Figure 73. Normal Operation (No-Fault) - Alcatel-Lucent 9500 MPR User Manual

2.8.10.1.6 ERPS Instance
An ERPS Instance is an entity responsible for the protection of a subset of the VLANs that transport traffic
over the physical ERPS Topology. Each ERPS Instance is independent of other ERPS Instances that may
be configured on the physical ERPS Topology. Only two ERPS instances are supported.
Each ERPS Instance has its own RPL and RPL Owner.
Additionally, an independent session of R-APS protocol is used, over a dedicated R-APS VID, for the
ERPS Instance protection coordination.
2.8.10.2 ERPS operation
The protection switching mechanism is based on the Automatic Protection Switching protocol for Ethernet
ring topologies (called R-APS). This protocol is used to coordinate the protection actions over the ring.
The fundamentals of this ring protection switching architecture are:
– principle of loop avoidance.
– utilization of learning, forwarding, and address table mechanisms defined in the Ethernet flow for-
warding function.
The loop avoidance in the ring is achieved by guaranteeing that, at any time, traffic may flow on all but
one of the ring links. This particular link is called the Ring Protection Link (RPL).
Under normal conditions this link is blocked, i.e., not used for traffic. One designated node, the RPL
Owner, is responsible to block traffic over the RPL.
Under a ring failure condition, the RPL owner is responsible to unblock the RPL, allowing the RPL to be
used for traffic.
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Figure 73. Normal Operation (No-fault)

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