Chapter 20
| ERPS Commands
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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.
â–
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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