Edge-Core ECS4660-28F, Management Manual, Page: 546 / 2020

C
HAPTER
14
| Basic Administration Protocols
Ethernet Ring Protection Switching
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under maintenance in order to avoid falling into the above
mentioned unrecoverable situation.
■
Manual Switch – Blocks specified ring port, in the absence of a
failure or an FS command.
■
A ring with no request has a logical topology with the traffic
channel blocked at the RPL and unblocked on all other ring links.
In this situation, the Manual Switch command triggers
protection switching as follows:
a.
If no other higher priority commands exist, the ring node,
where a manual switch command was issued, blocks the
traffic channel and R-APS channel on the ring port to which
the command was issued, and unblocks the other ring port.
b.
If no other higher priority commands exist, the ring node
where the manual switch command was issued transmits R-
APS messages over both ring ports indicating MS. R-APS
(MS) message are continuously transmitted by this ring node
while the local MS command is the ring node’s highest
priority command (see Table 35 on page 545 ). The R-APS
(MS) message informs other ring nodes of the MS command
and that the traffic channel is blocked on one ring port.
c.
If no other higher priority commands exist and assuming the
ring node was in Idle state before the manual switch
command was issued, the ring node flushes its local FDB.
d.
A ring node accepting an R-APS (MS) message, without any
local higher priority requests unblocks any blocked ring port
which does not have an SF condition. This action
subsequently unblocks the traffic channel over the RPL.
e.
A ring node accepting an R-APS (MS) message, without any
local higher priority requests stops transmitting R-APS
messages.
f.
A ring node receiving an R-APS (MS) message flushes its
FDB.
■
Protection switching on a manual switch request is completed
when the above actions are performed by each ring node. At
this point, traffic flows around the ring are resumed. From this
point on, the following rules apply regarding processing of
further manual switch commands:
a.
While an existing manual switch request is present in the
ring, any new manual switch request is rejected. The request
is rejected at the ring node where the new request is issued
and a notification is generated to inform the operator that
the new MS request was not accepted.
b.
A ring node with a local manual switch command which
receives an R-APS (MS) message with a different Node ID
clears its manual switch request and starts transmitting R-
APS (NR) messages. The ring node keeps the ring port
blocked due to the previous manual switch command.