HSR-PRP Design

The HSR- PRP line card extends the Raptor platform to incorporate three port redundant switches/interfaces (RedBoxes or Red for short) which can be configured in different HSR/PRP modes.

Figure 1. HSR-PRP Line Card Model

Port-I is connected to the main switch (a.k.a. Gigabit / Extreme Ethernet ports). Port-A and Port-B are the redundant switch ports to connect to other redundant ports. Each redundant switch is represented by a logical interface (a.k.a redundant interface or RED1 or RED2) that is used for configuration and statistics.

The HSR- PRP implementation adds zero failover time hardware redundancy. To achieve that, the following is implemented:

A packet is sent to the network over the Port-I. The redundant switch makes two copies and send them over the Port-A and Port-B.
The redundant switch will only forward the first copy of a packet that it receives on Port-A or Port-B to the Port-I and discards the second copy of the packet.

HSR

For HSR (IEC 62439-3 Clause 5), packets are transmitted with an HSR header and circulate in both direction through the ring topology. Unicast packets are forwarded until they reach the destination device, while multicast packets are forwarded until they reach the originator.

HSR rings allow for lower deployment costs as they are only connected to each other. Non-HSR equipment cannot be connected directly to the HSR ring but can be connected through an HSR RedBox.

Figure 2. HSR Topology

PRP

For PRP, (IEC 62439-3 Clause 4), packets are transmitted with a PRP trailer (an identifier added to the frame) in parallel to LAN A and LAN B, forming a double star topology. This is suitable for large scale networks. As the LANs use standard Ethernet equipment, even non PRP-capable devices (e.g singly attached nodes (SAN)s) can be connected to one of the LANs as it will ignore the PRP trailer.

Figure 3. PRP Topology