ECS4100 Series CLI Reference Guide-R07

Chapter 24 | ERPS Commands
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Non-revertive behavior for Protection, Forced Switch, and Manual Switch states
are basically the same. Non-revertive behavior requires the erps clear
command to used to return the RPL from Protection state to Idle state.
◆ Recovery for Protection Switching – A ring node that has one or more ring ports
in an SF (Signal Fail) condition, upon detecting the SF condition cleared, keeps
at least one of its ring ports blocked for the traffic channel and for the R-APS
channel, until the RPL is blocked as a result of ring protection reversion, or until
there is another higher priority request (e.g., an SF condition) in the ring.
A ring node that has one ring port in an SF condition and detects the SF
condition cleared, continuously transmits the R-APS (NR – no request) message
with its own Node ID as the priority information over both ring ports, informing
that no request is present at this ring node and initiates a guard timer. When
another recovered ring node (or nodes) holding the link block receives this
message, it compares the Node ID information with its own Node ID. If the
received R-APS (NR) message has the higher priority, this ring node unblocks its
ring ports. Otherwise, the block remains unchanged. As a result, there is only
one link with one end blocked.
The ring nodes stop transmitting R-APS (NR) messages when they accept an R-
APS (NR, RB – RPL Blocked), or when another higher priority request is received.
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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.