GE 350 Communications Manual page 38

REDUNDANCY OPTIONS
3–4
Figure 3-3: Example of PRP Redundant Network
Under normal circumstances both frames will reach their destination and one of them will
be sent up the OSI stack to the destination application, while the second one will be
discarded. If an error occurs in one of the networks and traffic is prevented from flowing on
that path, connectivity will still be provided through the other network to ensure
continuous communication. However, care must be taken when designing the two LANs,
so that no single point of failure (such as a common power supply) is encountered, as such
scenarios can bring down both LANs simultaneously.
PRP uses specialized nodes called doubly attached nodes (DANPs) for handling the
duplicated frames. DANPs devices have an additional module at the link layer level, called
the Link Redundancy Entity (LRE). LRE is responsible for duplicating frames and adding the
specific PRP trailer when sending the frames out on the LAN, as well as making decisions
on received frames as to which one is sent up the OSI stack to the application layer and
which one is discarded. In essence LRE is responsible for making PRP transparent to the
higher layers of the stack. There is a second type of specialized device used in PRP
networks, called RedBox, with the role of connecting Single Attached Nodes (SANs) to a
redundant network.
SR3 relays implement only the DANP functionality. The RedBox functionality is not
implemented.
The original standard IEC 62439-3 (2010) was amended to align PRP with the High-
availability Seamless Redundancy (HSR) protocol. To achieve this, the original PRP was
modified at the cost of losing compatibility with the PRP 2010 version. The revised
standard IEC 62439-3 (2012) is commonly referred to as PRP-1, while the original standard
is PRP-0. The SR3 relays support only PRP-1.
PRP can be enabled in configuration through a setting available on the network
configuration menu, REDUNDANCY, which already has the capability of enabling Failover
redundancy. When REDUNDANCY is set to PRP, the ports dedicated for PRP will operate in
redundant mode.
The rights associated with configuring PRP follow the security requirements for network
configuration.
PRP management through SNMP MIB is not supported, as SR3 doesn't currently support
SNMP for configuration. Settings and actual values are only available through the front
panel and through EnerVista.
The PRP solution to implemented must ensure that performance requirements stated in
IEC 61850-5 Clause 13 are still met. It is specified under Clause 13 (Message performance
requirements) that messages of type 1A must meet the performance class P2/3, which is
3ms (See 3.7.1.1).
Each device in the daisy chain forwards the message until it reaches the destination.
CHAPTER 3: ETHERNET INTERFACE
350 FEEDER PROTECTION SYSTEM – COMMUNICATIONS GUIDE