Edge-Core ECS4660-28F, Management Manual, Page: 1316 / 2020

C
HAPTER
39
| ERPS Commands
– 1316 –
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.
■
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.
■
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.