Web Management Guide-R04

Chapter 13 | Basic Administration Protocols
Ethernet Ring Protection Switching
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b. The WTR timer is canceled 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 accept an RAPS (NR, RB)
message, or when another higher priority request is received.
If the ring node where the Forced Switch was cleared receives an R-APS
(NR) message with a Node ID higher than its own Node ID, it unblocks
any ring port which does not have an SF condition and stops
transmitting R-APS (NR) message over both ring ports.