363-206-305
Maintenance Description
9-16
Issue 3 June 2000
Figure 9-6. Path Protection Switching
The user can set STS-1 and VT1.5 signal degrade thresholds using the
set-sts1
,
set-vt1
,
rtrv-sts1
, and
rtrv-vt1
commands at a
drop
node on
a protected ring. Under normal conditions, both incoming SONET path signals to
the switch selection point are of high quality, and the signal can be selected from
either ring. A failure or a transmission degradation on one of the rings requires
that the other ring path be selected; path selection occurs within 60 milliseconds
after a hard failure condition. Figure 9-6b shows how traffic is switched when a
dual-fiber cut occurs. The system provides nonrevertive switching to minimize the
impact on critical customer services by giving the service provider control when,
and if, the critical service should revert to a particular ring. A manual path
protection switching command allows switching back to the original path for ease
of ring maintenance. Refer to the
switch-path-vt1
or
switch-path-sts1
command in Chapter 11, "Commands and Reports.”
Node C
Node A
Node BNode D
AC
CA
(a.) Normal Operation
Node A
Node BNode D
AC
CA
AC
CA
Node C
AC
CA
(b.) Path Failure
SWITCH
MADE
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