Web Management Guide-R05

Chapter 13 | Basic Administration Protocols
Ethernet Ring Protection Switching
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c. A ring node accepting an R-APS (FS) message, without any local
higher priority requests unblocks any blocked ring port. This action
subsequently unblocks the traffic channel over the RPL.
d. The ring node accepting an R-APS (FS) message, without any local
higher priority requests stops transmission of R-APS messages.
e. The ring node receiving an R-APS (FS) message flushes its FDB.
■
Protection switching on a forced 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 forced switch commands:
■
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.
Table 31: ERPS Request/State Priority
Request / State and Status Type Priority
Clear local highest
FS local |
R-APS (FS) remote |
local SF
*
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 |