Edge-Core ECS4660-28F, Management Manual, Page: 545 / 2020

C
HAPTER
14
| Basic Administration Protocols
Ethernet Ring Protection Switching
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nodes where further forced switch commands are issued
block the traffic channel and R-APS channel on the ring port
at which the forced switch was issued. The ring node where
the forced switch command was issued transmits an R-APS
message over both ring ports indicating FS. R-APS (FS)
messages are continuously transmitted by this ring node
while the local FS command is the ring node’s highest
priority command. As such, two or more forced switches are
allowed in the ring, which may inadvertently cause the
segmentation of an ring. It is the responsibility of the
operator to prevent this effect if it is undesirable.
Ring protection requests, commands and R-APS signals have
the priorities as specified in the following table.
■
Recovery for forced switching under revertive and non-
revertive mode is described under the Revertive parameter.
■
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
Table 35: ERPS Request/State Priority
Request / State and Status Type Priority
Clear local highest
FS local |
R-APS (FS) remote |
local SF *
* If an Ethernet Ring Node is in the Forced Switch state, local SF is
ignored.
local |
local clear SF local |
R-APS (SF) remote |
R-APS (MS) remote |
MS local |
WTR Expires local |
WTR Running local |
WTB Expires local |
WTB Running local |
R-APS (NR, RB) remote |
R-APS (NR) remote lowest