Web Management Guide-R05

Chapter 13 | Basic Administration Protocols
Ethernet Ring Protection Switching
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Recovery for forced switching under revertive and non-
revertive mode is described under the Revertive parameter.
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When a ring is under an FS condition, and the node at which
an FS command was issued is removed or fails, the ring
remains in FS state because the FS command can only be
cleared at node where the FS command was issued. This
results in an unrecoverable FS condition.
When performing a maintenance procedure (e.g., replacing,
upgrading) on a ring node (or a ring link), it is recommended
that FS commands be issued at the two adjacent ring nodes
instead of directly issuing a FS command at the ring node under
maintenance in order to avoid falling into the above mentioned
unrecoverable situation.
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Manual Switch – Blocks specified ring port, in the absence of a failure or an
FS command. (Options: West or East)
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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 31 on page 467). 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
R-APS (NR, RB) remote |
R-APS (NR) remote lowest
* If an Ethernet Ring Node is in the Forced Switch state, local SF is ignored.
Table 31: ERPS Request/State Priority (Continued)
Request / State and Status Type Priority