Chapter 13
| Basic Administration Protocols
Ethernet Ring Protection Switching
– 485 –
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.
â–
Recovery for forced switching under revertive and non-revertive
mode is described under the Revertive parameter.
â–
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.
Table 30: 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
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