Web Management Guide-R04

Table Of Contents
Chapter 13
| Basic Administration Protocols
Ethernet Ring Protection Switching
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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 nodes 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.
Table 34: 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