ECS4110-28T_Management Guide

C HAPTER 36 | ERPS Commands
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◆ 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.
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Recovery with revertive mode is handled in the following way:
a. The reception of an R-APS (NR) message causes the RPL Owner
Node to start the WTB timer.
b. The WTB timer is cancelled if during the WTB 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 WTB timer expires, in the absence of any other higher
priority request, the RPL Owner Node initiates reversion by
blocking the 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 flushes the FDB.
d. 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
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 a result of an operator
command.
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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