Appendix D: About Redundancy
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D
About Redundancy
Redundancy role on the network is to help protect critical links against failure, protects against
network loops, and keeps network downtime at a minimum. Sustainable, uninterrupted data
communication network is critical for industrial applications.
Network Redundancy allows user to set up redundant loops in the network to provide a backup
data transmission route in the event that a cable is inadvertently disconnected or damaged.
The switch supports Rapid Spanning Tree Protocol (RSTP)/Multiple Spanning Tree Protocol
(MSTP) and ITU-T G.8032 v1/v2 Ethernet Ring Protection Switching (ERPS). ERPS (Ethernet Ring
Protection Switching) or ITU-T G.8032 is a loop resolution protocol, just like STP.
Convergence time is much quicker in ERPS. Unlike in STP, most of the ERPS parameters are
management configured – which link to block in the start etc.
Normally ERPS is implemented with-in the same administrator domain, there by having control
on the nodes participating in the Ring.
This technology provides sub-50 ms protection and recovery switching for Ethernet traffic. This is
a particularly important feature for industrial applications, since it could take several minutes to
locate the disconnected or severed cable.
D.1
Spanning Tree Protocol (STP)
STP is a Layer 2 link management protocol that provides path redundancy while preventing loops
in the network.
For a Layer 2 Ethernet network to function properly, only one active path can exist between any
two stations.
Spanning-tree operation is transparent to end stations, which cannot detect whether they are
connected to a single LAN segment or a switched LAN of multiple segments.
D.2
Rapid Spanning Tree Protocol (RSTP)
If the destination from a switch is more than one path, it will lead to looping condition that can
generate broadcast storms in a network.
The spanning tree was created to combat the negative effects of message loops in switched
networks.
A spanning tree algorithm is used to automatically sense whether a switch has more than one
way to communicate with a node. It will then select the best path, and block the other path.
Spanning Tree Protocol (STP) introduced a standard method to accomplish this.
Rapid Spanning Tree Protocol (RSTP) was adopted and represents the evolution of STP, providing
much faster spanning tree convergence after a topology change.
D.3
Multiple Spanning Tree Protocol (MSTP)
MSTP is a direct extension of RSTP that can provide an independent spanning tree for different
VLANs.
It simplifies network management by limiting the size of each region, and prevents VLAN
members from being segmented from the group.
Anybus
®
Managed Industrial L3 Switch User Manual
SCM-1202-151 1.1 en-US
