Users Guide

1008 Ethernet Ring Protection
• The incoming R-APS message requests a protection switch.
Ring Failure Detection
Protection switching on the ring node occurs when a Continuity Check
Message (CCM) fault is reported on one of the ring links or when a physical
layer failure condition is reported to the ERP control process.
The Ethernet layer connectivity of ring links is periodically monitored using
down Maintenance Entity Endpoints (MEPs). OAM reports a CCM fault
when it does not receive the expected CCM for 3.5 times the configured
CCM interval. When OAM detects the failure, it signals the ERP control
process to initiate the protection switchover.
The ring node detecting the failure will block that port for its protected
VLANs and generate an R-APS (SF) message. It will send this R-APS (SF)
message out both of its ring ports. The R-APS is first sent as a burst of three
R-APS messages and then continues to send this message every five seconds
until the Signal Fail (SF) condition recovers.
When the R-APS message is received at the RPL owner and the RPL
neighbor, this indicates that there is a block somewhere else in the ring, and
this allows the RPL owner and RPL neighbor to unblock their RPL. The RPL
owner also notes that the Node ID and BPR received in the R-APS message is
not that of itself and its RPL. At this point, the ring has completed the
protection switchover.