be reconfigured remotely, allowing redundant devices to be removed without downtime or manual rewiring.
  • Security is also configurable.