Edge-Core ECS4120-28F, Reference Manual, Page: 547 / 938

Chapter 20
| ERPS Commands
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While an existing forced switch request is present in a ring, any new forced
switch request is accepted, except on a ring node having a prior local forced
switch request. The ring 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 Command Usage section for the
non-revertive command.
◆
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
Table 101: 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