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99.1 ERPS Overview
The Ethernet Ring Protection Switching (ERPS) feature, defined in ITU-T G.8032, specifies protection
switching mechanisms for Ethernet layer network rings. This feature provides protection for Ethernet
traffic from forming loops, which might fatally affect network operation. An Ethernet ring consists of
multiple Ethernet ring nodes, and the minimum number of Ethernet ring nodes is two. Each Ethernet ring
node is connected to adjacent Ethernet ring nodes with two independent links. A ring link is bound by
two adjacent Ethernet ring nodes, and a port of a ring link is called a ring port. Loop avoidance is
achieved by ensuring Ethernet traffic flows on all but one of the ring links. This particular link is called the
Ring Protection Link (RPL), which is always blocked under normal conditions.
The following is a list of RPL nodes and their functions:
• RPL Owner - The RPL owner is responsible for blocking traffic at one end of the RPL so that no loops are
formed. Each Ethernet ring can have one RPL owner only.
• RPL Neighbor - The RPL neighbor node is an optional Ethernet ring node adjacent to the RPL,
responsible for blocking or unblocking its end of the RPL.
Figure 293 ITU-T G.8032 Ethernet Ring Topology
RPL Neighbor
Chapter 99 ERPS
RPL Owner
RPL Block
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