C
HAPTER
34
| ERPS Commands
– 1098 –
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Recovery with non-revertive mode is handled in the following way:
a. The RPL Owner Node, upon reception of an R-APS(NR) message
and in the absence of any other higher priority request does not
perform any action.
b. Then, after the operator issues the erps clear command at the
RPL Owner Node, this ring node blocks the ring port attached to
the RPL, transmits an R-APS (NR, RB) message on both ring
ports, informing the ring that the RPL is blocked, and flushes its
FDB.
c. The acceptance of the R-APS (NR, RB) message triggers all ring
nodes to unblock any blocked non-RPL which does not have an
SF condition. If it is an R-APS (NR, RB) message without a DNF
indication, all ring nodes flush their FDB. This action unblocks
the ring port which was blocked as result of an operator
command.
◆ Recovery for Manual Switching – An erps manual-switch command is
removed by issuing the erps clear command at the same ring node
where the Manual Switch 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 Manual Switch was cleared keeps the ring port
blocked for the traffic channel and for the R-APS channel, due to the
previous Manual 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 Ethernet Ring Node where the Manual Switch was cleared
continuously transmits the R-APS (NR) message on both ring ports,
informing 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 Manual 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 on both ring ports.
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Recovery with revertive mode is handled in the following way:
a. The RPL Owner Node, upon reception of an R-APS (NR) message
and in the absence of any other higher priority request, starts
the WTB timer and waits for it to expire. While the WTB timer is
running, any latent R-APS (MS) message is ignored due to the
higher priority of the WTB running signal.
b. When the WTB timer expires, it generates the WTB expire
signal. The RPL Owner Node, upon reception of this signal,
initiates reversion by blocking the traffic channel on the RPL,
transmitting an R-APS (NR, RB) message over both ring ports,
informing the ring that the RPL is blocked, and flushes its FDB.
c. The acceptance of the R-APS (NR, RB) message causes all ring
nodes to unblock any blocked non-RPL that does not have an SF
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