ECS4110-52T_Management Guide

C HAPTER 14 | Basic Administration Protocols
Ethernet Ring Protection Switching
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Recovery with Revertive Mode – When all ring links and ring
nodes have recovered and no external requests are active,
reversion is handled in the following way:
a. The reception of an R-APS (NR) message causes the RPL
Owner Node to start the WTR (Wait-to-Restore) timer.
b. The WTR timer is cancelled if during the WTR period a higher
priority request than NR is accepted by the RPL Owner Node
or is declared locally at the RPL Owner Node.
c. When the WTR timer expires, without the presence of any
other higher priority request, the RPL Owner Node initiates
reversion by blocking its traffic channel over the RPL,
transmitting an R-APS (NR, RB) message over both ring
ports, informing the ring that the RPL is blocked, and
performing a flush FDB action.
d. The acceptance of the R-APS (NR, RB) message causes all
ring nodes to unblock any blocked non-RPL link that does not
have an SF condition. If it is an R-APS (NR, RB) message
without a DNF (do not flush) indication, all ring nodes flush
the FDB.
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Recovery with Non-revertive Mode – In non-revertive operation,
the ring does not automatically revert when all ring links and
ring nodes have recovered and no external requests are active.
Non-revertive operation is handled in the following way:
a. The RPL Owner Node does not generate a response on
reception of an R-APS (NR) messages.
b. When other healthy ring nodes receive the NR (Node ID)
message, no action is taken in response to the message.
c. When the operator issues the Clear command (Configure
Operation page) for non-revertive mode at the RPL Owner
Node, the non-revertive operation is cleared, the RPL Owner
Node blocks its RPL port, and transmits an R-APS (NR, RB)
message in both directions, repeatedly.
d. Upon receiving an R-APS (NR, RB) message, any blocking
node should unblock its non-failed ring port. If it is an R-APS
(NR, RB) message without a DNF indication, all ring nodes
flush the FDB.
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Recovery for Forced Switching – A Forced Switch command is
removed by issuing the Clear command (Configure Operation
page) to the same ring node where Forced Switch mode is in
effect. The clear command removes any existing local operator
commands, and triggers reversion if the ring is in revertive
behavior mode.
The ring node where the Forced Switch was cleared continuously
transmits the R-APS (NR) message on both ring ports, informing
other nodes that no request is present at this ring node. The
ring nodes stop transmitting R-APS (NR) messages when they