Edge-Core ECS4120-28F, Reference Manual, Page: 535 / 938

Chapter 20
| ERPS Commands
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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.
■
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 erps clear command 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.
◆
Recovery for Forced Switching – An erps forced-switch command is removed
by issuing the erps clear command 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 keeps the ring port
blocked for the traffic channel and for the R-APS channel, due to the previous
Forced Switch command. This ring port is kept blocked 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.
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.